Unlocking the Secrets of Aluminium Alloys: Global Designations, Properties, and Applications Explained

Section 1: Introduction to Aluminum Alloy Designations and Classifications

Aluminum and its alloys are pivotal engineering materials, prized for their favorable strength-to-weight ratios, corrosion resistance, and recyclability. The vast array of available aluminum alloys, each tailored for specific performance characteristics and manufacturing processes, necessitates a systematic approach to their identification and classification.

1.1. Importance of Standardized Designations

Standardized naming conventions are indispensable in materials science and engineering. They ensure unambiguous communication between designers, manufacturers, suppliers, and end-users, which is critical for accurate material procurement, consistent manufacturing, and reliable application performance. The historical development of multiple national and international standards, however, has led to a complex landscape of alloy designations.¹ For instance, an engineer in North America might specify an alloy using an Aluminum Association (AA) designation, while a European counterpart might use a European Norm (EN) for an equivalent or similar material. This multiplicity necessitates a thorough understanding of the major designation systems and the ability to cross-reference them to identify alloys with comparable properties and compositions. The evolution of standards, such as the European Norm unifying previous national standards like British Standards (BS), German DIN, and French NF, indicates a move towards harmonization, yet many legacy and regional systems remain prevalent and influential.¹

1.2. Overview of Major International Designation Systems

Several key organizations and standards bodies govern the designation of aluminum alloys globally:

• ANSI/AA (The Aluminum Association): This is arguably the most widely adopted system worldwide, particularly influential in North America. Wrought aluminum alloys are designated by a four-digit number, where the first digit signifies the principal alloying element or group. For example, 6xxx indicates alloys where magnesium and silicon are the primary alloying elements. Cast aluminum alloys use a similar system, often with three digits and a decimal point (e.g., 356.0). The prefix ‘AA’ often precedes the numerical designation (e.g., AA6061).¹ The second digit in wrought alloy designations, if not zero, indicates a modification of the original alloy, while the last two digits identify the specific alloy within the series (except for the 1xxx series).²
• UNS (Unified Numbering System): Predominantly used in North America, the UNS provides a unified identification for metals and alloys. For aluminum, the designation consists of the prefix ‘A’ followed by five digits. These digits are often based on existing AA numbers; for instance, AA6061 corresponds to UNS A96061, and AA7075 is UNS A97075.¹
• EN (European Norm): Developed by the European Committee for Standardization (CEN), EN standards aim to unify the various national standards of EU member states. For aluminum alloys, the prefix ‘EN’ is followed by ‘AC-‘ for cast alloys (e.g., EN AC-46100) or ‘AW-‘ for wrought alloys (e.g., EN AW-6061). This is then followed by a four-digit code that often bears resemblance to AA designations.¹
• ISO (International Organization for Standardization): The ISO system uses the chemical symbol ‘Al’ as a prefix, followed by the chemical symbols and nominal percentages of the principal alloying elements. For example, AA6061 is designated as ISO AlMg1SiCu, and AA2024 as ISO AlCu4Mg1.¹ While highly descriptive of the composition, this system is more frequently encountered in academic and research contexts than in industrial specifications.¹
• BS (British Standard): British Standards for aluminum alloys often employ alphanumeric characters. The LM series (e.g., LM4, LM6, LM25) refers to BS 1490, a standard for aluminum casting alloys.⁵ The letters in other BS designations can indicate main alloying elements, with figures representing weight percentages.⁴
• JIS (Japanese Industrial Standard): Administered by the Japanese Industrial Standards Committee, JIS designations for aluminum alloys are similar in structure to the AA system. They typically begin with the prefix ‘JIS A’, followed by four digits that represent the material’s composition.⁴ The ADC series (e.g., ADC12) is a well-known JIS classification for aluminum die-casting alloys.⁷

Other national standards, such as DIN (Germany), AFNOR (France), CSA (Canada), and SIS (Sweden), also contribute to the diversity of alloy nomenclature found in technical literature and commerce.⁴

1.3. Fundamental Alloy Categorization

Aluminum alloys are broadly classified based on their manufacturing method and their response to thermal treatments:

• Cast vs. Wrought Alloys:

• Wrought alloys are shaped by mechanical deformation processes such as rolling, extrusion, forging, or drawing. They are designated by the AA 1xxx through 8xxx series and account for the majority (approximately 85%) of aluminum usage.²
• Cast alloys are formed by pouring molten aluminum into molds. Common casting processes include sand casting, gravity die casting, and pressure die casting. Cast alloys, such as the LM series, ADC series, and AA xxx.x series, generally offer cost-effective production of complex shapes due to aluminum’s relatively low melting point, though they typically exhibit lower tensile strengths compared to wrought alloys.¹⁰
• Heat-Treatable vs. Non-Heat-Treatable Alloys:

• Heat-treatable alloys derive their strength from thermal processes. These processes involve solution heat treatment (heating to dissolve alloying elements into a solid solution), rapid cooling or quenching (to retain the supersaturated solution), and subsequent aging (natural or artificial/precipitation hardening) to precipitate fine intermetallic phases that impede dislocation movement and thus increase strength. Common heat-treatable wrought series include 2xxx (Al-Cu), 6xxx (Al-Mg-Si), and 7xxx (Al-Zn-Mg-Cu).² Many casting alloys, particularly those containing magnesium with silicon (Al-Si-Mg) or copper, are also heat-treatable.
• Non-heat-treatable alloys primarily achieve their strength through solid solution strengthening by alloying elements and strain hardening (cold working). The 1xxx (commercially pure Al), 3xxx (Al-Mn), and 5xxx (Al-Mg) wrought series are non-heat-treatable.² Some casting alloys also fall into this category.

1.4. Temper Designations

The properties of an aluminum alloy are profoundly influenced by its “temper,” which refers to the specific sequence of mechanical and/or thermal treatments it has undergone. The temper designation, an alphanumeric code appended to the alloy designation (e.g., 6061-T6), is therefore a critical part of the material specification.¹¹ An alloy designation without its temper is an incomplete specification, as a single alloy can exhibit a wide spectrum of mechanical properties depending on its processing history.

Key temper designations include:

• -F (As Fabricated): Applies to products formed without specific control over thermal conditions or strain hardening. Such materials often require further processing to achieve desired properties.²
• -O (Annealed): This temper indicates that the alloy has been heated to its lowest strength condition to maximize ductility and dimensional stability.²
• -H (Strain-Hardened): Used primarily for non-heat-treatable wrought alloys.

• H1x: Strain-hardened only. The second digit (x) indicates the degree of strain hardening (e.g., H18 for full-hard, H14 for half-hard).
• H2x: Strain-hardened and partially annealed.
• H3x: Strain-hardened and stabilized (by a low-temperature thermal treatment) to prevent age softening.³ The second digit from 1 to 8 typically indicates increasing amounts of cold work, with 8 representing the “maximum” commercially practical strain hardening and 9 exceeding these limits.¹¹
• -T (Thermally Treated): Applied to heat-treatable alloys that have undergone solution heat treatment followed by aging.

• T1: Cooled from an elevated temperature shaping process (e.g., extrusion) and naturally aged to a substantially stable condition.³
• T3: Solution heat-treated, cold worked (e.g., stretching or straightening to relieve stress and improve strength), and then naturally aged.³
• T4: Solution heat-treated and naturally aged to a substantially stable condition (without subsequent cold work).³
• T5: Cooled from an elevated temperature shaping process and then artificially aged (precipitation hardened at elevated temperature).³
• T6: Solution heat-treated and then artificially aged. This is a very common temper for achieving high strength in many 2xxx, 6xxx, and 7xxx series alloys.³ Additional digits after the primary T temper (e.g., T351, T651) indicate specific variations in processing, such as stress relief by stretching.¹¹

The existence of these diverse designation systems and the critical role of temper underscore the complexity of the aluminum alloy landscape. Effective material selection and application demand not only an understanding of an alloy’s nominal composition but also a precise awareness of its processing history as defined by its temper.

Table 1.1: Major Aluminum Alloy Designation Systems and Examples

Note: Examples are illustrative and equivalencies can be complex.

Section 2: Cast Aluminum Alloys: LM Series (British Standard BS 1490)

2.1. Introduction to LM Series

The LM series of aluminum casting alloys are designated under British Standard BS 1490. This standard specifies the chemical composition, including allowable trace elements, for a range of alloys primarily intended for various casting processes such as sand casting, gravity die casting (permanent mold), and pressure die casting.⁵ The choice of LM alloy is dictated by the required mechanical properties, casting characteristics, corrosion resistance, and end-use application. Many LM alloys are based on the aluminum-silicon system, often with additions of copper or magnesium to modify properties and enable heat treatment.⁵

2.2. Alloy LM0 (Al 99.5)

• Chemical Composition: LM0 is essentially commercially pure aluminum, with a minimum aluminum content of 99.5%. It is equivalent to ISO Al 99.5 and AA 150.⁵
  Table 2.2.1: Chemical Composition of LM0 (wt.%)

*Source: [14]*

• Mechanical Properties:
  Table 2.2.2: Mechanical Properties of LM0 (As-Cast)

*Source: [14]*

• Applications: Due to its high purity, LM0 offers excellent corrosion resistance and good electrical conductivity. It is used for electrical components, food processing equipment, and chemical plant applications where these properties are paramount.⁵

2.3. Alloy LM2 (Al-Si10Cu2Fe)

• Chemical Composition: A die-casting alloy, LM2 is characterized by high silicon and copper content. Its designation Al-Si10Cu2Fe reflects these primary additions.⁵ It has international equivalents such as ISO Al-Si10Cu2Fe, EN AC-46100, AA 384, and notably, JIS ADC12.⁵
  Table 2.3.1: Chemical Composition of LM2 (wt.%)

*Source: [15]*

• Mechanical Properties: LM2 is known for excellent castability suitable for pressure die casting.
  Table 2.3.2: Mechanical Properties of LM2 (Die Cast)

*Source: [15]*

• Applications: Primarily used for pressure die castings, including intricate engineering components where good die-filling characteristics are essential.⁵ Its applications are extremely varied and widespread.¹⁵

2.4. Alloy LM4 (Al-Si5Cu3)

• Chemical Composition: LM4 is an Al-Si-Cu alloy. Equivalents include ISO Al-Si5Cu3, approximately EN AC-45000, AA 319, and JIS AC2A.⁵
  Table 2.4.1: Chemical Composition of LM4 (wt.%)

*Source: [14, 16]*

• Mechanical Properties: LM4 is heat-treatable.
  Table 2.4.2: Mechanical Properties of LM4

*Source: [14, 16]*

• Applications: A versatile general engineering alloy suitable for both sand and die casting. It can form thick and thin sections and offers good pressure tightness.¹⁶ Commonly used for automotive components (manifolds, gearboxes, clutch cases, crankcases), switchgear covers, and tool handles.¹⁴ Its machinability is commendable, particularly after heat treatment.¹⁶

2.5. Alloy LM5 (Al-Mg5Si1)

• Chemical Composition: An Al-Mg alloy. International equivalents include ISO Al-Mg5Si1 (or AlMg6), approximately EN AC-51300, AA 514, and JIS AC7A.⁵
  Table 2.5.1: Chemical Composition of LM5 (wt.%)

*Source: [17, 18]*

• Mechanical Properties:
  Table 2.5.2: Mechanical Properties of LM5 (As-Cast)

*Source: [17, 18]*

• Applications: Used for sand and gravity die castings where high corrosion resistance is a primary requirement, especially in marine environments. Also found in food processing and chemical plant equipment.¹⁷

2.6. Alloy LM6 (Al-Si12 / Al-Si12Fe)

• Chemical Composition: LM6 is a near-eutectic Al-Si alloy. Equivalents include ISO Al-Si12(Fe), approximately EN AC-44100 (or EN AC-44000), AA A413, and JIS AC3A.⁵
  Table 2.6.1: Chemical Composition of LM6 (wt.%)

*Source: [14, 19]*

• Mechanical Properties (Typical, as-cast):
  Table 2.6.2: Mechanical Properties of LM6 (As-Cast)

*Source: [6]*
LM6 exhibits good castability, but its main advantage over some other Al-Si alloys like ADC12 lies in its wider solidification temperature range, allowing thicker sections to be cast without hot tearing defects. It also offers improved machinability compared to higher-copper Al-Si alloys due to its lower copper content.[7]

• Applications: Widely used for sand and gravity die castings, particularly for intricate shapes and thin sections such as manifolds, due to its excellent fluidity and corrosion resistance.⁵

2.7. Alloy LM9 (Al-Si10Mg)

• Chemical Composition: An Al-Si-Mg alloy. Equivalents are ISO Al-Si10Mg, approximately EN AC-43100 (or EN AC-43000), AA A360, and JIS AC4A.⁵
  Table 2.7.1: Chemical Composition of LM9 (wt.%)

*Source: [20, 21]*

• Mechanical Properties: LM9 is heat-treatable due to the magnesium content.⁵
  Table 2.7.2: Mechanical Properties of LM9

*Source: [20]* (*Note: M = As Cast, TE = Precipitation Heat Treated, TF = Fully Heat Treated*)

• Applications: Suitable for low-pressure die casting and other casting methods. Used for motor housings, cover plates, and other components where good castability and higher strength (after heat treatment) are needed.⁵

2.8. Alloy LM13 (Al-Si12CuNiMg)

• Chemical Composition: LM13 is a complex Al-Si alloy designed for high-temperature applications. It is equivalent to AA 336 and JIS AC8A.⁵ One source indicates the composition type as Al-Si12Cu2Mg1.²²
  Table 2.8.1: Chemical Composition of LM13 (wt.%) (Typical based on designation)

*Note: Specific ranges not detailed in provided sources. Designation Al-Si12CuFe also seen.[5, 6]*

• Mechanical Properties: Known for good strength and stability at elevated temperatures. Specific values are not provided.
• Applications: Primarily used for pistons in internal combustion engines, where it must withstand high operating temperatures and mechanical stresses.⁵

2.9. Alloy LM16 (Al-Si5Cu1Mg)

• Chemical Composition: An Al-Si-Cu-Mg alloy. Equivalents are AA 355 and JIS AC4D.⁵
  Table 2.9.1: Chemical Composition of LM16 (wt.%)

*Source: [14]*

• Mechanical Properties: Heat-treatable, offering good strength. Detailed mechanical properties are not listed in the provided sources, but it is similar in nature to other heat-treatable Al-Si-Cu-Mg alloys.
• Applications: Used for sand and chill (permanent mold) castings requiring good pressure tightness, such as cylinder heads and valve bodies.⁵

2.10. Alloy LM20 (Al-Si12Cu)

• Chemical Composition: An Al-Si-Cu alloy, often designated Al-Si12CuFe, with high silicon and a controlled copper addition.⁵ It is equivalent to JIS ADC12 according to one source.²³
  Table 2.10.1: Chemical Composition of LM20 (BS 1490) (wt.%)

*Source: [23]*

• Mechanical Properties:
  Table 2.10.2: Mechanical Properties of LM20 (As-Cast)

*Source: [23]*

• Applications: Used in pressure die casting for components requiring corrosion resistance, such as marine castings, water pumps, and meter cases.⁵

2.11. Alloy LM24 (Al-Si8Cu3Fe)

• Chemical Composition: A widely used Al-Si-Cu die-casting alloy. Equivalents include ISO Al-Si8Cu3Fe, approximately EN AC-46000 or EN AC-46500, AA A380, and JIS ADC10.⁵
  Table 2.11.1: Chemical Composition of LM24 (wt.%)

*Source: [19]*

• Mechanical Properties: (Properties are similar to AA A380 / JIS ADC10).
  Table 2.11.2: Mechanical Properties of EN AC-46500 (Close equivalent to LM24)

*Source: [24]*

• Applications: A general-purpose pressure die-casting alloy used for a vast range of engineering components, including crankcases, gearboxes, and other structural parts requiring good castability and moderate strength.⁵

2.12. Alloy LM25 (Al-Si7Mg0.5)

• Chemical Composition: A very popular Al-Si-Mg casting alloy. Equivalents are ISO Al-Si7Mg, EN AC-42100 or EN AC-42200, AA A356.0/A357.0, and JIS AC4C.⁵
  Table 2.12.1: Chemical Composition of LM25 (wt.%)

*Source: [14, 25]*

• Mechanical Properties: LM25 is highly responsive to heat treatment.
  Table 2.12.2: Mechanical Properties of LM25

*Source: [14, 25]*

• Applications: A general-purpose high-strength casting alloy with excellent castability and corrosion resistance. Widely used for automotive components (wheels, cylinder blocks, heads), marine castings, aerospace parts, and other structural applications where a good combination of strength and ductility is required.²⁵

2.13. Alloy LM27 (Al-Si7CuMn / Al-Si5Cu3)

• Chemical Composition: A versatile sand and chill casting alloy.
  Table 2.13.1: Chemical Composition of LM27 (wt.%)

*Source: [14]*

• Mechanical Properties:
  Table 2.13.2: Mechanical Properties of LM27

*Source: [14]*

• Applications: General engineering parts, good castability.⁵

2.14. Other LM Alloys

Other LM alloys mentioned include ²²:

• LM12 (Al-Cu10Mg0.3): A heat-treatable alloy known for good machinability, used for hydraulic equipment.⁵
• LM21 (Al-Si6Cu4Mn0.4Mg0.2): Similar to LM4, used for sand and gravity castings like crankcases and gearboxes.⁵
• LM22 (Al-Si5Cu3Mn0.4): A chill-cast version, solution treated for good shock resistance, used in automotive heavy-duty parts.⁵
• LM26 (Al-Si10Cu3Mg1): Used for chill-cast pistons.⁵
• LM28 (Al-Si18Cu1.5Mg1Ni1): High-performance piston alloys.⁵
• LM29 (Al-Si23Cu1Mg1Ni1): High-performance piston alloys.⁵
• LM30 (Al-Si17Cu4.5Mg0.5): A hypereutectic Al-Si alloy (similar to AA 390) used for pressure die-cast unlined cylinder blocks due to its excellent wear resistance.⁵
• LM31 (Al-Zn5Mg0.7Cr0.5Ti): A high-strength, self-aging sand casting alloy with good shock resistance, suitable for large castings.⁵

The prevalence of silicon as a primary alloying element across the LM series, often complemented by copper and/or magnesium, underscores the importance of the Al-Si system in achieving desirable casting characteristics and a wide range of mechanical properties. Silicon’s role in enhancing fluidity is fundamental to casting processes.¹² The addition of magnesium (as in LM9, LM25) or copper (as in LM4, LM12) allows for heat treatment, leading to significant strength improvements through precipitation hardening. This makes alloys like LM25 exceptionally versatile, suitable for moderately stressed applications in the as-cast state or for high-performance components when fully heat-treated. This adaptability, however, is temperature-dependent, as prolonged exposure to elevated temperatures can negate the benefits of heat treatment for certain alloys.²⁵ The specific combination of these elements tailors each LM alloy for particular end-uses, from general engineering components (LM4) to corrosion-resistant marine parts (LM5) or specialized applications like pistons (LM13, LM28, LM29).

Table 2.1: Summary of Key LM Series Aluminum Casting Alloys

Section 3: Cast Aluminum Alloys: ADC Series (Japanese Industrial Standard JIS)

3.1. Introduction to ADC Series

The ADC series of aluminum alloys are designated under Japanese Industrial Standards (JIS H 5302) and are specifically formulated for die-casting applications.⁷ The nomenclature “ADC” signifies Aluminum Die Casting, with the subsequent number identifying the specific alloy composition.⁸ These alloys are characterized by excellent fluidity and castability, making them suitable for producing complex, thin-walled components at high production rates, typical of the high-pressure die-casting process.⁷

3.2. Alloy ADC1 (JIS H 5302)

• Chemical Composition: ADC1 is an Al-Si eutectic or near-eutectic alloy.
  Table 3.2.1: Chemical Composition of ADC1 (wt.%)

*Source:*

• Mechanical Properties & Applications: Its high silicon content suggests excellent fluidity, making it suitable for intricate die castings where mechanical strength requirements are moderate.
  Table 3.2.2: Mechanical Properties of ADC1

*Note: Property values can vary between sources and test conditions.*

3.3. Alloy ADC3 (JIS H 5302)

• Chemical Composition: ADC3 is an Al-Si-Mg type alloy.
  Table 3.3.1: Chemical Composition of ADC3 (wt.%)

*Source: [19, 26]*

• Mechanical Properties & Applications: The magnesium addition suggests some potential for strengthening. Used where high impact resistance and corrosion resistance are needed.
  Table 3.3.2: Mechanical Properties of ADC3

*Note: Property values can vary between sources and test conditions.*

3.4. Alloy ADC10 (JIS H 5302)

• Chemical Composition: ADC10 is an Al-Si-Cu alloy, very similar in composition to AA A380 and LM24.
  Table 3.4.1: Chemical Composition of ADC10 (wt.%)

*Source: [19, 26]*

• Mechanical Properties: Properties are comparable to AA A380 and LM24.
  Table 3.4.2: Mechanical Properties of ADC10 (Typical, similar to A380/EN AC-46500)

*Source:*

• Applications: A very common general-purpose die-casting alloy used for a wide variety of engineering components, similar to LM24 and A380.⁵

3.5. Alloy ADC12 (JIS H 5302)

• Chemical Composition: ADC12 is a widely used Al-Si-Cu die-casting alloy, also known as Aluminum 383 in the AA system and having similarities to LM2.⁵
  Table 3.5.1: Chemical Composition of ADC12 (wt.%)

*Source: [8, 19, 26, 27]*

• Mechanical Properties (Typical for die-cast ADC12 / AA 383):
  Table 3.5.2: Mechanical Properties of ADC12 (AA 383)

*Source:*

• Features & Applications: ADC12 is renowned for its excellent castability and fluidity.⁷ Extensive use in automotive components, consumer electronics housings, industrial parts, and building/construction elements.⁸

3.6. Other ADC Alloys

The JIS system includes other ADC alloys with varying compositions ¹⁹:

• ADC5: Al-Mg type (Mg 4.0–8.5%, Si 0.3% max).
• Mechanical Properties (Typical): Tensile Strength ~309 MPa, Shear Strength ~196 MPa.

• ADC6: Al-Mg-Mn type (Mg 2.5–4.0%, Mn 0.4–0.6%, Si 1.0% max).
• ADC10Z / ADC12Z: Variants of ADC10 and ADC12 with higher Zinc (Zn up to 3.0%).
• ADC14: Hypereutectic Al-Si alloy (Si 16.0–18.0%, Cu 4.0–5.0%, Mg 0.45–0.65%).

The ADC series, particularly the workhorses ADC10 and ADC12, exemplifies alloys engineered for the demands of high-pressure die casting. Their compositions, rich in silicon for fluidity and often copper for strength and enhanced die-filling, facilitate the mass production of complex, near-net-shape parts. This focus on castability is a defining characteristic. However, this specialization involves trade-offs; for instance, the copper that boosts ADC12’s strength can make it slightly less machinable and does not confer significant corrosion advantages over lower-copper alloys.⁷ Furthermore, the presence of elements like iron, often carried over from recycled aluminum or inherent in the alloying process, must be carefully managed as they can form detrimental intermetallic phases if levels are too high.⁸ The international recognition and equivalency of alloys like ADC10 (as AA A380 or LM24) and ADC12 (as AA 383/384 or approximately LM2) attest to their optimized balance of properties and widespread adoption in global manufacturing.⁵

Table 3.1: Summary of Key ADC Series Aluminum Die-Casting Alloys

Section 4: Cast Aluminum Alloys: AS7G, AS7U, AS9 and Related Al-Si Compositions

4.1. Understanding French (AFNOR) and Al-Si Designations

French standards for aluminum alloys, historically under AFNOR, often use designations beginning with ‘A’, followed by chemical symbols and numbers indicating percentages or a specific grade. For instance, ‘A-S7G’ denotes an aluminum (A) – silicon (S) alloy with approximately 7% Si and magnesium (G).⁹ The initial digit following ‘A’ in some AFNOR numerical systems can also signify the primary alloying group (e.g., 4 for Si-based, 5 for Mg-based).⁹ The ‘AS’ prefix generally points to an Aluminum-Silicon base. Within this system, ‘G’ commonly implies a magnesium addition, and ‘U’ often indicates copper.

4.2. Alloy AS7G (AlSi7Mg type)

• Designation Context: AS7G is a widely recognized French designation for Al-Si7Mg type alloys, closely related or equivalent to alloys like AA A356.0, AA A357.0, and BS LM25.²⁸ A 356.0 is referred to as AS7G 03, and EN AC-AlSi7Mg0,6 (similar to A357.0) as AS7G 06.²⁸
• Chemical Composition (Typical for AlSi7Mg / AS7G type):
  Table 4.2.1: Chemical Composition of AS7G (AlSi7Mg type) (wt.%)

*Source: [25, 29, 30]*

• Mechanical Properties (Heat-Treatable, T6 condition is common):
  Table 4.2.2: Mechanical Properties of AS7G (AlSi7Mg type)

*Source: [25, 29, 30, 31]*

• Applications: AS7G type alloys are workhorses for high-integrity castings requiring an excellent combination of strength, ductility, good fatigue resistance, pressure tightness, and good castability. They are extensively heat-treated (typically to a T6 temper) to achieve optimal properties. Common applications include aerospace components (aircraft frames, landing gear parts, structural elements), automotive parts (engine components, cylinder heads, wheels, suspension parts), and consumer electronics (heat sinks, structural housings).²⁵

4.3. Alloy AS7U (Interpretation and Related Alloys)

• Designation Challenge: Specific and unambiguous datasheet information for an alloy singularly designated “AS7U” is not readily available in the provided resources. In French casting alloy nomenclature, the letter ‘U’ typically signifies a copper (Cu) addition.⁵ Therefore, “AS7U” would logically imply an Al-Si7-Cu type alloy.
• Possible Interpretations/Related Alloys: No direct match for “AS7U” with Si ~7% and Cu as the main secondary element is clearly identified.
• Conclusion: Due to the lack of specific data for “AS7U,” this report cannot provide detailed chemical and mechanical properties for it.

4.4. Alloy AS9

The designation “AS9” appears to have at least two distinct interpretations.

Interpretation 1: AS9 as Al-Si-Cu-Ni-Mg Alloy (Piston Alloy Type)

• Chemical Composition:
  Table 4.4.1: Chemical Composition of AS9 (Piston Alloy Type, wt.%)

*Source: [19, 26, 32]*

• Mechanical Properties: Specific mechanical property data for this exact AS9 composition is not detailed. Alloys of this type are typically heat-treatable and designed for good strength, wear resistance, and stability at moderately elevated temperatures.
• Applications: Piston ring carriers, components for internal combustion engines.³²

Interpretation 2: AS9 related to AlSi9Mg Alloys

• Chemical Composition (AlSi9Mg type, e.g., EN AC-43300):
  Table 4.4.2: Chemical Composition of AS9 (AlSi9Mg type, wt.%)

*Source: [19, 33, 34]*

• Mechanical Properties (Heat-Treated, e.g., T6 condition for AlSi9Mg):
  Table 4.4.3: Mechanical Properties of AS9 (AlSi9Mg type)

*Source: [33, 34, 35]*

• Applications: Automotive components, aerospace structural parts, industrial equipment, consumer electronics.³⁴

The clear utility of AS7G (AlSi7Mg, A356 equivalent) as a high-performance, heat-treatable casting alloy is evident from its application in demanding sectors like aerospace and automotive.28 The magnesium addition to the Al-Si base is pivotal, enabling significant strengthening through the precipitation of Mg$_2$Si during heat treatment.12 This makes AS7G a reliable choice for components needing a good balance of strength, ductility, and castability.

Conversely, the designations AS7U and AS9 highlight potential ambiguities in alloy specification. The absence of direct, readily available data for a unique “AS7U” alloy underscores the challenge that can arise with less common or poorly documented designations. For “AS9,” the existence of at least two distinct chemical compositions (an Al-Si-Cu-Ni-Mg type for high-temperature applications 19 and the more common AlSi9Mg family 19) emphasizes the critical need for referencing full chemical specifications or specific international standards (like EN AC-xxxxx) rather than relying on abbreviated or potentially ambiguous local terms. This is particularly important when minor alloying elements, such as nickel in the piston-type AS9, are added to impart specialized properties like enhanced high-temperature strength and wear resistance, differentiating them from simpler AlSiMg alloys.32

Table 4.1: Summary of Key AS7G (AlSi7Mg type) and AS9 (Potential Variants) Aluminum Casting Alloys

Section 5: Wrought Aluminum Alloys: Properties and Applications of Key Series

5.0. Introduction to Wrought Alloy Series (1xxx-8xxx)

Wrought aluminum alloys are designated by a four-digit system established by The Aluminum Association (AA), where the first digit indicates the principal alloying element or group ²:

• 1xxx Series: Commercially pure aluminum (minimum 99.0% Al).
• 2xxx Series: Copper is the principal alloying element.
• 3xxx Series: Manganese is the principal alloying element.
• 4xxx Series: Silicon is the principal alloying element.
• 5xxx Series: Magnesium is the principal alloying element.
• 6xxx Series: Magnesium and silicon are the principal alloying elements.
• 7xxx Series: Zinc is the principal alloying element.
• 8xxx Series: Alloying elements other than those above.

5.1. Alloy 2024 (Al-Cu-Mg)

• Chemical Composition:
  Table 5.1.1: Chemical Composition of Alloy 2024 (wt.%)

*Source: [36, 37]*

• Mechanical Properties (Typical for 2024-T4/T351):
  Table 5.1.2: Mechanical Properties of Alloy 2024 (T4/T351 Temper)

*Source: [36, 37]*

• Characteristics: High strength-to-weight ratio, good machinability.³⁶ Lower corrosion resistance, often requiring cladding or coating.² Welding can be challenging.³⁶
• Applications: Aerospace structural components, military equipment, truck wheels, bolts, pistons, gears.³⁶

5.2. Alloy 5754 (Al-Mg)

• Chemical Composition:
  Table 5.2.1: Chemical Composition of Alloy 5754 (wt.%)

*Source: [38, 39]*

• Mechanical Properties (Typical for 5754-H111 sheet, 0.2mm to 6.00mm):
  Table 5.2.2: Mechanical Properties of Alloy 5754 (H111 Temper)

*Source: [38, 39]*

• Characteristics: Excellent corrosion resistance (especially seawater), higher strength than 5251. Excellent weldability, very good cold workability.³⁸
• Applications: Flooring (treadplate), shipbuilding, vehicle bodies, rivets, fishing industry equipment, food processing machinery, welded chemical/nuclear structures.³⁸

5.3. Alloy 6061 (Al-Mg-Si)

• Chemical Composition:
  Table 5.3.1: Chemical Composition of Alloy 6061 (wt.%)

*Source: [40, 41]*

• Mechanical Properties (Typical for 6061-T6/T651):
  Table 5.3.2: Mechanical Properties of Alloy 6061 (T6/T651 Temper)

*Source: [40, 41]*

• Characteristics: Versatile, good strength, excellent corrosion resistance, good weldability and machinability. Excellent joining and coating acceptance.⁴⁰
• Applications: Structural components, automotive parts, aircraft/marine fittings, electrical connectors, valves, architectural uses.⁴⁰

5.4. Alloy 6063 (Al-Mg-Si)

• Chemical Composition:
  Table 5.4.1: Chemical Composition of Alloy 6063 (wt.%)

*Source: [42, 43]*

• Mechanical Properties (Typical for 6063-T6 extrusions):
  Table 5.4.2: Mechanical Properties of Alloy 6063 (T6 Temper Extrusions)

*Source: [42, 43]*

• Characteristics: “Architectural alloy,” excellent surface finish, high suitability for anodizing. Medium strength, excellent corrosion resistance, very good extrudability.⁴²
• Applications: Architectural (window/door frames, curtain walls), extrusions, irrigation tubing, electrical enclosures, heat sinks, furniture, railings.⁴²

5.5. Alloy 6082 (Al-Mg-Si-Mn)

• Chemical Composition:
  Table 5.5.1: Chemical Composition of Alloy 6082 (wt.%)

*Source: [44, 45]*

• Mechanical Properties (Typical for 6082-T6/T651 plate, 6.00mm to 12.5mm thickness):
  Table 5.5.2: Mechanical Properties of Alloy 6082 (T6/T651 Temper Plate)

*Source: [44, 45]*

• Characteristics: Highest strength 6xxx alloy, excellent corrosion resistance, good weldability and machinability.⁴⁴
• Applications: Highly stressed structures, trusses, bridges, cranes, transport applications.⁴⁴

5.6. Alloy 7075 (Al-Zn-Mg-Cu)

• Chemical Composition:
  Table 5.6.1: Chemical Composition of Alloy 7075 (wt.%)

*Source:*

• Mechanical Properties (Typical for 7075-T6):
  Table 5.6.2: Mechanical Properties of Alloy 7075 (T6 Temper)

*Source:*

• Characteristics: Very high strength, good machinability. Lower corrosion resistance (SCC susceptibility in T6). T73 temper improves SCC resistance.
• Applications: Aerospace/defense (aircraft structures, missile parts), high-performance sporting equipment.

The selection among these wrought alloys demonstrates a clear linkage between their primary alloying elements and their resultant properties. For instance, the 2xxx series, rich in copper, and the 7xxx series, dominated by zinc, are chosen for applications demanding the highest strength, such as aerospace structures.³ Conversely, the 5xxx series, with magnesium as its key addition, excels in environments requiring superior corrosion resistance, like marine applications, and offers good weldability.³⁸ The 6xxx series alloys, such as 6061 and 6063, represent a versatile middle ground, balancing moderate to good strength with good corrosion resistance, weldability, formability, and excellent extrudability. This makes them ubiquitous in a wide array of applications, from structural members to intricate architectural profiles.⁴⁰ Alloy 6082 further enhances the strength capabilities within the 6xxx family, often replacing 6061 in more demanding structural roles.⁴⁴

However, achieving high strength, particularly in the 2xxx and 7xxx series, often involves trade-offs. These high-strength alloys typically exhibit reduced corrosion resistance compared to the 5xxx or 6xxx series and can present greater challenges in welding. This necessitates careful design considerations, which may include protective coatings, cladding (like Alclad for 2024), or selection of specific tempers (like T73 for 7075 to improve stress corrosion cracking resistance).² As with cast alloys, the temper designation for wrought alloys is of paramount importance. For heat-treatable alloys, tempers like -T6 or -T4 are essential for developing their full strength potential, while for non-heat-treatable alloys like 5754, the -H series tempers define the degree of strain hardening and thus the final mechanical properties.³

Table 5.1: Alloy 2024 – Chemical Composition, Mechanical Properties (T4/T351 Temper), and Applications

Table 5.2: Alloy 5754 – Chemical Composition, Mechanical Properties (H111 Temper), and Applications

Table 5.3: Alloy 6061 – Chemical Composition, Mechanical Properties (T6/T651 Temper), and Applications

Table 5.4: Alloy 6063 – Chemical Composition, Mechanical Properties (T6 Temper), and Applications

Table 5.5: Alloy 6082 – Chemical Composition, Mechanical Properties (T6/T651 Temper), and Applications

Table 5.6: Alloy 7075 – Chemical Composition, Mechanical Properties (T6 Temper), and Applications

Section 6: General Overview of Al-Si (Aluminum-Silicon) Alloy Systems

6.1. Significance of Al-Si Alloys

Aluminum-silicon (Al-Si) alloys, often referred to by the general term “Silumin,” constitute the most important and widely used group of aluminum casting materials.¹³ Their prominence stems primarily from the excellent casting characteristics imparted by silicon. Silicon additions typically range from 3% to 25% by weight in commercial casting alloys, although specialized powder metallurgy Al-Si alloys can contain up to 50% Si.¹² The primary benefits of silicon include enhanced fluidity of the molten metal, reduced solidification shrinkage, and improved resistance to hot tearing, all of which facilitate the production of sound and intricate castings.¹²

6.2. The Al-Si Phase Diagram and Eutectic

The binary Al-Si system is characterized by a simple eutectic phase diagram.¹²

• The eutectic reaction (Liquid → α-Al + Si) occurs at a specific composition and temperature. The accepted eutectic composition is approximately 12.5–12.6 wt% silicon, and the eutectic temperature is around 577°C.¹²
• The solid solubility of silicon in aluminum is limited. At the eutectic temperature, aluminum can dissolve up to 1.65 wt% Si. This solubility decreases rapidly with decreasing temperature, becoming negligible at room temperature (e.g., only 0.05% Si at 250°C).¹² Conversely, aluminum is practically insoluble in silicon. This limited solid solubility means that strengthening through solid solution hardening by silicon is minimal in binary Al-Si alloys. The primary microstructural constituents are the aluminum-rich solid solution (α-Al) and elemental silicon particles.

6.3. Influence of Silicon Content on Properties

The amount of silicon significantly influences both the castability and the final properties of Al-Si alloys:

• Castability: As silicon content increases up to and beyond the eutectic composition, the fluidity of the molten alloy generally improves. Mold filling capacity reaches its maximum at around 12% Si and remains good at other levels. The tendency to form shrinkage cavities is lowest between 6% and 8% Si. Resistance to hot cracking is generally good, particularly for alloys with less than 6% Si.¹³
• Mechanical Properties: The best combination of mechanical properties in binary Al-Si alloys is typically found in the range of 6% to 12% Si.¹³ Pure Al-Si alloys are not hardenable by heat treatment but offer medium strength and good corrosion resistance, even in saline environments.¹³
• Wear Resistance: In hypereutectic alloys (those with Si content greater than the eutectic, >12.6%), primary silicon particles form during solidification. These hard Si particles significantly improve the alloy’s wear resistance, making such alloys suitable for applications like engine blocks and pistons.¹²

6.4. Classification based on Si Content

Al-Si alloys are commonly classified based on their silicon content relative to the eutectic composition:

• Hypoeutectic Alloys (<12.6% Si): Solidify with primary dendrites of α-Al, followed by the Al-Si eutectic filling the interdendritic spaces.
• Eutectic Alloys (~12.6% Si): Solidify with a microstructure predominantly composed of the Al-Si eutectic.
• Hypereutectic Alloys (>12.6% Si): Solidify with primary silicon particles (often coarse and acicular in unmodified alloys) embedded in a eutectic matrix.

6.5. Modification and Grain Refinement

The morphology and size of the silicon particles, as well as the grain size of the α-Al matrix, profoundly affect the mechanical properties, especially ductility and toughness.

• Modification: The eutectic silicon in unmodified Al-Si alloys typically forms as coarse, interconnected plates, which can act as stress concentrators and limit ductility. Modification, achieved by adding small amounts of elements like sodium (Na) or strontium (Sr), alters the growth of eutectic silicon from acicular plates to a fine, fibrous, or lamellar morphology. This refinement of the eutectic silicon significantly improves ductility, toughness, and strength.¹² Sodium modification has been known since the 1920s.¹²
• Refinement of Primary Silicon: In hypereutectic alloys, the primary silicon particles can also be coarse. Phosphorus (P) additions are effective in refining these primary Si particles, reducing their size and promoting a more uniform distribution, which enhances machinability and mechanical properties.¹²
• Grain Refinement of α-Aluminum: Adding grain refiners, typically containing titanium (Ti) and boron (B) (often as Al-Ti-B master alloys), promotes the formation of finer α-Al grains during solidification. Finer grains lead to improved strength, ductility, and feeding characteristics during casting.

6.6. Common Alloying Additions to Al-Si Base

While binary Al-Si alloys have good casting properties, their mechanical strength is often insufficient for many engineering applications. Alloying with other elements, particularly copper and magnesium, allows for heat treatment and significantly enhanced mechanical properties:

• Copper (Cu): Addition of copper (typically 1-5%) to Al-Si alloys (forming Al-Si-Cu alloys like LM4, ADC10, ADC12) increases strength and hardness, both in the as-cast condition and particularly after heat treatment (precipitation of Al$_2$Cu and related phases). Copper can also improve machinability. However, copper additions generally reduce corrosion resistance and can sometimes decrease ductility.¹³
• Magnesium (Mg): Magnesium (typically 0.2-0.7%) added to Al-Si alloys (forming Al-Si-Mg alloys like LM9, LM25, AS7G/A356) enables significant strengthening through age hardening. During heat treatment, magnesium combines with silicon to form fine precipitates of magnesium silicide (Mg$_2$Si), which are very effective strengtheners.¹³ These alloys often exhibit a good combination of strength, ductility, and corrosion resistance.
• Iron (Fe): Iron is a common and often detrimental impurity in aluminum alloys, typically originating from raw materials or melting equipment. In Al-Si alloys, iron can form brittle, needle-like or plate-like intermetallic phases (e.g., β-Al$_9$Fe$_2$Si or β-Al$_5$FeSi), which can severely reduce ductility and fracture toughness.¹² The harmful effects of iron can be mitigated to some extent by controlling its level, by rapid solidification (in die casting), or by adding elements like manganese, which can modify the Fe-rich intermetallics into less harmful, more compact “Chinese script” morphologies.
• Manganese (Mn) and Chromium (Cr): Besides modifying Fe intermetallics, Mn can contribute to strength and improve high-temperature properties. Cr can also enhance strength and corrosion resistance in some alloys.
• Nickel (Ni) and Zinc (Zn): Nickel can improve strength at elevated temperatures and wear resistance (e.g., in piston alloys). Zinc can increase strength and improve castability in some die-casting alloys but may reduce corrosion resistance if present in large amounts.

The Al-Si alloy system’s dominance in casting is a direct result of silicon’s profound ability to improve fluidity and reduce casting defects, which are fundamental for producing complex shapes.¹³ The eutectic nature of the Al-Si phase diagram is central to this behavior. However, the utility of these alloys extends far beyond binary compositions. The ability to engineer the microstructure through modification (e.g., with Na or Sr to refine eutectic Si) and grain refinement (e.g., with Ti and B for α-Al) is crucial for optimizing mechanical properties, particularly ductility and toughness, by controlling the size and morphology of the Si phase.¹² Furthermore, the synergistic addition of elements like copper and magnesium transforms the basic Al-Si platform into heat-treatable systems (Al-Si-Cu and Al-Si-Mg). This allows for a significant expansion of their strength capabilities through precipitation hardening mechanisms, making them suitable for a much wider range of structural and engineering applications than binary Al-Si alloys alone could address.¹³ This combination of excellent castability from silicon and enhanced mechanical properties from other alloying elements and heat treatment underpins the versatility and widespread use of Al-Si based casting alloys.

Table 6.1: Influence of Silicon Content and Key Additives on Al-Si Alloy Characteristics

Section 7: Understanding ‘A’ and ‘Al’ Prefixes in Alloy Designations

The prefixes ‘A’ and ‘Al’ in aluminum alloy designations are not arbitrary; they serve as key identifiers for specific international and regional nomenclature systems. Understanding their context is crucial for correctly interpreting alloy specifications.

7.1. ‘A’ Prefix – Unified Numbering System (UNS)

As introduced in Section 1.2, the Unified Numbering System (UNS), widely used in North America, employs a single-letter prefix to denote the broad family of metals. For aluminum and its alloys, this prefix is ‘A’.⁴ This letter is followed by five digits, which often (but not always) have a direct correlation with the four-digit designations of The Aluminum Association (AA). For example:

• AA6061 is equivalent to UNS A96061
• AA2024 is equivalent to UNS A92024
• AA7075 is equivalent to UNS A97075.¹ The UNS system provides a concise and standardized numerical identifier, facilitating database management and cross-referencing, particularly with the prevalent AA system.

7.2. ‘Al’ Prefix – International Organization for Standardization (ISO)

The International Organization for Standardization (ISO) uses the chemical symbol ‘Al’ as a prefix for its aluminum alloy designation system, also detailed in Section 1.2. This prefix is immediately followed by the chemical symbols of the main alloying elements and their nominal percentages (rounded or as ranges).⁴ Examples include:

• AA6061 is equivalent to ISO AlMg1SiCu
• AA6063 is equivalent to ISO AlMg0.5Si
• AA2024 is equivalent to ISO AlCu4Mg1
• AA7075 is equivalent to ISO AlZn6MgCu.¹ This ISO nomenclature is highly descriptive, offering immediate qualitative and semi-quantitative information about an alloy’s primary constituents. This can be particularly useful for materials scientists and engineers to quickly understand the alloy family and anticipate its general characteristics (e.g., heat-treatability, expected strength level, corrosion behavior) without needing to consult a separate database. However, for alloys with many significant alloying elements, this designation can become lengthy. It is more frequently encountered in academic literature and research papers than in industrial part specifications or drawings.¹

7.3. Other Uses or Contexts

Beyond these formal designation systems:

• General Abbreviation: ‘Al’ is the universal chemical symbol for the element aluminum. As such, it is commonly used in scientific texts, technical reports, and general engineering discourse to refer to aluminum-based materials in a broad sense (e.g., “Al alloys exhibit good conductivity,” “Al matrix composites”).
• AFNOR (French Standards): Some French standards for aluminum alloys, under AFNOR, also begin with the letter ‘A’ (representing Aluminium), followed by letters and numbers indicating the chemical composition (e.g., A-S7G for an Al-Si-Mg alloy, A-U4G1 for an Al-Cu-Mg alloy like 2024).⁹

The prefixes ‘A’ (UNS) and ‘Al’ (ISO) thus serve as important flags, signaling the specific designation system being employed. While the UNS ‘A’ system offers a concise numerical code often linked to the widely adopted AA system, facilitating industrial standardization and lookup, the ISO ‘Al’ system provides a more descriptive chemical summary. This descriptive nature allows for an immediate, albeit general, understanding of an alloy’s type and potential properties based on its listed constituents. Both systems contribute to the broader framework of identifying and classifying the diverse range of aluminum alloys used globally.

Section 8: Summary and Key Considerations for Alloy Selection

This report has detailed the chemical compositions, mechanical properties, and applications of a range of aluminum alloys, encompassing British Standard LM series, Japanese Industrial Standard ADC series, French AS-designated casting alloys, key wrought alloy series (2024, 5754, 6061, 6063, 6082, 7075), and the fundamental principles of Al-Si alloy systems. The information presented highlights the vast diversity within aluminum metallurgy, driven by the need to tailor materials for specific performance requirements and manufacturing processes.

8.1. Recapitulation of Alloy Systems Covered

• LM Series (BS 1490 Casting Alloys): A diverse group, predominantly Al-Si based, with additions like Cu and Mg for enhanced properties and heat treatability (e.g., LM4, LM6, LM25).
• ADC Series (JIS Die-Casting Alloys): Specifically designed for high-pressure die casting, emphasizing fluidity and castability, with ADC10 and ADC12 (Al-Si-Cu types) being prominent.
• AS-Designated Casting Alloys: French nomenclature, with AS7G (Al-Si-Mg, similar to A356) being a key high-performance alloy, and AS9 having multiple interpretations (e.g., Al-Si-Cu-Ni-Mg or Al-Si-Mg).
• Wrought Alloy Series (AA Designations):

• 2024 (Al-Cu-Mg): High-strength aerospace alloy.
• 5754 (Al-Mg): Excellent corrosion resistance, good for marine applications.
• 6061, 6063, 6082 (Al-Mg-Si): Versatile, heat-treatable alloys with a good balance of properties, widely used in structural and architectural applications.
• 7075 (Al-Zn-Mg-Cu): Very high-strength aerospace alloy.
• Al-Si Alloy Systems: The foundational casting alloy system, leveraging silicon for castability and often modified with Mg or Cu for strength.

8.2. Key Factors Influencing Alloy Selection

The choice of an aluminum alloy for a specific application is a multifaceted decision, balancing performance requirements, manufacturability, and economic considerations. No single alloy is optimal for all purposes. Key factors include:

• Manufacturing Process:

• Casting: Al-Si based alloys (LM, ADC, AS series) are generally preferred due to their superior castability. Specific alloys are optimized for different casting methods: ADC12 for high-pressure die casting due to high fluidity ⁷; LM25 or AS7G for sand or gravity die casting, especially when heat treatment is required for high integrity parts.²⁵
• Wrought Processing: The 1xxx-8xxx series alloys are designed for processes like extrusion (e.g., 6063 for complex profiles ⁴²), rolling (e.g., 5754 for sheet/plate ³⁸), or forging (e.g., 2024, 7075 for high-strength components).
• Mechanical Properties Required:

• Strength (Tensile, Yield, Fatigue): For the highest strength in wrought forms, 7xxx (e.g., 7075-T6) and 2xxx (e.g., 2024-T4 ³⁶) series are primary choices. For high-strength castings, heat-treated Al-Si-Mg alloys like LM25-TF or AS7G-T6 are selected.²⁵
• Ductility/Formability: Alloys with lower strength, such as the 5xxx series (e.g., 5754-O) or 6063 in the T4 temper, generally offer better ductility and formability.³⁸
• Hardness/Wear Resistance: Hypereutectic Al-Si alloys (e.g., ADC14, LM30 ⁵) and specialized compositions like the Cu-Ni bearing AS9 variant are used for applications demanding wear resistance.
• Corrosion Resistance:

• The 5xxx series wrought alloys (e.g., 5754 ³⁸) and high-purity aluminum (1xxx series, LM0 ⁵) offer the best general corrosion resistance, especially in marine or aggressive chemical environments. The 6xxx series (e.g., 6061, 6063) also provides good corrosion resistance.⁴⁰
• Alloys with high copper content, such as the 2xxx series and many 7xxx series alloys, generally exhibit lower corrosion resistance and may require protective coatings or cladding.
• Weldability:

• The 5xxx and 6xxx series wrought alloys are generally considered to have good to excellent weldability.³⁸
• High-strength alloys like the 2xxx and 7xxx series can be more challenging to weld, often requiring specialized techniques and sometimes resulting in reduced joint efficiency or susceptibility to cracking.
• Machinability:

• Alloys like 2024 are known for good machinability.³⁷ 6061-T6 also machines well.⁴⁴
• High-silicon cast alloys can be more abrasive to cutting tools, although specific grades like LM6 are noted for better machinability than some higher-copper Al-Si alloys like ADC12.⁷
• Operating Temperature:
• Most standard aluminum alloys lose significant strength at elevated temperatures (e.g., above 150-200°C). Specialized alloys, such as LM13 or the piston-type AS9 (with Ni), are designed for improved performance at higher service temperatures.³² The benefits of heat treatment in alloys like LM25 can diminish with prolonged exposure to temperatures around 130°C or higher.²⁵
• Surface Finish and Anodizing Quality:
• Alloy 6063 is particularly renowned for its ability to achieve an excellent surface finish after extrusion and its suitability for decorative and protective anodizing.⁴²
• Cost:
• General-purpose die-casting alloys like ADC10/A380 and ADC12 are often cost-effective for high-volume production due to efficient processing and material availability. The cost of wrought alloys varies significantly based on composition, processing complexity, and production volume.

The extensive range of aluminum alloys has been developed precisely because no single alloy can meet the diverse and often conflicting demands of modern engineering. The selection process invariably involves navigating trade-offs – for example, the pursuit of maximum strength in alloys like 7075 often comes at the cost of reduced corrosion resistance and weldability when compared to more ductile or corrosion-resistant alloys like 5754. Understanding the broad characteristics of an alloy family (e.g., Al-Mg wrought alloys for corrosion resistance, Al-Si-Mg cast alloys for heat-treatable strength) provides a valuable starting point. However, the final material choice must drill down to a specific alloy grade and, crucially, its temper. The temper designation is not an afterthought but an integral part of the material specification, as it dictates the microstructure and, consequently, the final mechanical properties (e.g., the significant strength difference between LM25-M and LM25-TF ²⁵, or between 7075-T6 and 7075-O).

8.3. Importance of Cross-Checking and Using Reputable Data

Given the multiplicity of international and national standards, and the subtle but significant variations in properties that can arise from minor compositional differences or processing history, it is imperative to use precise alloy specifications, including the temper. Data should be sourced from recognized standards bodies (e.g., AA, EN, ISO, JIS, BS) or reputable material suppliers’ certified datasheets. Typical property values provided in general handbooks or even some standards (as indicated by “NOT FOR DESIGN” notes on some AA data ³⁷) should be treated with caution for critical design calculations. For demanding applications, independent verification of properties or consultation with materials experts is advisable. The consistent and accurate application of aluminum alloy knowledge is key to successful engineering outcomes.

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