Aluminium Alloy Designations, Properties, and Applications

Executive Summary

On an engineering bill of materials, “6061-T6” and “7075-T651” look like a trivial difference in digits. In practice they describe two materials whose tensile strengths differ by nearly a factor of two, whose weldability ranges from “excellent” to “not recommended,” and whose cost differs by two to three times. Specifying the wrong grade can mean scrapping an entire heat of material—or, at worst, a structural component failing in service by stress-corrosion cracking.

The confusion surrounding aluminum alloy designations stems from several standards running in parallel worldwide. The four-digit system of the Aluminum Association (AA) is the most widely used international language. China’s GB standard maintains a legacy set of letter codes (LF, LY, LC, LD) alongside modern designations such as 2A12 and 5A06.

Japanese JIS prefixes the AA number with the letter A, yielding forms like A6061. European EN standards write EN AW-6061. One material therefore carries four different names across four systems, and procurement and technical communication break down easily.

This document is written for engineering material selection. It first establishes the rules for reading designations, then compares properties series by series, and finally provides actionable selection guidance together with commonly encountered misconceptions. All mechanical property values are minimum guaranteed values taken from the respective national standards. Actual purchases should always be confirmed against the supplier’s mill test certificate (MTC) or material certificate.

2.1 The AA Four-Digit System for Wrought Alloys

The AA system is the common international language. Wrought alloy designations are always four digits: the first digit identifies the principal alloying element series, and the remaining three digits are merely a sequential identifier carrying no compositional information.

Table 1. Characteristics of the eight AA alloy series

2.2 The Chinese GB System: Legacy and Current Designations

Current designations under GB/T 3190 have moved fully to the “four digits plus element symbol” form, aligning with the AA system. Nevertheless, a great many drawings, molds, and legacy material lists still use the old letter codes beginning with L: LF for rustproof aluminum (Al-Mg and Al-Mn), LY for duralumin (Al-Cu), LC for super-duralumin (Al-Zn), LD for forging aluminum (Al-Mg-Si), and L for pure aluminum.

Table 2. Chinese GB designations cross-referenced to international systems

Note: 2A12 and 2024 are chemically equivalent but not fully interchangeable; impurity control limits differ slightly, so substitution in aerospace hardware requires a formal material review. Likewise, 7A04 and 7075 both belong to the Al-Zn-Mg-Cu family but differ in their zinc-to-magnesium ratio, making them similar rather than identical.

2.3 Japanese JIS and European EN

The JIS convention is the simplest of all: prefix the AA number with the letter A and append the temper separately, as in A6061-T6, A7075-T651, or A5052-H32. Note that JIS casting alloy designations form a separate system (ADC10, ADC12, AC4C, and so on) and are not interchangeable with wrought alloy designations.

The EN system is written as EN AW-four digits, where AW denotes wrought aluminum. What distinguishes EN is that the temper designation is formally part of the designation itself, for example EN AW-6061-T6 or EN AW-5083-H111. EN also defines the 6xxx-specific T66 temper, which denotes a higher level of mechanical properties than T6 achieved through special process control.

2.4 Casting Alloy Designations

Casting alloy numbering follows a completely different logic from wrought alloys and must be memorized separately. China’s GB uses the ZL prefix (ZL101, ZL104, ZL201, ZL302); the AA system uses three digits with an optional decimal suffix (A356, A380, A413, 206); Japanese JIS uses ADC or AC prefixes (ADC12, AC4C); and European EN uses the EN AC- prefix. Casting alloys fall into five principal families:

Table 3. The five casting alloy families, characteristics, and applications

A temper designation follows the alloy number, separated by a hyphen, as in 6061-T6. It directly determines the final mechanical properties of the material: the same 6061 in the O temper and in the T6 temper can differ in tensile strength by more than a factor of three. This is where procurement errors most commonly occur.

3.1 The Five Basic Tempers

Table 4. The five basic temper designations

3.2 T Temper Subdivisions: What the First Digit Means

The first digit after T (0 through 10) denotes the specific thermal treatment sequence. This is the most easily confused part of the system.

Table 5. T temper subdivisions and their process sequences

3.3 Suffix Digits: Stress-Relief Indicators

The additional two digits after the T temper indicate the method used to relieve internal stress, which is critically important for thick plate and precision machined parts.

Table 6. Stress-relief suffix designations

3.4 H Temper Subdivisions: Strain-Hardening Indicators

The H temper format is HXY, where the first digit X denotes the method of working and the second digit Y denotes the degree of hardening.

Table 7. H temper subdivisions: working method and degree of hardening

Typical examples: 5052-H32 (strain hardened and stabilized, half hard, used for marine sheet and automotive body panels) and 1100-H14 (strain hardened only, used for signage and decorative sheet).

4.1 Core Mechanical Properties of Common Grades

The table below consolidates minimum guaranteed values for extruded products, predominantly in the T6 temper, for convenient use in grade selection and finite element input.

Table 8. Minimum guaranteed mechanical properties of common grades

Data note: the values above are minimum guaranteed values from the respective standards; production material is usually stronger. Elastic modulus varies little between grades (69–72 GPa), which means switching grades is an ineffective way to increase stiffness; switching grades mainly increases strength. This point is the most frequently misunderstood in design work.

4.2 Cross-Comparison of Six Key Properties

Beyond strength, corrosion resistance, weldability, and cost often drive the selection decision. The table below grades each alloy relatively, using 6061-T6 as the reference.

Table 9. Relative performance ratings across six key properties

One rule is worth committing to memory: strength is broadly inversely related to corrosion resistance and weldability. High-strength alloys in the 2xxx and 7xxx families depend on substantial additions of Cu and Zn, and these same elements increase electrochemical corrosion tendency while reducing weldability. No material is simultaneously the strongest and the easiest to weld.

4.3 Quench Sensitivity: 7075 versus 7050

In thick-section aerospace selection, choosing between 7075 and 7050 is the most technically demanding judgment in this document. Both belong to the Al-Zn-Mg-Cu family, and 7075 in the T6 temper actually has higher tensile strength—but the two differ markedly in quench sensitivity.

7075 uses chromium as a grain-refining dispersoid. When a thick section is quenched, the cooling rate at the center is insufficient, coarse phases precipitate prematurely, and core properties degrade substantially. 7050 replaces chromium with zirconium (0.08–0.15%), which greatly reduces quench sensitivity.

Estimating on a 150 mm section: 7075-T73 loses roughly 18% of its core yield strength, down to about 357 MPa, whereas 7050-T7451 loses only about 5% and still reaches 446 MPa at the core—a roughly 25% difference in core properties between the two.

More critically, incomplete quenching at the core of 7075 not only reduces strength but simultaneously raises stress-corrosion susceptibility in that region. The conclusion is therefore unambiguous: when section thickness exceeds approximately 75–100 mm, specify 7050 rather than 7075. 7075 remains appropriate for thin sheet, thin-wall high-stress components, and cost-sensitive general high-strength structures.

5.1 Architecture, Windows, and Curtain Walls

6063-T5 or T6 dominates this application. Its advantages are the best extrudability of any grade, excellent surface finish, the finest anodizing and coloring response, and low cost. At 205 MPa tensile strength, 6063-T6 comfortably carries curtain-wall wind loads, but it must not be used for heavily loaded primary structure. For long spans or high wind pressures, move up to 6061-T6 or 6082-T6.

5.2 Aerospace Structures

Table 10. Material selection by aerospace structural location

5.3 New-Energy Vehicles and Battery Systems

Battery trays and energy-storage cabinet frames are predominantly 6061-T6, balancing strength, weldability, and heat dissipation. Where larger cross-sections demand higher strength, 6082-T6 is used. Liquid-cooling plates and thermal modules typically use 3003 or 6063 for their thermal conductivity and brazeability.

5.4 Consumer Electronics and Consumer Goods

Phone mid-frames and laptop enclosures are mainly 6xxx grades (6063, 6061) chosen for anodized appearance and formability, with 7xxx grades used in premium models to thin the chassis. Heat sinks commonly use 1050 or 6063 for thermal conductivity. Die-cast housings where thermal demand is high or cost is sensitive use ADC12.

5.5 Marine and Offshore Engineering

5083-H116 or H321 is the overwhelming workhorse, followed by 5052. The reason is that its seawater corrosion resistance is the best of any aluminum alloy, combined with good weldability that does not degrade corrosion resistance in the weld. Marine environments must avoid the 2xxx and 7xxx families unless full coating systems or sacrificial anode protection are applied.

5.6 Molds, Tooling, and Fixtures

7075-T6 or T651 is the mainstream choice for its high hardness and wear resistance. Large thick mold plates tend to favor 7050-T7451 to ensure that the plate does not distort after machining.

6.1 Fast Positioning by Performance Priority

Table 11. Grade recommendation by primary performance requirement

6.2 A Recommended Selection Sequence

1. Fix the process first, then the grade. If the part is die cast, the candidate set collapses to the Al-Si-Cu family and 6061 is simply not available. The process defines the candidate set; the grade is chosen from within it.

2. Fix the temper before comparing grades. Property differences between tempers of the same grade are often larger than differences between grades in the same temper. The gap between 6061-O and 6061-T6 far exceeds the gap between 6061-T6 and 6082-T6.

3. Identify the weakest link. If the structure must be welded, weldability is a hard constraint and the 7xxx family is eliminated immediately. If the service environment is corrosive, corrosion resistance is a hard constraint and the 2xxx family and unprotected 7xxx are eliminated.

4. Account for the thickness effect. Thick sections require checking hardenability and core properties; surface test-coupon data alone is not sufficient.

5. Specify the standard and temper completely. Purchase orders should state all four elements—grade, full temper, product form, and governing standard—for example “6061-T651 plate, ASTM B209.” Writing only “6061 aluminum plate” is an inadequate specification.

6.3 Common Misconceptions

Misconception 1: treating T6 and T651 as equivalent

Strength is similar, but T651 includes stretcher stress relief, and the difference in distortion after machining is pronounced. Using T6 for precision parts can produce post-machining warpage.

Misconception 2: performing large-radius bending in the T6 temper

T6 has lower ductility than T4 or O, and tight-radius bends are prone to cracking. The correct practice is to form in T4 or O and then age to T6 afterward.

Misconception 3: expecting a grade change to improve stiffness

Elastic modulus across grades spans only 69–72 GPa; switching to 7075 improves stiffness by less than 3%. Stiffness should be increased by adding section or changing the structural configuration, not by changing material.

Misconception 4: assuming temper does not affect corrosion resistance

For some alloy-temper combinations, stress-corrosion and exfoliation-corrosion performance differ enormously; 7075-T6 and 7075-T73 are not in the same class for stress-corrosion resistance.

Misconception 5: applying mechanical data across thicknesses

Guaranteed properties for a given grade vary with product form, thickness, and test direction. Thick-plate data cannot be applied directly to thin sheet.

Misconception 6: confirming temper by hardness alone

Different alloy and process combinations can produce overlapping hardness values. Hardness serves only as a supplementary check and does not replace the mill test certificate and tensile testing.

The core of aluminum alloy selection can be compressed into three statements: first establish whether the alloy is heat-treatable, which sets the strength ceiling; then examine weldability and corrosion resistance, the two hard constraints that define the candidate set; finally examine thickness and temper detail, which determine actual performance.

The grade is only the starting point; the temper is the destination. A complete material specification should state grade, temper, product form, and governing standard—omitting any one of the four can cause delivered material to diverge from design intent. In cross-border procurement, a cross-reference table should also be attached to prevent misreading between Chinese GB legacy codes, Japanese JIS designations, and US AA numbers.

A. Four-System Cross-Reference for Common Grades

Table 12. Cross-reference of common grades across four designation systems

B. Casting Alloy Quick Reference

Table 13. Casting alloy designations by application

C. Temper Designation Quick Reference

Table 14. Temper designation quick reference