Four wrought alloys appear on many aluminum part drawings: 6061, 5052, 6063 and 7075. Each one is a sound engineering choice for some parts and a poor one for others. This article compares them on the properties that decide a drawing callout: strength, machinability, formability, weldability, corrosion behavior and response to anodizing. All figures come from the producer datasheets and standards listed in the references, not from memory.
How to read an aluminum designation
The four-digit numbers come from the alloy designation system maintained by The Aluminum Association. The first digit identifies the main alloying element: 5xxx alloys are alloyed mainly with magnesium, 6xxx alloys with magnesium and silicon, and 7xxx alloys with zinc 1. The European equivalents use the same digits with an "EN AW-" prefix, for example EN AW-6063 [AlMg0.7Si] 4.
The letter and digits after the hyphen are the temper. They matter as much as the alloy number:
- O means annealed to the lowest-strength temper, usually to improve workability 1.
- H means strain-hardened. H3x tempers are strain-hardened and then stabilized by a low-temperature treatment, used for alloys that would otherwise age-soften at room temperature 1. The second digit gives the degree of strain hardening, with HX8 the hardest temper normally produced and HX4 about half the cold work of HX8 1.
- T6 means solution heat-treated and then artificially aged; T5 means cooled from an elevated-temperature shaping process (such as extrusion) and then artificially aged 1.
- TX51, as in T651, adds stress relief by stretching after solution treatment. For plate the permanent set is 1.5 to 3 percent 1. Where distortion after heavy material removal is a concern, consider specifying a stress-relieved temper such as T651.
One consequence follows directly from the series. The 5xxx alloys are not heat-treatable; they gain strength only by strain hardening. The 6xxx and 7xxx alloys are heat-treatable 1. A 5052 part cannot be brought to higher strength by heat treatment after forming, so the temper must be chosen at the material stage.
The four alloys at a glance
The table below collects figures from producer and stockist datasheets. Strength values are minimums from the applicable EN product standard and depend on product form and size, so treat them as a comparison, not a design allowable. Hardness values are typical.
| Property | 5052-H32 | 6063-T6 | 6061-T6 | 7075-T6 |
|---|---|---|---|---|
| Main alloying elements | Mg 2.2–2.8 % 2 | Mg 0.45–0.90 %, Si 0.20–0.60 % 4 | Mg 0.8–1.2 %, Si 0.4–0.8 %, Cu 0.15–0.40 % 3 | Zn 5.1–6.1 %, Mg 2.1–2.9 %, Cu 1.2–2.0 % 6 |
| Typical product form in the source | Sheet 0.2–6 mm 2 | Extrusion, wall ≤ 10 mm 4 | Drawn or extruded bar ≤ 80 mm 3 | Drawn or extruded bar ≤ 80 mm 6 |
| Tensile strength Rm (MPa) | 210–260 2 | ≥ 215 4 | ≥ 290 3 | ≥ 540 6 |
| 0.2 % proof stress Rp0.2 (MPa) | ≥ 130 2 | ≥ 170 4 | ≥ 240 3 | see datasheet 6 |
| Brinell hardness | 61 HB 2 | 75 HBW typ. 5 | 95 HBW typ. 3 | 150 HBW typ. 6 |
| Density (g/cm³) | 2.68 2 | 2.70 4 | 2.70 3 | 2.80 6 |
| Thermal conductivity (W/m·K) | 138 2 | 201 4 | 170–200 3 | 130–160 6 |
| Heat-treatable | No 1 | Yes 1 | Yes 1 | Yes 1 |
The strength ranking is clear. 7075-T6 bar has a minimum tensile strength of 540 MPa, nearly twice the 290 MPa minimum for 6061-T6 bar of the same size range 36. 6063-T6 and 5052-H32 sit well below 6061. The thermal conductivity column also matters for heat sinks and thermal plates: 6063 and 6061 conduct heat noticeably better than 5052 and 7075 2346.
6061: the general-purpose machining alloy
6061-T6 is the default alloy for many machined housings, brackets, plates and fixtures. Wieland rates machining in the aged condition as 2 on a scale where 1 is very good and 6 is insufficient 3. The Aluminum Anodizers Council describes 6061 as a high-strength structural alloy and "a favorite of machine shops, especially if the parts are to be hard anodized" 8.
6061 also welds well. Wieland rates MIG welding 1 and TIG welding 2 3. Corrosion resistance is good, rated 2 for weathering and 2/3 for seawater 3.
Its limits are formability and decorative appearance. Bending 6061 in the T6 temper is difficult and "will most likely require larger bending radii to avoid cracking on the outside of the bend" 11. For anodizing, Wieland rates protective anodizing 1 but decorative anodizing only 3 3.
Specify 6061-T6 (or T651 plate) when the part is machined from solid, needs moderate to high strength, and will be clear, black or hard anodized for function rather than for a precise cosmetic match.
5052: the sheet-metal alloy
5052 is a non-heat-treatable aluminum-magnesium alloy supplied in strain-hardened tempers such as H32 12. Aalco describes 5052-H32 as a medium-to-high-strength alloy with very good corrosion resistance to seawater and to marine and industrial atmospheres, very good weldability and good cold formability 2. Its listed applications include treadplate, containers, road signs, pressure vessels and welded tubes 2.
Formability is the main reason to choose it. In a press-brake bending guide published by The Fabricator, 5052-H32 is listed at 11 to 13 percent of the die opening, compared with 18 to 20 percent for 6061 even in the annealed O temper, and 5052 is described as "a close second in formability" to 3003 11. For sheet parts with tight inside bend radii, 5052-H32 is therefore the more forgiving choice, while the same geometry in 6061-T6 may need larger radii or a different forming route 11.
Machinability is rated only "Acceptable" 2. 5052 is therefore a sheet-metal alloy first.
For anodizing, the Aluminum Anodizers Council lists 5xxx alloys as giving clear coatings with good protection 9, but notes that 5052 "anodizes yellowish in thicker coatings" 8. If a sheet-metal enclosure needs a bright, uniform decorative finish, discuss the color expectation before the material is ordered.
Specify 5052-H32 when the part is bent, formed or welded sheet, corrosion resistance matters, and the strength of 6061-T6 is not required.
6063: the extrusion and decorative-finish alloy
6063 is primarily an extrusion alloy. Hydro's datasheet describes it as "used primarily for structures requiring good strength, good surface finish and good anodising response" 4. On Hydro's relative scale, where 5 is the top grade, 6063 scores 5 for decorative anodizing, corrosion resistance, weldability and cold forming, but 3 for machinability and 2 for tensile strength 4. The Aluminum Anodizers Council classes 6063 as a material suitable for architectural anodizing applications 9 and describes 6063 and 6463 as popular extrusion alloys with good strength and excellent anodizing characteristics 8.
Typical applications listed by Hydro include architectural and building products, door and window frames, electrical components and conduit, heat sinks, railings and furniture 4. Its thermal conductivity of 201 W/m·K 4 makes it a common heat-sink extrusion.
Specify 6063-T5 or T6 when the part is an extruded profile, or is machined from an extrusion, and the anodized appearance is important. Where the same part must also carry significant structural load, compare its strength with 6061 before deciding.
7075: the high-strength alloy
7075 is an aluminum-zinc-magnesium-copper alloy 6. In T6 and T651 it is the strongest of the four by a wide margin 6. GLEICH, a plate producer, lists mold making, mechanical engineering, toolmaking and industrial robots as applications for 7075 plate, and rates its machinability 1, "very good" 7. Wieland rates machining in the precipitation-hardened condition 2 6.
The trade-offs are significant:
- Welding. Wieland rates gas, TIG and MIG welding of 7075 as 6, insufficient 6. Treat 7075 as a material for machined parts that are bolted or pinned, not fusion-welded assemblies.
- Corrosion. Atmospheric and seawater corrosion resistance are rated 4/5 6, clearly below 6061 3. Consider a protective anodic coating or other finish for exposed parts.
- Forming. Wieland's plate datasheet rates 7075 as 6 for spinning and deep drawing 6. Do not design 7075 parts that need bending after heat treatment.
- Decorative anodizing. Both Wieland and GLEICH rate decorative anodizing of 7075 as 6 67. GLEICH rates hard anodizing 2 7, so functional hard coatings are practical. The Aluminum Anodizers Council notes that 7xxx alloys anodize gray, blue-gray or brown-black, depending on the alloy and the process 8.
Specify 7075-T6 or T651 when strength or wear resistance in a hard-anodized condition is the governing requirement, and appearance, welding and forming are not.
Anodizing response compared
Alloy choice decides much of the anodized appearance before the part reaches the anodizer. The Aluminum Anodizers Council states that "each alloy or alloy series yields a different appearance, even if treated to identical anodizing processes" 8. The European Aluminium Association's TALAT training material notes that among aluminum alloys, the 5xxx and 6xxx series produce the best decorative and protective coatings 12.
For hard anodizing, ISO 10074 groups alloys into classes with different minimum requirements. In the 2017 edition, Class 1 covers wrought alloys generally, while Class 2(b) covers 5xxx alloys with 2 percent or more magnesium (which includes 5052) and 7xxx alloys, with lower minimum microhardness and abrasion resistance requirements than Class 1 10. If a hard-anodized part has a hardness or wear requirement, the alloy and the coating specification have to be checked together.
| Alloy | Decorative (color, bright) | Protective / clear | Hard anodizing |
|---|---|---|---|
| 5052 | Possible; yellowish in thicker coatings 8 | Clear, good protection 9 | ISO 10074 Class 2(b) 10 |
| 6063 | Top grade on Hydro scale 4 | Clear, good protection; anodizing quality (A.Q.) 9 | Not rated in the cited sources |
| 6061 | Fair (Wieland 3) 3 | Very good (Wieland 1) 3 | Common choice 8 |
| 7075 | Not suitable (rated 6) 67 | Fair (Wieland 3) 6 | Good (GLEICH 2) 7; ISO 10074 Class 2(b) 10 |
What to write on the drawing
A material callout should leave the factory no room for interpretation:
- Alloy and temper together, for example "AL 6061-T651" or "AL 5052-H32". The temper follows the alloy number after a hyphen 1, and an alloy number without a temper is incomplete.
- Product form where it matters, such as plate, bar, sheet or extrusion, because minimum properties differ by form and size 2346.
- Finish and its relationship to the alloy. If appearance matters, state the color and the acceptance method on the drawing.
- Material documentation, if required, stated on the drawing or purchase order.
How PAXIS handles material selection
At PAXIS, the material and temper are taken from the customer's drawing. Drawing questions, including any concern that an alloy, temper or finish combination will not meet the stated requirement, are raised before quoting, and any change is approved by the customer in writing. Parts are manufactured in our network of vetted partner factories, supervised and inspected by our own team in China, and material reports or certificates are supplied where the drawing or purchase order requires them. To discuss a part, request a quote.
