7129-O
Fully annealed. Used when a bumper face bar or trim must be formed heavily, for example roll-formed sweep or deep end returns. The part is then solution heat-treated and aged to reach full strength.
Bumper and bright-trim alloy
7129 T4 / T6 / O Automotive Aluminium Profile
7129 is an aluminium-zinc-magnesium-copper extrusion alloy developed for automotive bumpers. It offers strength close to 7021, with a small copper addition that gives a surface suited to plating, painting and clear-coating. Metline supplies 7129 profiles in T6, T4 and O to drawing for bumper beams, reinforcements and bright-finished parts, worldwide.
- Alloy
- 7129 (Al-Zn-Mg-Cu)
- Tempers
- T6, T4, O
- Typical yield (T6)
- about 390 MPa
- Typical use
- Bumper beams, trim
What is 7129 aluminium?
7129 is a registered Aluminum Association alloy with about 4.7 % zinc, 1.6 % magnesium and 0.7 % copper. It was developed alongside 7029 as a bumper alloy: strong enough for impact beams, and with a surface that takes chrome plating, paint or clear coat well. Of the pair, 7129 is the one normally chosen where a decorative or bright finish is needed.
The copper addition sets 7129 apart from copper-free crash alloys such as 7003 and 7021. Copper raises strength and improves resistance to stress corrosion in the peak-aged condition, but it also makes the alloy harder to weld and slightly less resistant to general corrosion. 7129 is therefore usually joined mechanically and protected by its finish.
Some older product listings describe 7129 with 1.2 – 1.5 % manganese, 2 – 3 % magnesium and no zinc. Those figures describe a different family of alloy entirely. A genuine 7129 certificate will show zinc as the main alloying element, as in the table below.
7129 chemical composition (wt %)
Registered composition limits. Each lot is certified with its actual analysis.
| Element | Minimum | Maximum | Role |
|---|---|---|---|
| Zinc (Zn) | 4.2 | 5.2 | Main strengthening element |
| Magnesium (Mg) | 1.3 | 2.0 | Strengthening with Zn |
| Copper (Cu) | 0.50 | 0.90 | Strength, SCC resistance, finishing response |
| Iron (Fe) | — | 0.30 | Kept low for surface quality |
| Silicon (Si) | — | 0.15 | Kept low for surface quality |
| Manganese (Mn) | — | 0.10 | |
| Chromium (Cr) | — | 0.10 | |
| Titanium (Ti) | — | 0.05 | |
| Vanadium (V) | — | 0.05 | |
| Gallium (Ga) | — | 0.03 | Controlled for finishing quality |
| Others, total | — | 0.15 | |
| Aluminium (Al) | Remainder |
Low iron and silicon limits reflect the alloy's purpose: fewer intermetallic particles mean a cleaner surface after polishing and plating.
Mechanical properties of 7129 by temper
Values below are typical. Guaranteed minimums depend on the specification agreed with the vehicle maker and are shown on the certificate.
| Temper | Tensile strength | Yield strength (0.2 %) | Elongation | Use |
|---|---|---|---|---|
| O (annealed) | low | low | high | Severe forming before heat treatment |
| T4 (naturally aged) | intermediate | intermediate | good | Bending and forming, then ageing |
| T6, typical | about 430 MPa | about 390 MPa | about 9 % | Finished beams and parts |
Physical properties (typical)
- Density
- about 2.80 g/cm³
- Modulus of elasticity
- about 69 GPa
- Shear strength (T6)
- about 250 MPa
- Thermal conductivity
- about 150 W/m·K
- Coefficient of thermal expansion
- about 24 µm/m·°C
- Melting range
- about 510 – 630 °C
Choosing between O, T4 and T6
7129-T4
Solution heat-treated and naturally aged. Bends and stretch-forms more easily than T6 and is aged to T6 after forming. Room-temperature hardening continues for some weeks, so form within the agreed window.
7129-T6
Peak-aged for maximum strength. Supplied straight for beams that need only cutting, punching and machining, and as the final condition of formed parts.
7129 standards and supply range
7129 is registered with the Aluminum Association and normally ordered to ASTM B221 or to an OEM material specification. It is not listed in EN 573-3; European projects with similar needs often use 7021 or 7003 instead.
| Shape | Typical outer size | Wall thickness |
|---|---|---|
| Square tube | 20 × 20 to 150 × 150 mm | 1 – 10 mm |
| Round tube | OD 6 – 300 mm | 0.5 – 20 mm |
| Rectangular tube | 10 × 20 to 200 × 400 mm | 0.5 – 10 mm |
| T and U profiles | To drawing | 1 – 20 mm |
| Multi-cell bumper sections | To drawing | To drawing |
7129 T6 profile supply range
- Section types
- Open profiles (angle, channel, T, hat), single- and multi-cell hollows, round, square and rectangular tube, solid bar
- Circumscribing circle
- Typically up to about 250 – 300 mm for 7xxx; larger sections reviewed case by case
- Wall thickness
- From about 1.5 – 2 mm for hollows, depending on section complexity
- Length
- Mill lengths of 3 – 7 m, or cut to exact length, bent, punched or machined on request
- Surface
- Mill finish, anodised, e-coated, powder coated or prepared for chrome or paint
- Documents
- EN 10204 3.1 certificate, dimensional report, PPAP-style records on request
Extrusion dies are made to your drawing. Send the section with critical dimensions and tolerances.
Forming, joining and finishing
Welding
Fusion welding of 7129 is possible but not recommended for structural joints: the copper content increases hot-cracking sensitivity. Use bolts, self-piercing rivets, flow-drill screws or adhesive bonding.
Stress corrosion
Like all Al-Zn-Mg alloys, 7129 can crack under sustained tensile stress in damp or salty service if the temper, residual stress and grain structure are wrong. Specify a controlled ageing practice, avoid cold forming after ageing, keep assembly stresses low, and ask for SCC test data (for example ASTM G47 alternate immersion) on critical parts.
Forming and bending
Stretch bending and rotary-draw bending are best done in the freshly quenched (W) or T4 condition, then aged to T5 or T6. Bending in the fully aged condition needs generous radii and raises residual stress.
Machining
Machines more cleanly than 6xxx alloys in the aged condition, with short chips and a good finish using sharp carbide tools and flood coolant.
Surface finishing
Accepts anodising, e-coating and powder coating. Zinc-rich alloys anodise with a slight yellow-grey tint, so check colour needs for visible parts. Coatings also add a barrier against galvanic and stress corrosion.
Joining to steel
Isolate 7129 from steel, carbon fibre and copper with sealants, coatings or insulating washers, and use coated fasteners, to avoid galvanic corrosion in wet road environments.
Bright finishing
For plated or polished parts, specify surface class and protect profiles from handling marks. Polish, then apply nickel-chrome plating, paint or clear coat to the finisher's process.
Automotive applications of 7129
- Bumper beams and face bars: the alloy's original purpose, in painted, plated or clear-coated form
- Bumper reinforcements and brackets: high strength in compact sections
- Pickup and truck bumpers: where a bright, decorative surface is part of the design
- Side-impact and door beams: as an alternative to 7003 and 7021
- Roof rails and exterior trim: structural trim that must also look good
7129 is a wrought extrusion alloy. It is not suited to engine-bay parts with sustained high temperatures, where 7xxx alloys over-age and lose strength, and it is not used for wiring or battery-box sheet.
7129 compared with 7021, 7003 and 6061
| Property | 7129-T6 | 7021-T6 | 7003-T5 | 6061-T6 |
|---|---|---|---|---|
| Typical yield strength | about 390 MPa | about 390 MPa | about 300 MPa | about 276 MPa |
| Copper content | 0.5 – 0.9 % | ≤ 0.25 % | ≤ 0.20 % | 0.15 – 0.40 % |
| Weldability | Poor – fair | Fair | Good | Good |
| Bright finishing | Very good | Fair | Fair | Good |
| Main use | Bumpers, bright trim | Crash beams | Crash beams | General structures |
How to order 7129 profiles
- SpecifyAlloy and temper (7129-T6, T4 or O), section drawing, length, finish class and quantity.
- Confirm the standardASTM B221 or your OEM specification, with any surface and SCC requirements.
- QuoteWe confirm availability, tolerances, certification and delivery terms (EXW, FOB, CIF or DAP) for your plant or port.
- Process and inspectProfiles are extruded, heat-treated, cut, inspected for dimensions and surface, and tensile-tested per lot.
- Document and shipEach lot ships with an EN 10204 3.1 mill test certificate and packing list, in seaworthy export packing by sea or air; third-party inspection on request.
References and standards
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
- ASTM B221 – Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes
- ASM International – Alloy Digest Al-278: Alcoa 7029 / 7129 automotive bumper alloys
- ASTM G47 – Determining Susceptibility to Stress-Corrosion Cracking of 2XXX and 7XXX Aluminum Alloy Products
- IATF 16949 – Quality management system requirements for automotive production and relevant service parts organisations
7129 automotive aluminium (aluminum) profiles: FAQ
What is the composition of 7129?
About 4.2 – 5.2 % zinc, 1.3 – 2.0 % magnesium and 0.5 – 0.9 % copper, with low iron and silicon. It is an Al-Zn-Mg-Cu alloy, not an Al-Mn-Mg alloy as some listings suggest.
What is the difference between 7029 and 7129?
They have similar mechanical properties. 7129 is the variant normally specified when the part will be plated, painted or clear-coated.
Can 7129 be welded?
It can be, but structural welding is not recommended because of hot-cracking risk. Mechanical fastening or bonding is preferred.
Why buy 7129 in T4 or O?
To form the part (bending, sweeping, stretch-forming) while it is soft, then heat-treat it to T6 for full strength.
Is there a European equivalent of 7129?
There is no direct EN designation. 7021 and 7003 are the usual European alternatives for crash beams.
Need 7129 bumper or trim profiles?
Send your drawing, temper and finish requirements. We will reply with feasibility, certification and a delivered price.
