Introduction
7003 is a 7000-series aluminum alloy built on zinc and magnesium, with a small zirconium addition that refines the grain structure in extrusions. It sits close to 7005 aluminum but leans toward better extrusion behavior rather than peak strength. The real question is whether its strength-to-weight ratio and moderate corrosion resistance fit a welded or extruded structural part better than a 6000-series grade such as 6061 aluminum.
What Is 7003 Aluminum?
7003 belongs to the 7xxx series, where zinc is the primary alloying element and magnesium forms the MgZn2 strengthening phase. Zirconium (about 0.10-0.20%) acts as a grain refiner, which helps hold strength in extruded sections. Typical composition: Zn 3.5-4.5%, Mg 0.8-1.2%, Zr 0.08-0.20%, balance aluminum. Density is about 2.78 g/cm3.
Typical Properties by Temper
| Temper | Ultimate Tensile (MPa) | Yield (MPa) | Elongation (%) | Note |
|---|---|---|---|---|
| T5 | ~315 | ~260 | ~10 | Extruded and artificially aged (most common) |
| T6 | ~340 | ~285 | ~9 | Solution heat treated and aged |
| T651 | ~348 | ~290 | ~9 | Stress-relieved after aging |
Values are representative typical figures; confirm against the mill test certificate for the specific lot.
7003 vs 6061, 7005, and 7075
| Alloy | Series | Key elements | Yield (MPa) | Weldability | Corrosion | Best fit |
|---|---|---|---|---|---|---|
| 6061-T6 | 6xxx | Mg, Si | ~276 | Excellent | Good | General structural, welded fabrications |
| 7003-T5 | 7xxx | Zn, Mg, Zr | ~260 | Fair (post-weld aging) | Moderate | Extruded light structures |
| 7005-T5 | 7xxx | Zn, Mg, Mn | ~290 | Excellent | Moderate-good | Welded high-strength frames |
| 7075-T6 | 7xxx | Zn, Mg, Cu | ~503 | Poor | Limited | Aerospace, peak strength |
Applications
- Automotive body structures and crash components (bumper beams, crash rails)
- Bicycle frames and sporting goods
- Rail vehicle body extrusions
- Structural profiles where weight matters more than peak strength
Welding, Machining, and Corrosion Limits
7003 welds with 5xxx fillers; strength in the heat-affected zone drops, but a post-weld artificial aging route can recover much of it. Machining is fair – harder than 6061, so use sharp tooling and good chip evacuation. Corrosion resistance is moderate: better than 7075 but below 6061. Avoid bare exposure in chloride or saltwater without coating, and watch stress-corrosion cracking in thick sections.
Go/No-Go Limits
Use this quick reference to decide whether 7003 fits your part.
Go – use 7003 when:
- Yield above ~260 MPa is needed in an extruded or welded light structure – 7003-T5 is a standard fit (automotive crash rails, bicycle frames, rail bodies).
- Moderate corrosion exposure with protective coating or indoor atmosphere is acceptable – 7003 holds up with anodizing or paint.
- Post-weld strength recovery through re-aging is acceptable – welded 7003 assemblies stay practical.
No-Go – do not use 7003 when:
- Peak aerospace strength or fatigue (above ~500 MPa yield) is required – 7075 or 7055 are the right grades.
- Aggressive marine or chloride immersion without coating is expected – 6000-series or 5083 resist better.
- Heavy cold forming after aging is planned – 7xxx tempers crack; form before heat treatment.
Conclusion
7003 delivers 7000-series strength in an extrudable, weld-friendly package, but its corrosion resistance and post-weld strength loss need managing, and stock of non-standard tempers can be tight at many mills. Linsy Aluminum stocks 7003 plate, bar, and extruded profiles and supplies custom dimensions at low minimum order quantities, with full MTC documentation and in-house processing and surface treatment. If your part sits between strength and weldability on the 7xxx curve, send the drawing for a grade-fit and temper review.
Frequently Asked Questions
Is 7003 stronger than 6061?
They are close. 7003-T5 matches 6061-T6 on tensile strength and the T6/T651 tempers of 7003 exceed it on yield. The trade-off is lower formability and weaker corrosion resistance than 6061, so 6061 stays the better choice when welding and forming dominate.
Can 7003 be welded?
Yes, with 5xxx fillers. Expect a strength drop in the heat-affected zone, partly recovered by post-weld artificial aging – which is why 7003 works for welded structural extrusions.
What tempers does 7003 come in?
T5 is the most common for extrusions, with T6 and stress-relieved T651 also available for higher strength.
How does 7003 differ from 7005?
Both are Al-Zn-Mg grades. 7005 adds manganese and is the stronger, more weldable of the two, while 7003 uses zirconium to control grain structure during extrusion.
What documents come with an order?
Linsy issues an MTC for every order. SGS chemical, mechanical, ultrasonic, and RoHS+REACH test reports are available on request at extra cost.
