Can 7075 aluminum be welded?
Not by arc welding. 7075 hot-cracks in the weld, loses most of its strength in the heat-affected zone and becomes prone to stress corrosion. Friction stir welding is the exception; otherwise bolt, rivet or bond it.
7075 is classed as non-weldable by fusion processes, and shops that do it are repairing, not fabricating. The zinc-magnesium-copper chemistry that makes it the strongest common aluminum also puts it in the worst region for hot cracking: the weld metal tears as it solidifies, and the partially melted zone next to the fusion line cracks along grain boundaries. The heat-affected zone over-ages and loses roughly half its T6 strength, from about 570 MPa (83 ksi) tensile down toward 275-300 MPa (40-44 ksi), and it does not recover with natural aging. Worse, the as-welded microstructure is sensitive to stress-corrosion cracking, so a welded 7075 part can fail in service without any visible weld defect. AWS D1.2 does not provide allowables for it.
Fillers do not fix this. ER5356 gives the most crack-resistant fusion weld in 7075 and is what a repair shop would try, and ER4043 is sometimes used for cosmetic sealing welds, but both produce a joint far weaker than the parent metal and neither addresses the corrosion sensitivity. Post-weld solution treatment and aging to T6 or T73 recovers strength but distorts the part and is rarely practical. Resistance spot welding is possible on thin sheet with tight schedules and is used in some aerospace structure, again under strict process control.
The exception is friction stir welding (FSW). Because the metal never melts, there is no hot cracking, and the joint retains about 70-80% of T6 strength; the aerospace and automotive industries FSW 7075 in longitudinal seams on tanks, panels and extrusion assemblies. It needs a dedicated machine and a rigid backing fixture, so it suits long straight or gently curved seams in production, not one-off brackets. For everything else, design the joint mechanically: bolts and blind rivets in properly sized holes, adhesive bonding with a structural epoxy on a chromate or anodized surface, or a machined-from-solid design that removes the joint. If a design truly needs a welded aluminum frame, use 6061 or 5083 instead.
Welding for 7075 parts: where to send them
What to specify
- Do not call out arc welding on 7075; state "no welding" on the drawing so a shop does not repair a scrapped part by welding
- For mechanical joints: fastener type, hole size and fit (for example H9 or a specified clearance), and edge distance of at least 2x hole diameter
- For adhesive bonding: the adhesive, surface preparation (chromate conversion per MIL-DTL-5541 or chromic/phosphoric anodize) and the bond-line thickness
- For friction stir welding: joint type (butt or lap), the tool side, the fixture, and acceptance by macro section and tensile coupon
- Temper for stress-corrosion resistance: T73 or T7351 where the part sees sustained tension in the short-transverse direction
- If a repair weld is ever authorised, require ER5356 filler, engineering approval and a stated derating of the joint
Pitfalls
- A "small tack weld to hold it" on 7075 cracks and starts a stress-corrosion crack that grows in service
- Welded 7075 repair on a scrapped part: the part looks fine, passes a dimensional check, and fails at the weld under load
- Assuming 4043 or 5356 filler makes it weldable: it makes a weld possible, not a joint with usable strength
- Anodizing does not restore the corrosion resistance of a welded zone; the sensitivity is in the metal, not the surface
- Mixing alloys: a 6061 tab welded to a 7075 body still puts a fusion weld into the 7075
- Using 7075 for a frame that must be welded because "it is stronger"; a welded 6061-T6 joint is stronger than a welded 7075 joint
Frequently asked questions
- Why can 7075 aluminum not be welded?
- Its zinc, magnesium and copper make the weld hot-crack as it solidifies, the heat-affected zone loses about half its strength, and the as-welded metal is prone to stress-corrosion cracking. Fusion welds in 7075 are weaker and less reliable than the same joint in 6061.
- Can 7075 be TIG welded at all?
- A bead can be laid with ER5356 filler, and repair shops occasionally do it for cosmetic or non-structural purposes. It is not an engineering joint: expect cracks, a soft zone at roughly half of T6 strength, and stress-corrosion sensitivity.
- What is the alternative to welding 7075?
- Friction stir welding for long production seams; bolted or riveted joints and structural adhesive bonding for everything else; or a machined-from-solid redesign. If the assembly must be arc welded, change the alloy to 6061 or 5083.
- Can 7075 be brazed or soldered?
- Not practically. Its melting range starts near the brazing temperature and it loses its temper in the process. Adhesive bonding on a chromate-converted or anodized surface is the usual non-mechanical joining method.
