I'm designing an aluminum structure that would require welding at critical join locations. Therefore I'm studying the effects of aluminum welding on material strength of the joint. I would like to know if there's going to be strength reduction at the welding location and if so, how much reduction. Thank you.
The main loss of strength in aluminum welding is in the heat affected zone. The rule of thumb is about a 50% strength loss, but if varies by alloy. The real way to find out though is to perform a test with the same base metal and filler metal that you are going to use for your joints. Lowering heat input, such as with pulsed spray GMAW welding can help retain some of the HAZ strenght, so you may want to check that out. Also check out the AWS structural aluminum welding code. It gives you design criteria for weldments. (I think, its been a while since I've seen one)
Another way to get the more strength out of the joint is to solid state weld it. Typically you can get strengths up to 90% of parent material and often more. The only issue is the configuration of the components to be welded. The other nice feature of SS welding is that different materials can be joined and no filler material is required.
SCMAIT
I would go to Alcotec.com and look at the aluminum filler specs. In my application, boat docks, I took 6063-T5 aluminum tube from a yield strength of 20 ksi to about 11 ksi. I also lucked out in that the ends of my docks are on pipes so when the mass is in the center the joints take some of the load and the pipes bend a bit.
- Mike
The loss of strength is very dependent on the alloy and condition of the base metal. If you are welding a non-heat treatable alloy in the fully soft condition (not cold worked, or annealed) then there will be little if any decrease in strength. This condition is however unlikely.
Also, if you will be heat treating the entire weldment, made from heat treatable alloys, following welding, then you should have reasonable strength. This again, is an unlikely situation.
As stated earlier, if you are welding a strain hardened or heat treated alloy, you can bargain on losing up to 50% of the strength. It is for this reason that designing in aluminium is different to designing in steel. You need to design the weldment such that the welds are placed in low stress areas.
Regards
Niekie Jooste
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