Aluminum post heat treatment welding 1

[ralphstride]

I am working on a project and was told that that a tube (6063-T4) would be welded to a another tube (6063-T4) then heat treated to T6 and afterward beause of special bending process that a casting (356.0 T4)would be welded to this assembly. Will this compromise the strength of this assembly? In talking to the manufacturing group I know that this has not been considered in the design. In the shop a typical assembly is completely welded and then solution heat treated to T6. I am somewhat concerned about tis variation in the processing, but I am not fluent enough in this area to be sure. I will appreciate any help I can get on this.

BTW the cating cannot be welded prior to heat treat as the machine to bend the tube must grip that end.

 

[metengr]

Will this compromise the strength of this assembly?

. Only a design review of the minimum yield strength level needed for service will determine if the strength of the final welded assembly is compromised after welding the cast component. Why not heat treat the final welded assembly to achieve a T6 strength level for the 6063 and 356?

 

[tbuelna]

ralphstride-

I would agree with metengr. If you're concerned about mechanical material properties, T6 properties are better than T4. I'd suggest you weld and form the two 6063 tubes in the annealed condition, stress relieve/straighten/trim the 6063 tube weldment, weld the 6063 tube assy to the casting, then stress relieve/solution heat treat/age the final weldment to T6 cond.

T4 and T6 both are solution heat treat and aged conditions, the difference being T4 is natural (room temp) aging and T6 is artificial (elevated temp) aging. In order to save some processing time, it is common practice to weld 6XXX series aluminum in the T4 cond. and just age harden after welding. It sounds like this is the approach your mfg folks prefer. Personally, I prefer to stress relieve (if possible) after any significant forming operations or welding, since this will result in a more dimensionally stable assy over time. Fusion (GTAW/GMAW) welding aluminum effectively produces a passive gas quenching of the HAZ, which is not as controlled or uniform as the liquid quench used in a typical solution heat treatment. So once again, if mechanical properties in the finished weld are important you'll want to perform a proper HT after final welding.

Hope that helps.
Terry

 

[ralphstride]

Thank you both for your replies. The reason we are performing HT before forming is in the past we have crushed the tube and on other designs the end conditions are slim enough that they can be attached and run through the forming equipment. I think I will need to run a first article and take some samples to the lab.

I appreciate the input