Backing material for Al6061 MIG

[IFRs]

I have tried using a copper block as a removable backing for welding 0.18 inch thick AL6061 using 4043 MIG but the copper block is sticking to the weld. Would carbon steel stainless steel, graphite, etc be the best choice? This is used inside a channel shape, the channels are legs towards each other in a 90 degree corner, we are welding the 45 degree mitered flanges and vertical web. Thanks!

 

[pandithan]

TRY WITH CERAMIC BACKING STRIP

 

[IFRs]

Thanks