Aluminum casting modification

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I have a precesion cast aluminum piece I need to modify (or at minumium use the flange off of.  The original data I found says it's made from Aluminum alloy 308 (90% aluminum 5% copper and 5% silicon)  What filler 5056 or 4043 would be better?  and should I preheat?  flange thickness is about 1/4"  and the tube portion is about 1/16" thick.  the flange in the upper left of the pic is the one that's a bear to replicate.  I need to make that leg of the tube that goes to that flange longer.pic:
Reply:4145 would be the correct fiiller. Being its a small casting a preheat of 350 should be fine. The 5% silicon will help with crack sensitivity.
Reply:I can't tig  I can only mig weld it.  that's why I was thinking the 4043 or possibly 4047  as of right now I only have 5056 at home.
Reply:4047 would be a second choice, 4043 a last resort. You cannot use 5356 filler. Whats the application? What equipment do you have to use?
Reply:All I have is a small 110 v Nothern Mig135 welder.   The part is an intake adapter  going between a Carb and the intake manifold on an older military surplus engine I'm converting to run on propane/nat gas.   it other option might be to fab up a new elbow between the carb and air cleaner rather than trying to mount this block I've made.  there's just no room fit the block I make in the "stock" setup.I'd try to get it into work to have it welded, it's just not possible anymore.
Reply:Originally Posted by mdlbldrmatt135All I have is a small 110 v Nothern Mig135 welder.   The part is an intake adapter  going between a Carb and the intake manifold on an older military surplus engine I'm converting to run on propane/nat gas.   it other option might be to fab up a new elbow between the carb and air cleaner rather than trying to mount this block I've made.  there's just no room fit the block I make in the "stock" setup.I'd try to get it into work to have it welded, it's just not possible anymore.
Reply:if that flange for the manifold wasn't soo funky looking it wouldn't be a big deal.   it's a really tight fit where the carb is moiunted.The elbow to the right hand side is the one I'll have to make a replacement for.