I am looking for a welder/process to weld cast aluminum. From a quick search, TIG or DC stick seem to be the way to go.
So i mostly do 2 stroke stuff, and a lot of that involves welding up cases to put on cylinders with bigger transfers. About 15 years ago i got pissed off that 'professional' welders told me this couldn't be done... and figured out how to do it myself. I'm not a pro welder by any means but i've talked to some people and beat my head against this long enough that i have a method that works for me... are there better ways to do it? i'm sure, but since nobody else responded to the question... most pros will say 'it cant be done'... this is how i do it.
1) clean clean clean clean. you need to bake the aluminum at 500 degrees for 2-3 hours to cook all the grease out. I usually get it as clean as i can in the parts washer, then use oven cleaner, then bake it, then wash it again with dawn dish soap.
2) prep the weld area. The key to welding cast, is as LITTLE penetration as possible. you want to float the pool on top of the base metal, not burn it in. The more you burn it, the more impurities you'll dislodge and poison the weld pool. If you need to get a deep weld you need to V it way out so the first layer of rod is setting on top and 'wetting out' on the casting.
3) preheat. I use a cheap good will special hot plate, i don't like having to mess with torches. The aluminum cools off pretty fast so you gotta put a lot of heat to it. you can use a temp stick,but the hot plate makes things really easy since you just run it full bore.
4) when you do actually get around to welding, remember the part about laying the weld on the base metal, you only want to get it hot enough for it to 'wet out', i usually try to get the puddle going a little off the rod, then just gently lick at the edge of the pool until it flows into the base metal. It will want to pop and spatter, which only gets worse the deeper you melt into the base metal
also... watch the back side, once the aluminum gets hot enough it will get soft and can sag, before the weld actually gets fluid enough to wet out. I've recked several engine cases by deforming them. You can get them hot and bolt them back together sometimes and pull them into shape but its not ideal. better to just not have it happen in the first place
also, the 'alumiweld' product works really well, and for a lot of things i will use that instead, its much lower risk if you are welding something delicate since you don't need to melt the base metal at all.
Here's the finished result on a cast aluminum hydraulic manifold from a 1957 ford tractor that broke in a really tricky spot. I welded this in 2018 and it's still holding pressure. You can see how wide I had to grind it out, over 1/2 inch for the 3/8 (approx) thick flange. Then just a matter of blobbing up enough molten ALU until its all filled in.