Cracks after welding old cast parts

[3mancannon]

I'm still learning TIG welding and working on old car parts. Lately I've been fixing cast intake manifolds that are worn out from heat and dirt.

Here's what I'm using:
-180 amps with 350°F preheat
-3/32" tungsten
-#7 gas lens20 cfh argon
-60% AC balance, 50Hz
-Cleaned with acetone, stainless brush, and burr
-4043 filler rod

The weld looks good at first, but after it cools, I see small cracks near the edges. I think it might be from how the part cools or maybe dirt inside the metal. Has anyone had this happen with old cast stuff? What helped you fix it?

 

[fripoll1]

Yeah, that's pretty common with old cast aluminum but slower cooling helps, sometimes by burying the part in sand or wrapping it in a fire blanket. Then, make sure any dirt or oxides are completely cleaned out; even tiny bits can cause stress cracks

 

[terahera]

Cast aluminum is naturally porous, and liquids like antifreeze, oil, and carbon can seep into the metal, making it difficult to weld. You can try to burn out these impurities by heating the surface with an arc and wire brushing it a few times. After machining, you might find more pores that require re-welding. It can help to open up the pores slightly before you re-weld them.

For cylinder heads with significant corrosion, it's a good idea to not machine the entire surface at once. Leave the welded areas a little high until most of the pores are gone, then machine the surface to its final dimensions. You might not get rid of every single pore, but you can get it to an acceptable level. While this isn't easy work, it's a necessary step. It's interesting that you haven't used 4047 filler; other common fillers like 4043, 4943, and 5356 also produce good results.

 

[Alan]

Some guys I've seen prefer 4047 for older cast stuff