[Skylineauto]

Did a search and did not find anything, maybe someone can help out. Doing a repair on a cast aluminum engine block. Im getting these gray cloud like balls forming when I try and add filler. It seams to form a skin on it that is not affected by the etching action of the arc. Also the are forming when I use higher currant. I have tried changing my flow from 10 to 40 CFH and everything in between. Tried different tungsten's, Different cups and so on. Rods been cleaned with scotch brite than acetone. I have tried setting my balance from 50% to 80% with not too much change. When ever it happens I go straight to a piece of scrap on the bench and it welds as it should. Machine is a Miller Dynasty 280 DX welding on A/C of course. I have used a carbide bur that I only use on aluminum to clean the surface. Cleaned the block best I could with a stainless brush, again only used on aluminum and then area is rinsed off with acetone. I have used the cleaning action of the arc to clean up the area before trying to weld it together. At my wits end here as to how to stop this from happening. I have come across it before but was able to grind the bad spot and re weld it with no issues. In the photos it the brown/gray blob to the right of the shinny part of the weld. Thanks for looking!

[Poland308]

There are some here who weld lots of cast. But my limited experience is that I had one casting weld great and another that did what you are describing. I talked to a work mate who does lots of this kind of work and found out I just needed to weld some grind out the nasty result and then weld some more till I had good metal to work with.

[DSM8]

It also looks like you have a lot of foreign contaminants on that piece, has it been thoroughly cleaned and de greased?
I have found the smallest amount of oil on a piece can wreak havoc on my welding.

[Skylineauto]

I thought I cleaned it enough. Ill get at it again tonight after cleaning it very well then clean it again.

[subwayrocket]

I've had pretty good luck cleaning cast alum with a restaurant cleaner. It's called "Chempro Heavy duty all purpose cleaner" It's for cleaning burnt grease in ovens. It's harsh if you inhale it and burns if you get a lot on your fingers. I wire brush the bulk dirt and oil off , wash it, then spray the cleaner on cast alum and let it sit a few mins and rinse . Then i'll lightly skim (with a carbide burr and die grinder) the whole area to about a half inch out from where i'll weld . I've had success doing what Jody does in his video's , get an "ugly" puddle started and start pushing good filler in . It's messy just like in his vids. When you initiate the arc, it will form ugly porosity and craters just like in Jody's video. I push some good filler into it ...then usually have to stop, let cool a little, die grind a little, wire brush a little and wash more good filler into the it and the surrounding area also . You can usually get from the scrap yard some old cast alum bell housing , misc cast alum parts , sledge hammer break them and then practice on it . Even with lots of cleaning, it's still been a little stinky and messy ...but good fun and practice . Good luck !
I am not a professional, but here is some cast alum I welded, then smash tested .
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https://youtu.be/-DSUUoJY59c?t=5s

[AndersK]

You'll have a hard time removing all crap out of that crack and surrounding pockets. Lot of that will come up to the surface when you heat it up.
Try and grind that crack into a V-slot and you'll remove a lot of the contaminants.

Better to grind deep and heli-coil afterwards.

[BigD]

I'm a TIG rookie but I've been getting somewhat OK with aluminum until I went to try to fix a broken part of a flood light stand - an insert in one of the legs connecting it to the main assembly, broke in half. Every time I tried hitting it with the welder, even at low amps, it gave off grey smoke and burned up. It was like doing spool gun aluminum welding with CO2 or wrong polarity.

I tried hitting it with a MAP gas torch and sure enough, it balled up and melted. I think it's because it's a tin alloy, not pure aluminum. I don't know how you can test the alloy but maybe you have something similar (not tin but some other nasty alloy)

[Skylineauto]

Thanks for the replies, appreciate the help. Going to get some oven cleaner as recommended and grind more of the crack out. Im also might grind most of the web bracing to get better torch angle. To add i did drill a hole in the back of the pocket to get some of the trapped argon out. did not seem to help.