[dewdrop9]

so today I was welding some cast aluminum and I started with a practice piece and it welded fine and a fellow student brought in a piece of cast aluminum to fix a crack in so I thought I had it dialed in so I started to weld and I had to use the filler rod to start the bead because the arc was melting the crack even bigger so I used the filler rod to start the arc but the filler rod just wouldn't go into the crack it would move to one side and do the arc on one side and I couldn't get the bead to go onto the crack

any help would be appreciated
will post pictures later couldn't get them off my phone
thanks

[Otto Nobedder]

"Cast Aluminum" is mystery-meat.

TamJeff will tell you all about it.

The moment you see it's "cast", you should run. There's no telling what's in the alloy. Some are simply unweldable, and must be brazed or soldered. Some require extensive preheat/postheat. Some disagree with certain alloys, and will always crack on cooling.

Some, like transmission housings, are so embedded with oil in the pores of the casting that it's impossible to get them clean enough to weld.

It ain't you.

Steve S

[TamJeff]

Cast is a beast. The only way to conquer some of them is to treat them like solder joints. By that I mean "tinning" the area with weldable aluminum by way of filler a little at a time. First pass may look like ass, but then you grind the dirt away leaving at least 'some' clean metal. It may take a few attempts of the tinning and grinding. Another trick is to weld it in reverse. The gas blowing directly onto the weld puddle sometimes makes the difference. Instead of treating the repair as a weld pass, you may have to break it down puddle by puddle, or an assemblage of tacks on tacks. I typically use 5356 rod for welding cast. Multiple attempts sometimes helps to cook the offending contaminants out of it.

Sometimes, the only way to repair it, especially damage that is in a highly stressed, interior section, is to weld a bandaid coupon over it. Or weld a backer on it to give you some clean metal to weld to and just wash the molten weld bead onto the cast without actually melting it with the arc itself.

Otto is correct. Much of it is indeed oil soaked to the point where it may as well be pot metal you are trying to weld.

[nova_70_383]

i weld for a local foundry... imagine welding cast aluminum and having it pass x-ray!

[TamJeff]

Some cast welds beautifully, at least when new. There's good money welding cast. Many welders will give it one try and condemn it as "unweldable." If you manage to develop a high success rate with it, people will pay pretty much exactly what it's actually worth.

Half the world is held together with cast aluminum.

[dewdrop9]

Cast is a beast. The only way to conquer some of them is to treat them like solder joints. By that I mean "tinning" the area with weldable aluminum by way of filler a little at a time. First pass may look like ass, but then you grind the dirt away leaving at least 'some' clean metal. It may take a few attempts of the tinning and grinding. Another trick is to weld it in reverse. The gas blowing directly onto the weld puddle sometimes makes the difference. Instead of treating the repair as a weld pass, you may have to break it down puddle by puddle, or an assemblage of tacks on tacks. I typically use 5356 rod for welding cast. Multiple attempts sometimes helps to cook the offending contaminants out of it.

Sometimes, the only way to repair it, especially damage that is in a highly stressed, interior section, is to weld a bandaid coupon over it. Or weld a backer on it to give you some clean metal to weld to and just wash the molten weld bead onto the cast without actually melting it with the arc itself.

Otto is correct. Much of it is indeed oil soaked to the point where it may as well be pot metal you are trying to weld.

thanks I like the idea of welding it backwards I would of never thought of it and I don't have a foot pedal would that help things?

[TamJeff]

I use a torch mounted momentary switch. That would be minimal I think. You have to be able to control the heat somehow. I often have to feather the switch on/off as I am simultaneously adding filler so I can freeze it once it sticks, for lack of a better explanation. Sometimes you can feather in cold tacks to help subdue the crack momentarily until you are able to get more substantial tacks in place.

Bump welding is another good trick for cast in some situations. Especially if you are somewhat new to TIG/aluminum welding.

[TamJeff]

Some pros look at bump welding the same as adding cream and sugar to perfectly good coffee, but it's a very effective process with contaminated parts, or gaps, or in nearly impossible positions. It also allows you to use super high heat where needed. I can weld .125 with 250 amps bump welding, and fill half inch gaps with a single pass.