TIG welding cast aluminum

[Gligor]

Hello everyone. I'm young TIG welder, and recently I started welding some nasty cylinder heads "eaten" by pure antifreeze fluid, or who knows what. Anyway, my biggest problem on those applications is POROSITY.
I am using:
-200 welding amps, with 400 degrees fahrenheit (200 degrees celsius) preheat.
-1/8 inch (3,2mm) Tungsten electrode (Tried 3/32 (2,4mm), but explodes very fast).
-Number 8 large gas lens cup.
-20-25 cfh (10-12 liters per minute) argon gas flow.
-65% AC Balance
-60Hz AC Frequency
-Acetone, carbide burr, stainless brushes, clean rags, for cleaning the surface from all the junk.
-4047 (AlSi12) filler rod (also tried 4043)

The weld bead looks decent, but after machining the cylinder heads, there are little pores, and I'm told that they are not exactly acceptable for this kind of repairs. I know that porosity in cast aluminum comes from Hydrogen caused by humidity, water, carbohydrates, stuck hydrogen in the castings, and that's why i'm preheating and cleaning the surface with the tig torch before i start dabbing, but i get porosity almost every single time.
Any advice? Thank you in advance. Now, some photos.

[metalman21]

Cast aluminum is porous to begin with some castings more and some less. The liquids (antifreeze, oil, carbon) gets into the metal and makes welding difficult. Sometimes putting the arc to it and puddling the surface, wire brushing a few times helps burn out the impurities. Pores after machining do happen and you end rewelding to get rid of them. Open the pores up a little before you reweld them.
On the heads I would suggest not machining all the way, leave the welded areas high until you get rid of the pores. You may not get rid of them completely but if acceptable then machine to finish. That head is pretty nasty corrosion wise. Never used 4047 filler. Used 4043, 4943 and 5356 with good results. Not easy work no easy answers.

[Chad86tsi]

I've had some luck welding nasty cast as bad as what you already have by gouging it all back out and starting over, this was on aluminum intake manifolds with serious corrosion, similar to what you have. the idea is you draw the contamination into your newly added fill material. That allows you to then remove it with a carbide rotary file once and for all. Now re-weld and the new filler will lay a lot nicer as most of the garbage was drawn in to your last weldment, there is less contamination to foul your new material. I've used mostly 4043, though I have a new fondness for 4943. No neeed to let it cool, quick successive passes with a heavy gouging between seems to work fine. Use WD40 for carbide bit lube, it burns off way better than anything else I've tried, won't add new contamination to the weld.

[Woznme]

Sand blasting is great for surface prep without adding contamination. I reckon 4047 is ideal for this application.

[Welder Dave]

Very common on cast aluminum to have grind out welds and redo them. The welding brings out the impurities which then cause problems with the weld. Some repairs need to be redone multiple times.

[RideKTM350]

I use 4009 Alcotec filler metal for aluminum castings, always have great luck with it.

http://www.alcotec.com/us/en/support...et_Casting.pdf

[metalman21]

Sand blasting is great for surface prep without adding contamination. I reckon 4047 is ideal for this application.

Not on engine parts. I never use any kind of blast media on engine parts. No matter how well you clean it abrasive particles can still be lodged in the surface and when they come loose they cause major damage to the internal bearing surfaces. I've seen people do it and seen the wiped out engines because of it.

[Woznme]

Not on engine parts. I never use any kind of blast media on engine parts. No matter how well you clean it abrasive particles can still be lodged in the surface and when they come loose they cause major damage to the internal bearing surfaces. I've seen people do it and seen the wiped out engines because of it.

That would be nasty

[Gligor]

So in that case, I'm not doing anything wrong with the parameters, am I? Rewelding and remachining are out of the question, due to the higher cost of the repair. These cylinder heads are usually from older beaten vehicles, and the people here don't really understand what TIG welding is, and they don't want to spend a lot of money for the repair. Also i'm not machining the heads, I'm only welding them. Those circumstances dictate me to get the weld right on the first run.
I was thinking to buy some old broken cylinder head as a test piece, and figure a way to get the weld right. I will also try grinding the welds with carbide burr and weld over them, but in that case I'm not really sure is that going to be worthwhile for me. Any additional advice is welcome. Thank you so far

[Rondo]

Wouldn't hurt to turn up your Hz to 120 or more. Otherwise on track. Good Luck !

[thegary]

i would grind until All the corrosion is gone. Then I would preheat the casting to about 250-300 degrees. That is hot enough to burn out oils and also make it to where you are not running high amps with the tig welder. Do not start welding until the casting stops smoking , then you know the oils are gone. You might need to take a burr to the surface again to clean it off. At high amps you are more prone to having tungsten spitting into the weld puddle, If you machine and hit one of the bits of tungsten you will damage the cutter and the head. If done this way you will not have to do rewelding of anything. If you have done a fair amount of tig welding you can tell when you are trapping contaminants in the weld and when you do you know to stop and grind it back out with a carbide burr until hitting good metal. Use a single cut carbide burr and use wax or parifin to keep your burr from clogging . When you get to where you have ground it out like you want go over it lightly with a clean burr to remove any wax on the surface. There is more than one way to skin a cat but In my experience this procedure has worked well for me. For 15 years I worked at a pattern shop that had an aluminum foundry that produced all their castings. I have lost count of how many tons of cast aluminum I have welded on but is several hundred tons for sure. We would rebuild many parts after they were in operation for years and they were very contaminated castings. The above procedure never let me down.

I would strip the valves and seals from the head before taking it for welding. It is easy to damage seals and or springs when preheating . It can be done without stripping but why take the chance .

[Gligor]

Thank you, i never wait for the head to stop smoking, but now i realize that the smoke might cause some contamination.
Now 2 things are on my mind:
-Should I weld the area with higher amps without filler, and try to burn all the contaminants and try to blow air bubbles before adding any filler? or
-Should I use minimal heat and use the cleaning action before adding any filler, and try to barely puddle before i start dabbing the filler, just to prevent elevating the impurities from the casting into the new metal?

[thegary]

Thank you, i never wait for the head to stop smoking, but now i realize that the smoke might cause some contamination.
Now 2 things are on my mind:
-Should I weld the area with higher amps without filler, and try to burn all the contaminants and try to blow air bubbles before adding any filler? or
-Should I use minimal heat and use the cleaning action before adding any filler, and try to barely puddle before i start dabbing the filler, just to prevent elevating the impurities from the casting into the new metal?

Those are not air bubbles , they are gas from contaminants. Some castings have more zinc in them than others and the zinc will boil and cause the bubbles. Every casting is different and the best way I found was to start by striking an arc on the casting where you want to weld. If you get black soot then go over it once or twice with out filler metal and do not worry about how much base metal you melt. You need to get the contaminants out below the surface too. Then go back and fill the area using filler rod and again I would not worry about melting into the base metal.
If when I strike an arc on it it seems to be pretty clean then I just start filling with rod right away. Just an FYI if you get a casting that seems contaminated no matter what , grind the area to be welded deeper than you normally would then put one pass in with filler. Stop and peen the area with a ball peen hammer or a punch and hammer. Then run a second pass over the first peened pass.

[Gligor]

Yes I know that they are not air bubbles, I just call them that way. Porosity is mainly caused by hydrogen from the casting process itself, and also from water, high humidity, oils, grease, paint, and other stuff. By the way, thank you very much for your tips, I'll definitely try them.

[thegary]

I have run into a few castings that were so poor that it was impossible to weld it. They were scraped . I have also found some castings that were so porous that they would leak water through the casting. We had many molds that were water cooled. In those cases I would mix steam boiler sealer 50/50 with water. Then cap the water jacket after filling it with the mix. Then heat the casting to about 300 degrees. The steam boiler stop leak would be forced into the casting as it was heated and built up pressure. Drain the water jacket of the mix and flush it out good then put the casting back in service. I probably did that a few hundred times over the 15 years I was there.

[Gligor]

Finally I got an old cylinder head to do test welding on it, I will use diferent methods as you suggested and I will post the results.
Also, what kind of lubricant should I use to grind hot welds on aluminum and prevent loading up the carbide burr. I can't find parafin, and I don't know what kind of wax should I use. I am using single cut carbide burs with large teeth, and it works well on cold aluminum, but loads up a lot when I grind hot welds. Can I use WD40, and will it work at all?

[M J D]

Automatic transmission fluid works well. Bar soap applied directly on the cutter also works. I imagine a candle would also work.

[albrightree]

I have some carbide burrs from Mcmaster carr made specifically for aluminum. If you don't load them to hard, they seem to be self clearing. I use them for cast aluminum rims which are usually full of junk.

HTH

[Welder Dave]

Let the weld cool some before grinding with a single cut burr.