Mexican cast aluminum, how to weld?

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Let me start by saying that I am not to the point of actually trying to weld something non-steel for real.  I've had my Miller TIG for a year now and have reached a bit of a confidence level with steel, but still have the practice regimen ahead of me with aluminum.  But, I'm looking at what may be my first alum. project and trying to prepare for it.I bought a tear drop, finned cast aluminum air cleaner that I plan to use on a nostalgic flathead Ford engine.  I need to re-work the spacing on the bottom where the thing mounts to the old 2 deuce carbs.  So, I am going to cut out the area around one of the mounting collars, cut off the mounting collar and save it.  Then, I will weld in a flat piece to replace the area cut out, reposition the collar where I need it and cut a new hole in the flat piece.  Yes, I know a picture would better explain this and I will try to get some later.When I initially cut the original piece out, I will save it and although it will be small, I can try to weld on it to see its characteristics.  Finally, my question, what kind of aluminum flat stock should I look for to mate with this Mexican cast aluminum?  What kind of filler rod should I try?  I'm thinking of getting some of this material to begin my practice on aluminum with.  I have some old aluminum street signs laying about.  Do you think that this flat stock would be compatible with the cast aluminum?Thanks in advance, my lurking on this forum has helped me immensely with my steel Tig'ing.  LouHobby welder with MIG, stick and gas experience.  Just got a Miller 250 TIG that I hope to use with some degree of expertise someday
Reply:The quality of the casting will probably be your biggest challenge. If it is a good casting welding it will be no issue. If it is a dirty casting you are in for a struggle. 4043 filler will work well for joining the two. You might need to up the amount of cleaning on the Sync to deal with the casting. Testing on the scrape piece of the casting is a good place to start for sure. As for the plate alloy, I am not sure it really matters but 3003 or an 1100 series alloy seem to weld the nicest.As for prep the cleaner the better!!!!!! This goes for any weld of course but it goes double for aluminum castings! Use a carbide burr to clean the area up and get to good parent material (you do not want and polished/coated aluminum near the weld area. If you need to wire brush it use only a stainless brush and brush in one direction only, not back and forth. The back and forth motion encourages silicon particles to form on the surface and this will make it difficult to weld cleanly. Hope this helps!Chris
Reply:Chris, thanks a lot.  I knew to use a stainless brush dedicated to aluminum use only, but I never heard that tip on one way brushing.  Sure makes sense!  Yeah, the reason I mentioned that this was a "Mexican" casting was not to cast aspersions, but I am worried about the consistency and quality, too.  It is interesting to me that it prominently has "Mexico" cast in it.  Maybe whoever did this has a lot of national pride and wanted to produce a quality piece.Hobby welder with MIG, stick and gas experience.  Just got a Miller 250 TIG that I hope to use with some degree of expertise someday
Reply:My dad always said "Aluminum is like cake batter, you never know what is in it."I would clean it, then before welding run the torch where the bead will be first, then clean the aluminum again. This will bring the crap to the surface before you weld.   I have seen people weld the first pass then grind it off because its full of crap.   Save some time and pass the torch over it first.4043 is what I would use.David Real world weldin.  When I grow up I want to be a tig weldor.
Reply:That's funny David....and SO true! Good tip on making a pass first then cleaning the gunk off the surface. Don't worry Lou I have seen good and bad casting from plenty of different countries. Some of the worst had to be early aftermarket Oldsmobile heads. I'm pretty sure there was more sand in them than aluminum! You would literally have to weld the area, grind it out, and repeat the process at least two or three times to get all the gunk out. Though to weld up a hole into water AND have it seal with all that crap in the aluminum. I was probably the most disappointed in an Italian R/C car engine block that ended up being almost as bad as the aftermarket Olds stuff! I thought it would be good quality stuff coming from Italy, live and learn.ChrisLast edited by ccm399; 02-08-2010 at 07:18 PM.
Reply:Thanks, gentlemen, for the advice.  Like I said, I'm a bit premature on this project as I need to run some beads on scrap to develop any kind of aluminum expertise first.  Hopefully I'll be able to post some pics later on showing success.  I figured this non-structural kind of project might be good to try first.Hobby welder with MIG, stick and gas experience.  Just got a Miller 250 TIG that I hope to use with some degree of expertise someday