Originally Posted by
oleblu72
Another question I have about welding old aluminum is it possible to reweld a cracked weld without using filler rod by just using the torch itself or is this just not possible to make a decent weld?
Not really. You can, but it will usually crack right down the middle. Best is to vee out the old weld and if it is a high stress area that might not have been welded very good in the first place, or has been repaired a few times, grind out all the old weld to get down to the base metal and start over. Choose the right alloy for your application. 4043 is a little more ductile, while 5356 is slightly stronger. Those are the two most common alloys, but there a boatload of others for special applications. I think you mentioned Easy-Off as a cleaner, and while that does work pretty good to get out oils and grease, it leaves a black coating that you need to clean off. It really helps on things like cylinder heads that have been oil soaked. Acetone will also get a lot of crud off, but getting down into a deep crack is tough. As you weld the cleaning action will help to cook out some crud, too. Dial up a little extra cleaning and slow your travel speed to give it time to work. You can see it happening as you weld.
Long arc, short arc, heliarc and in-the-dark!