Aluminum is a very finicky substance to weld in comparison to steel. Steel is very forgiving when it comes to working conditions and contaminants. Aluminum just won’t play fair if you don’t meet it on its terms. The fun part is figuring out what the terms are because there are so many different grades of aluminum. Old oxidized aluminum only compounds the situation.
The important part of that whole statement is that you have to meet aluminum on its terms. If you can do that then the welding process will go smooth and everybody will be happy. So, if you’re a customer paying me to work on your aluminum, what can you do to save me a little time? Really not much, except maybe to find a way to get it dry without introducing any contaminants. If it needs to be cleaned, don’t touch it! I have the proper tools and substances to take care of that. That trusty wire wheel you have will do more harm than good, trust me. The iron and other contaminants in it will be driven right into the fabric of the metal, rendering it almost impossible to weld.
Spend your extra energy getting that metal dry. Water and oil are major contaminants to aluminum and cause huge problems with welding. If you want to get oil and grease off of it, use acetone ONLY. Other cleaning agents leave residues that become unseen contaminants, and dealing with those surprises after welding has begun is sometimes a big upset in the process.
My objective is always to be productive during the time I get to spend with your project and solve your problems well. I appreciate help some customers want to give by preparing in advance, and fully understand that my time is a valuable part of the project. Everybody wants to save money now and then, but sometimes you can save money in the long run by just letting me take care of it for you. Aluminum is one of those situations.