Goodday Weld Dr.
Oxy-Acet welding of aluminium is a lot of fun, as is all oxy welding. I have welded from thin body metal (Land Rover),to motor cycle engine castings to the Magnesium Alloy of VW engine crankcases. It is a must to use top quality flux and the correct filler. I find it usually is helpfull to preheat and when starting to weld, keep dipping into the weld area with the filler rod to ascertain when correct temperature has been reached. This is necessary because surface "skins", making it difficult to see when pool temperature is right. If you miss this temp. it is very easy to get your job too hot and have the whole piece collapse. No Fun. High magnesium contents can cause the piece to catch fire. If this occurs, don't panic, just throw flux onto the flame to extinguish it.
Lots of luck
Rinso NSW Australia