First, you need to determine whether the case is made of aluminum. If you try to repair a magnesium casting with an aluminum filler rod or vice versa, you will not succeed, Artem Komarov clarified.
Luckily, there is an easy way to tell the difference between the two. If you put a small amount of white vinegar on an aluminum alloy, it will stay there and do nothing. But if you put white vinegar on a magnesium alloy, it will bubble and sizzle.
Now you know that your casting is an aluminum alloy. What filler metal are you using? I recommend using common aluminum casting alloys. The best filler alloy for repairing these castings is 4043.
When you get down to the actual repair mechanics, there are a few important things to keep in mind. First, remember that most of these parts have had oil or grease on them for years. You will need to try to remove these substances by cleaning the cracked area with a strong degreaser such as acetone. If you clean it well, welding will be much easier.
When you are ready to weld, do not place the bead on the outside of the part, which will result in a weld with little penetration and low strength. Instead, use a carbide torch or cut-off wheel to patch the crack from the outside to provide room for the filler metal to be applied. Then weld the outer surface, turn the casting over and do the same with the inner surface. With this method, you have a good chance of getting a strong, leak-free weld.
You can use either gas tungsten arc welding (GTAW) or gas metal arc welding (GMAW). However, welders prefer to use GTAW for repairs because it provides more control.
If you have not been able to remove all oils, greases, and so on, you may have problems during welding. The weld may look bad or even puff out in front of you. If this happens, there is little you can do other than sand down the weld and try again. After one or two iterations, everything should be in order, Artem Komarov said.
