In a lot of cases, I don't think it's a casting. What is done is to seam weld two pressings together to make the "Banjo" housing, and then stub axles are friction welded on the ends. Of course, you can weld onto a casting in many cases if it's done right.
Sorry - out of my league here. I do know that you can run into trouble welding with some medium carbon steels if you don't pre-heat the joint. So I suspect an expert might first ask you for a metallurgical analysis of the "pumpkin".
Preheat and postheat treatment is the key to doing what you want to do safely. the axel housing will give you a clue as to the who the mfr is and also the date of the casting was made. With this information, go the the mfr and ask him. you could try zr2.com to help out with the codes and the like (the mfr should be able to help with the welding procedure...)
Most truck axle housings that are castings are made with ductile iron, such as ASTM A536-84 Standard Specification for Ductile Iron Castings. These are weldable, though I will leave details to others that are more knowledgeable in that area.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
Alot depends on your load and strength requirements.Welding can be successful with pre and post heating to relieve any stresses in your heat affect zone. Try slow cooling for best results such as fire proof blanketing. Pre-heat 500-600 degrs. After welding run a post heat in the welded area to 1100 to 1200 degrs. then slow cool. Hope you have success!
