No. In almost all cases you cannot weld disimilar metals. Some metals can be brazed or soldered together. This where you use a third metal that will "bond" to both of the other metals and even in this case you are most often bonding two of the same metal to each other but you need a low temp so as not to damage anything.

Alluminum dropouts can be purchased or made and welded in by a competent weldor.