This question can also be asked as how to join aluminium with steel. Well the answer is quite tricky as both of them cannot be joined directly as it will lead to corrosion due to galvanic action. Superstructure are normally joined by a process named as explosive welding. In this process aluminium and steel are placed at a small distance from each other separated. An explosive is detonated above steeland due to the high pressure wave of the explosion it moves towards aluminium and gets bonded. There is a buffer plate between the steel and explosive to protect it from rupture. Aluminium is held in anvil to protect it from distortion during impact. The high velocity impact remove any oxide layer present in the 2 surfaces and give good bond. Bond is more of an atomic bond and hence more strong.
