Can you weld aluminum to steel?

Yes, it is possible to join aluminium and steel parts using recent welding processes, including friction stir welding
The physical properties, coefficient of expansion and electrochemical potential of these two materials are very different. With conventional welding techniques, it is sometimes difficult to guarantee quality aluminium/steel welds.
The FSW process, invented in 1991, makes it possible to weld aluminium to steel. Compared to a traditional screw/rivet process, FSW increases the mechanical strength and ensures a tight joint without filler metal.