another advantage of friction welding is that it allows dissimilar materials to be joined. this is particularly useful in aerospace, where it is used to join lightweight aluminum stock to high-strength steels. normally the wide difference in melting points of the two materials would make it impossible to weld using traditional techniques and would require some sort of mechanical connection. friction welding provides a full-strength bond with no additional weight. other common uses for these sorts of bi-metal joins is in the nuclear industry, where copper-steel joints are common in the reactor cooling systems; and in the transport of cryogenic fluids, where friction welding has been used to join aluminum alloys to stainless steels and high-nickel-alloy materials for cryogenic-fluid piping and containment vessels.