this invention relates to a method of bonding together a plurality of ferrous metal members , the resulting assembly and a heat exchanger comprising the thusly bonded metal members in which the members are bonded to each other by assembling them with aluminum metal between and in contact with them , coating this assembly with a liquid bonding composition as disclosed in simpelaar u . s . pat . no . 3 , 301 , 688 comprising a liquid solvent and a zinc halide and heating this assembly thereby causing the aluminum to displace zinc from the zinc halide with the zinc thereby uniting with the ferrous metal to form a secure joint comprising an alloy of iron from the ferrous metal members and zinc displaced from the zinc chloride .