TWI Industrial Member Report Summary 201/1982
By S B Dunkerton
Direct friction welds between two aluminium alloys (5154A and 5083) and two stainless steels (321S12 and 304S15) are shown to have poor weld quality. The use of electroplated interlayers of zinc, chromium and silver, which act as diffusion barriers between the parent metals, has been investigated to establish a technique by which these materials may be joined with satisfactory joint quality.
Both zinc and chromium electroplates resulted in the production of brittle welds, zinc because of its incompatibility with the aluminium alloy and chromium because of its poor adherence to the stainless steel. Silver, on the other hand, gave good quality welds when the pre-weld plating thickness was 1.3, 5 or 13µm. A silver electroplate of 50µm exhibited similarly poor adherence characteristics as occurred with the chromium electroplate.
The 13µm thick silver electroplate is shown to give the best weld properties with shear energies in excess of 0.7J/mm2 for the 5154A alloy to 304 steel combination. Tensile and bend failures occurred in the aluminium alloy for the 5154A alloy to steel joints and ultimate tensile strengths of greater than 300N/mm2 were achieved for the 5083 alloy to steel welds.
A comparison of three different silver electroplates, all of 13µm thickness, yielded similar joint qualities. Cleanliness of the silver plate prior to welding is shown to be an important factor in relation to the weldability of the materials.