The effect of preheating on mechanical properties of friction stir welded dissimilar joints of pure copper and AA7075 aluminum alloy sheets

In this paper, apart from introducing brand-new warm friction stir welding (WFSW) method, the effect of preheating on the mechanical properties of dissimilar friction stir welded copper/aluminum alloy sheets was investigated. Sheets of aluminum alloy 7075 and copper both with the thickness of 5 mm were used. The utilized welding tool was made of a H-13 tool steel with a threaded cone shape. Rotational speeds (ω) of 1200–1400 rpm and travel speeds (v) of 50–100 mm/min were used for better understanding of the effect of welding parameters on heat input. The sheets were kept in furnace with temperatures of 75 and 125 °C, and welding was done afterward. At last, tensile test was done to compare the mechanical properties of the welds. The tensile test results showed 100 % increase in the strength of preheated joints in comparison with the non-preheated joints which were welded at room temperature. Considering the high thermal conductivity of both copper and aluminum, the reason of increase in strength of the joints could be related to the low temperature gradient between the weld zone and base metal because the heat gets out of the stir zone with lower steep. The maximum strength occurred for the specimen with the preheating of 75 °C, rotational speed of 1300 rpm, and travel speed of 75 mm/min.