Improvement of weldability and fracture behavior of mild steel and A7075 aluminum alloy dissimilar friction stir welded joints by increasing welding speed

In this study, dissimilar friction stir welding of mild steel and A7075 aluminum alloy was conducted at a constant tool rotational speed (900 rpm) and different welding speeds of 100-400 mm/min with an interval of 100 mm/ min. A thermocouple was employed to record the thermal cycle and the maximum reached temperatures of the A7075/steel interface during the joining process. The higher the welding speed, the lower the maximum temperature recorded during the joining process. Conducting the joining process at a high welding speed also enhanced the cooling rate and, thus, effectively contributed towards eliminating the thermal residual stresses and suppressing the interfacial intermetallic compounds growth. As a result, 100% joint efficiency with a steel base metal fracture was obtained for the joints fabricated at the welding speeds of 300 and 400 mm/min.