Welding parameters analysis and microstructural evolution of dissimilar joints in Al/Bronze processed by friction stir welding and their effect on engineering tensile behavior

The effect of welding parameters on the joint properties in dissimilar friction stir welding (FSW) between AA5052 alloy and C22000 Bronze alloy was investigated in this study. The FSW process was carried out at rotational speeds of 800, 1000, 1250 and 1400 revolutions per min (rpm) and welding speeds of 20, 31.5 and 50 mm/min. Results showed that welding under 800 rpm is impossible due mainly to the lack of heat input as well as the appearance of tunnel defects. Results also showed that the increase of rotational speed causes an increase in the fraction of intermetallic layer and the appearance of ring/layer pattern in nugget zone. As well, it was found from EBSD analysis that the difference in stacking fault energy of Aluminum and Bronze leads to different dynamic recrystallization behavior in Aluminum and Bronze parts undergoing equivalent amount of thermo-mechanical process in the nugget zone. Mechanical strength showed that there is a direct relation between the amount of interface of the base metal impressed by welding parameters and the mechanical strength of the joints. Finally, it was found that the maximum amount of ultimate tensile strength (UTS) for the joint was about 64% of the UTS of the Aluminum base metal. This was achieved through changing the welding parameters such that the interface length between the base metals was the highest and in contrast the interacting intermetallic layer, which acts as a bond between the base metals, was the narrowest.