Microstructure and mechanical behavior of friction spot welded AA6181-T4/Ti6Al4V dissimilar joints

Abstract

Friction spot welding has become an excellent alternative to produce dissimilar joints in a fast and reliable way. This paper investigates the microstructure and the mechanical behavior of friction spot welded AA6181-T4/Ti6Al4V dissimilar joints produced by two different tool rotational speeds, 2500 and 3000 rpm, previously demonstrated to be the welding parameter with the most influence on the mechanical performance of these joints. Temperature profiles indicated that tool rotational speed directly affects the process temperature and, consequently, the metallurgical reaction taking place at the joint interface. Higher temperatures (3000 rpm condition) resulted in a complex and cracked Ti/Al interface because of the local melting of the aluminum plate. In contrast, by decreasing the process temperature (2500 rpm condition), a continuous thin TiAl3 layer was observed, increasing the lap shear resistance of the joints. Moreover, the local Von Mises strain distribution of a sound joint under lap shear was successfully associated with the different stages of a typical force–displacement curve and used to elucidate the fracture evolution. Lastly, the fatigue behavior of the joints indicated that FSpW dissimilar welds exhibited a better performance than FSpW aluminum similar joints.