Solid-state ultrasonic spot welding of SiCp/2009Al composite sheets

• Characterization of USWed similar SiC/2009Al alloy was investigated.
• USW joints satisfied the requirement of AWS standard D17.2 for spot welding.
• The WZ of the joints had a much higher hardness than that of BM.
• A distinctive band-like structure was observed at the center of the joints.

It has been challenging to join aluminum matrix composites (AMCs) using conventional fusion welding processes due to the occurrence of segregation and deleterious reactions between the reinforcement particles and liquid aluminum in the fusion zone. Development of robust welding processes to join AMCs thus holds the key in advanced lightweighting structural applications in the transportation sectors. The purpose of this study was to explore the weldability of AMCs via a solid-state welding technique – ultrasonic spot welding (USW). In this study 1.5 mm thick 17 vol.% SiCp/2009Al composite sheets in the annealing (O) and T6 conditions were subjected to USW, respectively, with the aim to demonstrate the welding feasibility of the composites. Microstructure, X-ray diffraction, microhardness and lap shear tensile tests were performed to evaluate the weld zone (WZ) characteristics in the USW joints. A characteristic band consisting of finer and denser crushed SiC particles that were uniformly embedded in the aluminum matrix was observed to occur in the WZ. The WZ of both types of joints had a much higher hardness than that of their respective base metal. The lap shear tensile fracture load increased with increasing welding energy and satisfied the requirement of AWS standard D17.2 for spot welding.