Effect of ceramic particles on microstructure and mechanical properties of aluminium alloy resistance spot-welded joints

• Ceramic particle-reinforced aluminum alloy joints are obtained by spot welding. • The microstructures of spot-welded joints in conventional aluminum alloy and ceramic particle-reinforced aluminum alloy are compared. • The mechanical properties of the ceramic particle-reinforced aluminum alloy spot-welded joint are investigated. • The influence mechanism of TiC and TiB 2 on the joint performance is revealed. To overcome the limitations of traditional 6061 aluminium alloy resistance spot welded joints, which include insufficient strength and high crack sensitivity, this study proposes the use of TiC-TiB 2 dual-phase nanoparticles-reinforced aluminium alloy as the welding material for resistance spot welding. By regulating the welding parameters, the effects of ceramic particles on the microstructural characteristics and mechanical properties of 6061 aluminium alloy resistance spot-welded joints were systematically investigated. Compared with ordinary aluminium alloy spot-welded joints obtained under the optimal parameter, the heat-affected zone and columnar crystal zone of reinforced aluminium alloy spot-welded joints are narrower, and the columnar crystal grains are significantly reduced. The addition of TiC-TiB 2 not only reduces the average grain size at the weld nugget from 23.2 μm to 10.2 μm (a 56.03 % reduction), significantly increases the equiaxed grain proportion, increases high-angle grain boundaries, obviously reduces residual stress, and increases the recrystallisation ratio from 17.1 % to 31.6 %; it also increases the microhardness at the weld nugget by 3.8 %, enhances the tensile shear strength by 19.8 %, increases the dimple density at the fracture surface, and changes the fracture mode from brittle to ductile. This study reveals that ceramic particles improve joint performance through various mechanisms.