Optimisation of welding parameters for ultrasonically assisted resistance spot welding of pure titanium Grade 2 and aluminium alloy 5754

Welded joints between titanium alloys and aluminium alloys, particularly aluminium alloy 5754 and pure titanium Grade 2, present challenges due to the significant differences in their physical properties. This study employs ultrasonic vibration during the resistance welding process to enhance weld quality and mechanical properties. An experimental design method was used to arrange and conduct welding operations, followed by regression analysis to establish the relationship between welding parameters and the mechanical properties of the welds under tensile shear load tests. The findings indicate that weld strength initially increases with welding current and time, peaking before declining. Increased electrode pressure negatively impacts weld strength, contrary to previous studies, as it expels liquid aluminium from the weld area, reducing the bonding area. Although pure titanium does not melt during welding, it undergoes phase transformation; specifically, the α phase converts to the β phase due to the welding heat input. Then, during cooling, the β phase forms blocky, spiked and needle-like α phases. The optimal welding parameters yield a welded joint that fails through nugget pull-out, with the aluminium alloy 5754 being pulled away.