Influence of Process Parameters on Microstructure and High-Low Temperature Mechanical Properties of 2195/2219 Dissimilar Alloy Welded Joints

This study investigates the mechanical performance of 2195/2219 friction stir welded joints under different process parameters and environmental temperatures, providing a theoretical basis for aerospace manufacturing. The results indicate that defect-free, closely bonded, and high-low temperature mechanically superior Friction Stir Welding joints can be achieved when 2219 aluminum alloy is positioned on the advancing side and welding parameters are controlled at 800 rpm-400 mm/min. Welding speed significantly influences the hardness of the weld zone (WZ) more than the rotational speed, leading to a notable hardness drop in the WZ region. Under the process parameters of 800 rpm-400 mm/min, the microhardness of the joint reaches a peak value of 125.84 HV, representing 69.91% of the hardness of the 2195 base material (BM) and 89.89% of the hardness of the 2219 BM. Regardless of the experimental environment, the tensile properties of the joint increase with rising welding speed, while the rotational speed has a minor impact on tensile performance. At room temperature, the tensile strength of the joint falls between high and low temperatures, with fracture occurring in the low hardness region near the 2219-Thermomechanically Affected Zone (TMAZ) and Heat-Affected Zone (HAZ), where the WZ experiences severe plastic deformation and dynamic recrystallization due to the shearing action of the stirring pin. This results in grain refinement and a transition from small angle to high angle grain boundaries, forming mainly recrystallized equiaxed grains. The 2195/2219-TMAZ region consists of a significant proportion of small angle grain boundaries, comprising deformed and substructured grains. In the 2219-HAZ region, the theta '' and theta ' phases dissolve and coarsen, precipitating coarse theta (Al2Cu) phases, making this area more prone to fracture.