Weldability of CuZn30 Brass/DP600 Steel Couple by Friction Stir Spot Welding

This study deals with the weldability and assessment of the friction stir spot welding of dissimilar CuZn30 brass/DP600 steel couple. The effects of axial tool load and tool hold time were evaluated in the joining experiments. The tool load forces of 3.2 - 4.8 kN and the tool hold times of 8 s and 12 s were applied to brass/steel bimetal sheets. Tensile-shear test was employed to investigate the mechanical properties of the joint. Optical and scanning electron microscopies were utilized to characterize the microstructure of the joint having the better mechanical performance, as well as the microhardness test. Temperature measurements were also performed between the lapped sheet faces. The results show that the vertical tool load value has reached more significant influence than the tool hold time. Furthermore, the tensile-shear failure load has increased with increasing tool load and hold time and has reached the highest value of 4.6 kN. The EDS analyses on the fractured surface depict that the copper and zinc concentrations are similar to those of CuZn30 base metal. A peak temperature of 607 degrees C was measured in the weld centre of this joint. No significant microstructural change was observed in the steel sheet, while the fine grains with onion rings were revealed in the brass. Different hardness values were measured depending on microstructural change in the weld zone. Although the onion rings made a contribution to the microhardness, a softened stir zone (129.8 HV), with regard to the brass base metal (149.1 HV), was observed.