Identification of the influence of micro two-stage refilled friction stir spot welding with variation dwell time on dissimilar brass CuZn30-aluminum AA1100

Abstract

Welding and joining of brass CuZn30-aluminum AA1100 were obtained using micro two-stage refilled friction stir spot welding (mTS-RFSSW), which was carried out to eliminate the holes formed by the micro friction stir spot welding (mFSSW) process. The mTS-RFSSW process begins with the mFSSW welding process using tools with a pin inner diameter of 2.69 mm, pin outer diameter 1.811 mm and shoulder diameter of 4.954 mm, followed by a second stage process called mTS-RFSSW, which is a hole closing process using a tool with a pinless tool with shoulder diameter 4.954 mm. This study aimed to determine the effect of the second stage of dwell time on the mechanical properties produced in the mTS-RFSSW welding technique using brass CuZn30 and aluminum AA1100 with a thickness of 0.42 mm. In this study, the variable parameter is the second stage dwell time which varies from 3 s, 4 s, 5 s, and 6 s, respectively. An optical microscope that aims to observe the macrostructure shows that an upward hook is formed in each joining process. Based on the scanning electron micrograph, the resulting formation of different intermetallic compounds (IMC) with varying thicknesses occurs in every variation of dwell time. The high dwell time indicates discontinued IMC, which affects the tensile force. The IMC formed at the interface of brass CuZn30 and aluminum AA1100 is dominated by more than 30 % Cu. The highest hardness value is found in the stir zone because the formation of intermetallic compounds influences refined grains. The highest maximum shear force and cross tensile force was obtained 371.35 N and 54.88 N, respectively, in the dwell time of 3 s. The result of fracture properties after the lap shear test shows the presence of small dimples with microcracks that indicate brittle failure