Effect of friction stir spot welding parameters on the microstructure and properties of joints between aluminium and copper

Abstract

The friction stir spot welding (FSSW) process of AA1050 and C10100 sheets using different process parameters was accomplished in two different configurations of Cu over Al (Cu-Al) and Al over Cu (Al-Cu). The experimental plan was designed according to response surface methodology (RSM), and the parameters were tool rotation speed, plunge depth and dwell time. Material flow, microstructure and microhardness of the optimum welded samples were examined using optical and scanning electron microscopy. The swirl mixing of materials, counter clockwise material flow and the streamlines of the plasticized metal were clearly observed at the stir zone (SZ) of the joints. For Al-Cu sheet configuration, the metals were not fully softened; therefore, plastic flow only occurred locally, which results in a small SZ. With the copper sheet on top, the size of the SZ enlarged. The Al-Cu configuration exhibited some lack of bonding at the sheet interface beneath the shoulder, and the copper ring extruded upward from the lower Cu plate into the upper Al plate with continuous intermetallic compounds (IMCs) developed at the interface. In the Cu-Al configuration, a discontinuous CuAl2 layer developed at the interface of Al and Cu material with a CuAl2 thickness of 160 μm. A CuAl2– CuAl–Al4Cu9 laminated layer was developed at the hook interface. The hardness values were high in the SZ for all the produced spot samples; this was attributed to the presence of hard and brittle IMC compounds.