Friction stir welding of SiCp/2009Al composite plate

Six milimeter thick hot-rolled SiCp/2009Al composite plates were successfully joined by friction stir welding (FSW) using an ultra-hard material tool. After FSW, the distribution of the SiC particles in the nugget zone (NZ) was more homogeneous than that in the base material (BM). Scanning electron microscopic examinations (SEM) and X-ray analysis (XRD) indicated that part of the Al2Cu was dissolved into the aluminum matrix in the NZ due to intense plastic deformation and high temperature during FSW. The undissolved Al2Cu particles remained in the NZ and coarsened during the cooling process after FSW. The ultimate tensile strength (UTS) of the as-welded joint is only 321 MPa and failed in the BM zone due to the low strength of the BM. After T4 heat treatment, the strength of the joint increased and became close to that of the BM with T4 temper, because most of the Al2Cu particles were dissolved into the matrix and re-precipitated homogeneously as the GP zones, which are the major strengthening precipitates for T4-tempered 2009Al alloy.