The effect of the FSW variables on the microstructure and mechanical properties of the AZ91/CP-Ti joint

In this study the effect of rotational speed and tool angle parameters on the microstructure and mechanical properties of the AZ91/CP-Ti joint was investigated, for this reason the sheets with 4 x 26 x 100 mm dimensions were prepared and joint by FSW with different rotational speed (800, 1200 and 2500 rpm) and the tool angle (0.5, 1 and 3 degrees). After joining, the samples were cut and prepared for study of microstructural and mechanical properties. OM and SEM examination shows that the structure of AZ91/CP-Ti nugget zone includes alpha grains and the microstructure of the mix zone on the AZ91 side includes α-magnesium coaxial grains with Mg17Al12 intermetallic compounds. The results of the tensile test show that the maximum tensile strength value (160 MPa) related to the rotation speed of 2500 rpm and the tool angle of 1 degree. It was also determined that the rotation speed of 800 rpm was not suitable for joining of AZ91/CP-Ti. On the other hand, it was observed that by increasing the  tool angle the work piece, initially leads to an increases the strength from 141 MPa to 160 MPa and then decreases to 132 MPa. the results of the Vickers hardness test show that the average of the nugget zone hardness was to 173, which is higher than the hardness of AZ91 alloy (61 Vickers) and near to the hardness of CP-Ti (167 Vickers).