Majid Aslani, Mahdi Rafiei,
Volume 7, Issue 2 (1-2022)
Abstract
In this study, in order to modify the weld structure obtained from repair welding of AZ91C magnesium alloy and improvement of tensile strength, input parameters such as current intensity and preheating temperature were optimized for this alloy. T6 heat treatment was separately done befor and after the welding to homogenize the microstructure and improvement of the mentioned properties. Using variance analysis, the accuracy of the models was checked and analyzed. Optical microscopy, scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS) and tensile tests were used to characterize the microstructure and mechanical properties of the repaired parts. The results of microstructural studies showed that the samples 2 (samples that were subjected to T6 heat treatment before and after welding) had continuous precipitates which these precipitates affected the strength due to the interruption of more slip planes and creating stronger barriers in the path of dislocations, resulting the better mechanical properties as compared with samples 1 (samples that were subjected to heat treatment only after welding). Also, by plotting response surface graphs and level diagrams, the highest tensile strength for samples 1 was observed at preheating temperatures of 493 to 513 K and current intensities of 80 to 90 A, and for samples 2 at temperatures of 513 to 553 K and current intensities of 100 to 110 A.
P. Chamani, H. Sabet, M. Ghanbari Haghighi,
Volume 9, Issue 2 (1-2024)
Abstract
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).
