Optimization of TIG repair welding process parameters to obtain maximum tensile strength in AZ91C magnesium alloy

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.