Effect of Tool Shoulder Diameter to Plate Thickness Ratio on Mechanical Properties and Nugget Zone Characteristics During FSW of Dissimilar Mg Alloys

During friction stir welding (FSW), frictional heat is produced in the region between the tool shoulder and base materials due to the movement of the rotating tool along the line of joint. In this paper, an experimental investigation was made to understand the influence of the tool shoulder diameter (primary source of heat generation) on the microstructural characteristics and mechanical properties of dissimilar Mg alloys namely AZ80A and AZ91C. From the experimental results, it was observed that the use of FSW tool having 17.5 mm shoulder diameter (3.5 times the plate thickness) produced defect free sound joints with superior mechanical properties compared to its counterparts. Moreover, the uniformly distributed fine sized grains of nugget zone also contributed to the sound quality joints. From this investigation, it was understood that higher heat input is essential for enabling the required mixing of materials during FSW of dissimilar Mg alloys.