Influence of Weld Variables on Joint Strength of AZ61 Magnesium Alloy Sheet under Friction Stir Welding

Recently friction stir welding (FSW) method has been applied to lightweight industry owing to the several merits such as low joining defect and high effectiveness. In this study two-way factorial design method was used to evaluate the effect of joint conditions on its yield strength with friction stir welded AZ61 alloy. Joint variables were rotating speed and travel speed of tool, and their levels were 1,000, 1,500 and 2,000 rpm, and 100, 150 and 200 mm/min, respectively. The uniaxial tension tests were carried out for the variance analysis of yield strength, and ahardness measurements and microstructure observations were performed at welded part as well. From the outcomes, the variance analysis resulted in contributiveness of rotation speed of 86% and that of travel speed of 13% to the yield strength. Moreover, the optimal condition of yield strength was found as the rotation speed of 1,000 rpm and welding speed of 150 mm/min, and the presumed yield strength under the conditions was estimated to be a range of 168.93 ± 4.59 MPa in the 95% confidence interval. In addition, microstructure observation and hardness measurement were shown the crystal grain and hardness of the highest yield strength condition was refiner and higher than those of lowest yield strength condition.