Effect of Tool Tilt Angle on The Mechanical Properties of Friction Stir lap Welds of AZ31B Magnesium Alloy Sheets

Friction stir lap welding of AZ31B magnesium alloy sheets was conducted under various welding tool tilt angles (0°, 1°, 2°, 3° and 4°) keeping other variables constant. Tensile shear load carrying capacity and microhardness of the welds were obtained. Furthermore, the fracture mechanism of the weld was examined. The tilt angle significantly affected the weld cross-section zone and thus its load carrying capacity. At 0° tilt angle tunnel defect was seen. It was seen that the strongest joint created at 1° tilt angle was slightly more than three times stronger than the weakest one made at 4°. The joint strength considerably decreased with increasing tilt angle after 1° because the effective top sheet thickness on the advancing side was highly reduced because of more tool shoulder penetration. Hardness in heat-affected and weld zones decreased when the tilt angle was improved probably due to the more heat input. The fact that no breakage occurred from the weld areas during the tensile test is evidence of strong joining.