Microstructure and resistance of AZ31 magnesium alloy FSW joint

Friction stir welding (FSW) of AZ31 magnesium alloy was carried out under the conditions of rotating speed of 1 200 r/min and welding speed of 30, 60, 80 mm/min respectively. Optical microscope, universal testing machine, scanning electron microscope and chemical workstation were used to analyze the effects of different welding speeds on the microstructure, mechanical properties and corrosion resistance of the samples. The results show that the welded joint consists of stir zone (SZ), thermo mechanical affected zone (TMAZ), heat affected zone (HAZ) and base metal zone (BM). Compared with the retreating side (RS), the boundary between TMAZ and SZ is more obvious on the advancing side (AS). When the welding speed is increased from 30 mm/min to 80 mm/min, the tensile strength and elongation of the joint first increase and then decrease. When the welding speed is 60 mm/min, the tensile strength reaches the maximum value of 190.3 MPa, which can reach 76% of the base metal (250.3 MPa). With the increase of welding speed, the corrosion resistance also shows a trend of first getting better and then decreasing. Under the conditions of rotating speed of 1 200 r/min and welding speed of 60 mm/min, the corrosion resistance is the best. At this time, the maximum self-corrosion voltage is −1.44 V, and the minimum self-corrosion current density is 4.5 × 10 ⁻⁵ A/cm².