Effect of welding current and Laves phase on the microstructures and mechanical properties of GTAW joints for ZC63 magnesium alloy

Abstract

Gas tungsten arc welding (GTAW) is used to successfully join ZC63 magnesium alloy extruded plates. The effect of welding current and Laves phase on the microstructures and mechanical properties of the welded joints were studied. It was found that when the welding heat input is low, the grains in the heat affected zone (HAZ) of the welded joints of ZC63 alloy with low recrystallization fraction will not grow significantly. This is due to the fact that the heat energy of the HAZ in the welding process is mostly consumed in the process of recrystallization nucleation and growth of new grains. Besides, compared to base metal (BM), The HAZ and fusion zone (FZ) present greater randomness of grain orientation and weaker crystallographic texture. With the increase of welding current, the mechanical properties of the welded joints decrease. The welded joints exhibit the most excellent properties when the welding current is 90 A (the UTS is 229 MPa, the YS is 100 MPa, and the EL is 12.6%). The FZ is the weakest position of the welded joints. The Laves phases are distributed in a continuous network at the grain boundaries in the FZ. Under the stress, the Laves phases are the initiation of crack, which eventually causes intergranular fracture of the welded joints.