Effects of cryogenic treatment on microstructure and mechanical properties of AZ31 magnesium alloy welded joint

Against softening problems of welded joints of magnesium alloy,the MIG welded joints of AZ31 magnesium alloy were treated by cryogenic treatment with different cryogenic time.The mechanical properties and microstructures of the welded joints deep cryogenic treated with different time were tested and analyzed.The results show that the deep cryogenic treatment can significantly increase the strength of AZ31 magnesium alloy welded joint.The hardness,tensile strength and elongation of the welded joint deep cryogenic treated at-196 ℃ for 12 h are increased by 8.3%,15.43% and 10.16%,respectively.With prolonging the cryogenic time,the microstructure of AZ31 magnesium alloy welded joint become much finer and there are some dispersive second phases continuously precipitating in the matrix.