Cryogenic Treatment Of Az31 Magnesium Alloy Mig Welding Joint Microstructure And Properties Research

Nowdays, deep cryogenic treatment obtains certain results in the metalmaterial, which does not only improve the strength and ductility of material, butalso enhances the mechanical property and active time of component signfi-cantly. At the same time, it could improve the uniformity of material and thestability of work-piece, non-polluting, and does not destroy the workpiece. It hasbroad application prospects.Magnesium alloy can reduce the structural weight and production costs forits high specific strength and specific rigidity, so it has great applicationprospects in motorcycles automotive, aerospace and other fields. Magnesium-alloy, for some of the physical pharacteristics, requires higher heat input in thewelding, and high heat input easy generate welding deformations, residual stress,recrystallization of the welding zone, grain growth coarsening of the heataffected zone and performance degradation.Therefore, this paper uses deepcryogenic treatment process to improve the softening of the magnesium alloywelded joints, and improve the strength of the welded joints.In this paper, AZ31magnesium alloy MIG welding joints are studied inorder to study the effect of microstructure and mechanical properties of weldingjoints by deep cryogenic treatment. Studies found that the process of deepcryogenic treatment improved the vickers hardness, tensile strength, contractionof cross sectional area and extension percentage of the AZ31magnesium alloyMIG welding joints; the mechanical properties of welding joints got the bestimprovement after deep cryogenic treatment at-190℃f or12hours;comparedwith non-cryogenic treatment, tensile strength and vickers hardness of weldingjoints were increased by6.37%and46.51%at for12hours after deep cryogenictreatment. SEM results shew that the ductility of the welding joints wasimproved after deep cryogenic treatment, and the number of dimples graduallyincreased and tear ridge flattens. Metallographic tests showed α-Mggrainsbecome finer and the number of β-Mg₁₇A1₁₂which was dispersed increasedsignificantly of after cryogenic treatment, so it improved the continuity of the matrix. X-RD results shew the relative was enhanced intensity of α-Mg and thesecond phase β-Mg₁₇A1₁₂diffraction peak in the welding zone after deepcryogenic treatment, with the deep cryogenic temperature reduced and theholding time elongated.