| In this paper, AZ31 B magnesium alloy and DP450 galvanized dual phase steel plate as the research object, AZ31 B brazing filler metal magnesium alloy welding wire, the process test of magnesium / zinc coated steel dissimilar metal welded by TIG welding brazing. Respectively use welding after shot peening, post weld heat treatment process and two ways of combining the composite process of welding joint quality was improved, and test research and comparison analysis of aluminum/steel welding joint microstructure and properties.When the welding current is 70 A, 0.2m·min-1 welding speed and wire feeding speed is 0.6 m·min-1, pulse frequency welding machine for 1Hz process parameters can be obtained both appearance and quality of welded joints is excellent. By the joint zone, brazing fusion zone and heat affected zone and base metal. In the optimal control parameters, the joint tensile shear strength reached 227.0 m·min-1, the fusion zone hardness above 47.6HV. Microstructure of welding zone is mainly ?-Mg matrix and precipitated phase of Mg32(Al, Zn) 49, the brazing area is mainly constituted by a plurality of mg Al Zn Intermetallic compounds composed. To influence the welding joint effect of heat input weld per unit length by forming effect of brazing layer. When the welding joint strength is low, the joint tensile shear test from the braze layer fracture cross-section was obvious brittle fracture characteristics; when the strength of welded joint is higher, the joint in the tensile shear test from the fracture of welding layer, and the surface is plastic fracture characteristics.The mechanical properties of the welded joint can be promoted by shot peening treatment under the optimal parameters. The jet strength is 0.10 MPa peened joints. The tensile shear strength reached 251 N·mm-1, hardness of the fusion zone increases to 49.1HV. Shot peening can refine the weld grain size and average grain size of the fusion zone of minimum energy dropped to only 25.4?m; On the other hand, the introduction of residual compressive stress, when the jet strength is 0.10 MPa can obtain the maximum residual compressive stress 74.02 MPa. The strength and ductility of the joint can be improved greatly by the interaction of the two mechanisms. The fracture position of the joints is located in the base metal, and the fracture surface is in good plastic fracture characteristics after the injection strength is 0.10 MPa.The mechanical properties of the welded joint were treated by heat treatment under the optimal parameters. After 200?of heat treatment temperature and 1h of heat treatment time, the hardness decreased slightly, the tensile shear strength increased to 238 N·mm-1, and the ductility was greatly improved. After heat treatment, the grain size of the weld is increased and uniform, and the residual tensile stress is reduced or even eliminated, the precipitation phase is reduced, but the internal phase composition of the weld remains unchanged. The joint after heat treatment the tensile fracture in the fusion zone of partial parent material position, the fracture surface showed significantly more ductile fracture characteristics.Finally, the comprehensive performance of the composite processing method and heat treatment after welding joint promotion of shot peening. By the method of dealing with the joint and the hardness than under conventional conditions of joint, lower than the separate use of shot peening treatment after welding joints; tensile shear strength after welding treatment process of joint are high, and ultimately get relatively good comprehensive mechanical properties of the welded joints. |
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