Study On Resistance Welding Of Mg/Al Dissimilar Alloy With Interlayer

With the rapid advancement of industrial development in recent years,the application range of lightweight alloys has become wider and wider,especially in the transportation industry,people's demand for reducing the weight of transportation tools and improving fuel efficiency is increasing.Dissimilar magnesium alloys and aluminum alloys are used more and more widely in the development of modern industrialization,and the welding problem of magnesium/aluminum alloys has become an urgent problem to be solved.In this paper,through the study of magnesium/aluminum direct resistance spot welding,it is found that the maximum tensile shear force of the direct spot welded joint is only 1.45 KN.The results of the fracture energy spectrum and phase analysis show that the fracture of the magnesium/aluminum side spot welded joint is mainly based on the standard.Cleavage fracture or cleavage fracture is dominant.Al₁₂Mg₁₇ intermetallic compounds are formed on both sides of the magnesium and aluminum fractures.This shows that the magnesium/aluminum direct resistance welded joint is fractured in the magnesium/aluminum intermetallic reaction compound layer,so only adjustment welding is required.Starting from the direction of the process parameters,it is difficult to obtain high-efficiency and high-quality welded joints that meet the actual application.Based on the above analysis,the paper added a CoCrFeMnNi high-entropy alloy intermediate layer between magnesium and aluminum to conduct resistance spot welding experiments.Through a reasonable design of orthogonal experiment schemes,the best welding process parameters for adding intermediate layer resistance spot welding were obtained.The pressure is 3.6 KN,the welding current is 12 KA,and the welding time is 22 ms.Under these process parameters,the maximum tensile shear force of the magnesium/aluminum resistance spot welding joint based on the high-entropy alloy CoCrFeMnNi intermediate layer can reach2.21 KN,which is an increase of 50%.The microhardness of the central part of the spot welded joint is 204 HV,which is 28%lower than that of the central area of the spot welded joint without the high-entropy alloy intermediate layer.This is the area of the spot welded joint after the high-entropy alloy intermediate layer is added.The result is that the amount of brittle intermetallic compounds is reduced.Through the morphology of the fracture area on the aluminum side of the spot welded joint,it can be seen that the fracture morphology shows dimples with tear-like patterns.The cleavage surface of the fracture area on the magnesium side contains dimples of different sizes,which indicates that the addition After the CoCrFeMnNi high-entropy alloy intermediate layer was added,the fracture mode of spot welded joints changed from brittle fracture of direct spot welding to ductile fracture.The fracture on the magnesium side is composed of magnesium matrix,high-entropy alloy matrix and Al₃Mg₂,and the fracture on the aluminum side is composed of Al matrix and Al₃Mg₂ phase.Because the CoCrFeMnNi high-entropy alloy intermediate layer is added,it can effectively prevent a large amount of liquid base metal from directly contacting,so a large amount of intermetallic compounds will not be generated in the spot welding nugget area,which improves the mechanical properties of the joint and obtains Welded joints with a certain strength.