Study On Nugget Formation And Mechanical Property Of Inverter-based Resistance Spot Welded Non-thick AZ31B Magnesium Alloy

Magnesium alloys have many advantages suah as high strength-to-weight ratio,high damping capacity,easy machining,dimensional stability and excellent recycle,so that it replaced aluminum alloy application on the automotive,aerospace,electronics and other fields,have becoming ideal material which improve the structure lightweight and material recycle.But resistance spot welding of non-thick magnesium alloys lead to the nugget shift,which have a great influence on the the load-supporting capability.Studying resistance spot welding of non-thick magnesium alloy is not only useful for improving the quality of welding joint and the joint bearing capacity,but also very important to promoting the application of magnesium alloys in all areas.By regular resistance spot welding,additional process gaskets,different diameter electrode,these three methods of process medium was used to the inverter-based resistance spot welding of non-thick AZ31 B magnesium alloys(1.0 mm+0.7 mm).In order to analyze the effect of welding process on the quality of welded joints of non-thick magnesium alloys,The experiment was carried out on with the evaluation content of nugget diameter,shear force,nugget shift and surface spray.The research result shows that the optimum technological parameters of additional process gaskets was determined,which was 13.3 KA welding current,1.7 KN electrode pressure,90 ms welding time.The optimum tensile strength of the joint was 1936 N;The best parameters of the regular resistance spot welding of non-thick magnesium alloys was got,which was 22.4 KA welding current,1.7 KN electrode pressure,100 ms welding time.The maximum tensile strength of the joint was 1731 N;The best parameters of small diameter electrode(0.6 mm)on the side of sheet magnesium alloy was got,which was 14.4 KA welding current,1.7 KN electrode pressure,100 ms welding time.The maximum tensile strength of the joint was 1594 N.So the welded joint got from additional process gaskets resistance spot welding was best in the all aspect.To analyse the microstructure and microhardness of the joint nugget by ultra-depth digital microscope,SEM,XRD and micro-hardness tester.The results show that the microstructure of the joint nugget was composed of cellular-dendritic crystals and equiaxed-dendritic crystals,which is mainly composed of ?-Mg and ?-Mg17Al12 phases.The average microhardness respectively,the areas of cellular-dendritic crystals and equiaxed-dendritic crystals,was 57.84HV? 57.82 HV,which was higher than magnesium alloy base metal 55.44 HV.The average microhardness of the heat-affected zone was 53.94 HV,Slightly lower than magnesium alloy base metal.The welding joints were subjected to tensile loading,presenting two fracture modes,interfacial failure and button pullout failure.The two fracture modes were all belonging to brittle fracture.