Study On Microstructures And Mechanical Properties Of Resistance Spot Welded Joints Of Magnesium And Titanium Alloy Dissimilar Metals

As one of the lightest metal materials in the industry,magnesium metal has been widely used in auto parts,electronic instruments,aerospace and other fields with its excellent mechanical and chemical properties.Many countries have realized the importance of titanium metal materials,and have carried out continuous research and development on them,and they have been applied in aerospace,marine engineering and other fields.If the dissimilar metals of titanium and magnesium can be reliably connected,their respective advantages can be fully utilized,and their respective advantages can be complemented,and there is bound to be a greater achievement.However,due to the significant differences in the physical and chemical properties of magnesium and titanium and the poor mutual solubility of the two,they cannot form a continuous solid solution,so it is difficult to obtain high-quality welded joints with high joint strength.Therefore,this article chooses the resistance spot welding technology as the starting point to carry out the research work on the structure,mechanical properties and connection mechanism of the resistance spot welding joints of AZ31 magnesium/TA15 titanium dissimilar metals,providing a favorable theoretical basis and guiding direction for future generations to continue to explore.This article first studied the influence weights of welding parameters on the strength of joints by designing orthogonal experiments,inferred the best process parameters,and studied the changes in joint structure and the main defect forms.The results show that the magnesium/titanium resistance spot welded joint has the characteristics of melting-brazing,and the magnesium alloy nugget has the characteristics of associated crystals.Next,we studied the effects of welding parameters on the morphology,nugget diameter and tensile-shear load of resistance spot welded joints of magnesium/titanium dissimilar alloys,and analyzed the fracture modes of the joints.The results show that the maximum tensile-shear load of the joint reaches 4.21k N,and there is agglomeration of aluminum at the interface.In order to further reveal the connection mechanism of AZ31magnesium/TA15 titanium dissimilar metal resistance spot welding joints.This paper proposed to replace AZ31 magnesium alloy base material with AZ91 magnesium alloy with higher aluminum content,and conduct resistance spot welding experiments of AZ91magnesium alloy/TA15 titanium alloy to explore.The results show that the maximum tensile-shear load of the joint reaches 5.037k N,which is an increase of 25.3%compared with the use of AZ31 magnesium alloy.Finally,it is concluded that the transition layer of Al-Ti intermetallic compound(Ti Al₃)is formed due to the anti-metallurgical reaction at the interface,which promotes the bonding of the interface and improves the strength of the joint.In order to further improve the strength of magnesium/titanium resistance spot welding joints,we selected and used aluminum foil as the intermediate layer for magnesium/titanium resistance spot welding exploration experiments.The results show that the tensile-shear load of the joint is lower than that when no aluminum intermediate layer is added,and the maximum value is reduced to 3.36k N,which is 20.3%lower than that of AZ31 magnesium alloy.It is mainly due to the incomplete melting of the intermediate layer of the aluminum foil and Al12Mg17 intermetallic compounds at the interface.