Reserch On Dissimilar Inertia Friction Welding Of 7A04 Aluminum Alloy To AZ31 Magnesium Alloy

Magnesium alloy,known as the lightest metal structural materials,is attractive in the automotive,electronics,aerospace and other fields for its high specific strength,specific stiffness and recyclability.In the meantime,aluminum alloy is one of the most widely used light metal structure materials in industry,which has low density,high specific strength,specific stiffness,excellent electrical conductivity,thermal conductivity,corrosion resistance,good formability and nonmagnetic.In order to allow further design flexibility of hybrid structure and achieve a combination of individual properties,it is necessary to realize the dissimilar joining of magnesium alloy and aluminum alloy.However,the welding of magnesium alloy to aluminium alloy is considered to be a great challenge because of the formation of brittle intermetallic compounds,which degrades mechanical properties.In this study,the dissimilar inertia friction welding of AZ31 Mg alloy and 7A04 Al alloy was carried out.The effect of axial pressure on microstructure characteristics and mechanical properties of welded joint was analyzed.The inertia friction welding of Mg-Al with Zn alloys interlayer was studied,and the microstructure characteristics and the effect of interlayer on mechanical properties of joints was discussed.In addition,based on the truth of good weldability of Al-Steel,the inertia friction welding of Mg-steel/galvanized steel were conducted for a more effective interlayer for Mg-Al,the microstructure and mechanical properties of the joints were analyzed as well.The following conclusions can be drawn:?1?The effects of friction pressure on dissimilar inertia friction welding of Mg-Al have been investigated.IMCs,consisting of Mg₁₇Al₁₂ and Mg₂Al₃,were generated at the interface,including a large number of microcracks.With increasing friction pressure the thickness of IMCs layer decreased significantly.But the thickness of IMCs is about3⁷?m.The microhardness of Mg alloy substrates adjacent to the interface is higher than that of base material due to grain refinement,while that of Al alloy substrates declines under the welding conditions.This indicates that thermal softening occurred on Al alloy side.With increasing the friction pressure,the tensile strength of the weld increases remarkably.The maximum average tensile strength of 96 MPa was achieved under the friction pressure of 124 MPa.All the tensile specimens failed in quasi-cleavage fracture mode along the interface between IMCs layer and Al base metal.?2?The joints of Mg-Al welded with 5-mm-thick Zn alloy interlayer in Al side show an intimate interface.But the joints with Zn alloy failed at the interlayer and the tensile strength was 18.95 MPa.It can be speculated that the mechanical properties of the joints depend on the interlayer to some extent.?3?Inertia friction welded joints of Mg-steel with an intimate bonding were obtained under optimized process conditions.The non-equilibrium solid solution of Mg-Fe formed at the interface,which was activated by friction heat and enhanced by plastic deformation.The burn-off of the joints with end constraint is much less than that without end constraint.Additionally,the joint with end constraint exhibited intimate interface without impurities and fragments.The end constraint moderately contributed to the diffusion of Fe into Mg,as well as the concentration of Al at the interface.The microhardness of Mg alloy substrates adjacent to the interface is higher than that of base material due to grain refinement,while that of steel substrates is slightly lower than that of base material.With increasing the friction pressure,the tensile strength of the joints in both of the case increases remarkably.Additionally,the tensile strength of the joints with end constraint is significantly higher than that without end constraint.The maximum tensile strength of the joints without and with end constraint reached up to118 MPa and 126 MPa,respectively.All the tensile samples failed along the interface.?4?The Mg-steel joints welded with pure Zn and Zn-Ni interlayer electrodeposited onto the steel were produced,whose microstructure and mechanical properties were investigated.Duo to the poor combination between pure zinc coating and the steel substrate,almost no interlayer remained at the interface.The pure Zn interlayer played no role of the connecting bridge,and the mechanical properties of joints were poor.The tensile strength of the joint with pure Zn was 23.02 MPa.The Zn-Ni coating is combined with the steel substrate well,and the transition layer were formed near the interface during the welding process.However,the metallurgical reaction was not sufficient because of the low heat input,therefore the mechanical properties of the joints were poor as well.The tensile strength of the joint with Zn-Ni was 28.95 MPa.As for inertia friction welding,it is necessary to take the bonding strength between the coating and the substrate into consideration.