Study On Mg-RE/TC4 Dissimilar Metaldiffusion Welding

Magnesium alloys have attracted the attention of researchers because of their low density,high specific strength,high specific stiffness,strong damping and noise reduction performance,excellent electromagnetic shielding performance and low manufacturing cost.They are widely used in aerospace,rail transit and 3C products.However,the poor high-temperature mechanical properties and poor corrosion resistance of magnesium alloys seriously restrict their application prospects.Titanium alloy is widely used in aerospace,petrochemical and biomedical fields because of its high specific strength and stiffness,excellent oxidation resistance,corrosion resistance,strong fracture toughness and high temperature resistance.In order to realize the lightweight process of aerospace equipment,the low-density,high-strength,good corrosion resistance and damping properties of magnesium titanium composite structural materials are brought into play in the form of magnesium/titanium dissimilar metal composite,and magnesium/titanium dissimilar metal diffusion welding can largely avoid the instability of welded joints caused by the physical and chemical properties of magnesium and titanium,Realize the effective connection of magnesium/titanium dissimilar metals.In this paper,the microstructure and properties of magnesium/titanium dissimilar metal vacuum diffusion welding joint were studied.The magnesium/titanium dissimilar metal vacuum diffusion welding experiment was carried out with Mg884(Mg-8Gd-3Y-1Zn-1Mn,wt%)rare earth magnesium alloy containing Mn and TC4titanium alloy as experimental materials.The equipment such as metallographic microscope(OM),scanning electron microscope(SEM),transmission electron microscope(TEM-EDS,STEM)and universal mechanical testing machine were used,The effects of different welding temperatures on the microstructure and mechanical properties of magnesium/titanium vacuum diffusion welding interface were studied,and the formation mechanism of diffusion welding joint was explored.On this basis,TC4/Mg884/TC4 three-layer composite plate structure was prepared by vacuum diffusion welding technology,and the mechanical properties of the composite plate were tested.The fracture form and fracture mechanism of the composite plate were analyzed by tensile experiment.The results show that the effective connection between Mg884 rare earth magnesium alloy and TC4 titanium alloy can be realized at 460?,480?and 500?.The thickness of diffusion reaction layer increases with the increase of welding temperature.At 500?,the thickness of reaction layer is about 75 nm,The TEM-EDS surface scanning results of reaction layer show that the thickness of Mn enrichment layer increases with the increase of diffusion temperature.A large number of Y containing and Gd containing precipitates are attached to Ti Mn reaction layer,thanks to a large number of Mg₂Y and Mg₂Gd phases anchored on Ti Mn phase,The other end goes deep into the magnesium alloy base metal to play the role of rivet connection,which greatly enhances the welding strength of Mg884/TC4.The tensile strength of welded joints decreases with the increase of welding temperature.When the welding temperature is 460?,the maximum tensile strength of welded joints is 320 MPa,but the tensile curve shows typical brittle fracture and the reliability coefficient of engineering application is low;The welding temperature is 480?,the tensile strength is 310 MPa,the tensile curve shows yield phenomenon,and the engineering application reliability is high.The shear strength of welded joints increases first and then decreases with the increase of welding temperature.The maximum shear strength is 150 MPa at480?.The maximum tensile strength of TC4/Mg884/TC4 diffusion welded three-layer composite plate under the welding temperature of 480?and heat preservation for 120min is 673 MPa and the density is 2.97 g/cm~3,which is only 5.7%higher than that of commercial 7075 aluminum alloy,but the tensile strength is increased by nearly 30%.At the same time,the fracture elongation of magnesium alloy in the composite plate under the action of high elastic modulus on both sides and high shear force of TC4 plate reaches 15.1%,The elongation of magnesium alloy plain plate treated by the same process is twice as high as that of magnesium alloy plain plate treated by the same process.The tensile fracture mode of the composite plate is that the intermediate magnesium alloy breaks first,and then the titanium alloy necks at the fracture position of the magnesium alloy until it breaks.