Study On Pulse Laser Welding Technology Of AZ31B Magnesium Alloy / TC4 Titanium Alloy And Microstructure And Mechanical Properties Of Joints

The composite structure of magnesium alloy and titanium alloy can exert the excellent performance of the two materials at the same time,and can meet the structural strength requirements while reducing the weight of the structural parts.Therefore,it has great application value and wide application in modern industries such as aerospace,marine and automobile Development prospects.The welding technology of magnesium alloy and titanium alloy is called the key to study the composite structure of the two,and it has important research value and significance.However,the difference of thermophysical properties between magnesium alloys and titanium alloys is large,and there is almost no mutual solubility between the two metals.There is no metallurgical reaction,which makes it difficult for the traditional welding technology to achieve the connection of the two metals.In this paper,the finite element simulation software is used to simulate and calculate the temperature field and welding heat cycle curve of the magnesium alloy/titanium alloy laser welding process.The temperature field and the joint field of the magnesium alloy/titanium alloy lap joint form and butt joint form are studied respectively Thermal cycle curve.The simulation results show that the temperature field distribution on the magnesium alloy and the titanium alloy is asymmetric regardless of the lap or butt joint form,and the thermal cycle curve also shows the same result.Since the laser is directly irradiated on the magnesium alloy,the temperature on the magnesium alloy is significantly higher than that of the titanium alloy,whether it is a lap joint or a butt joint,the titanium alloy has a smaller melting amount.The two metals form a molten pool with the middle layer together.On the basis of studying the characteristics of temperature field distribution in the welding process,pulse laser welding of lap joints of dissimilar metals of magnesium alloy/titanium alloy was studied.Based on the idea of adjusting the welding heat input and improving the metallurgical bonding performance of the magnesium alloy/titanium alloy joint,by optimizing the welding process parameters and adding a copper intermediate layer between the upper and lower base metals,a lap deep weld with good weld formation is obtained Head,analyze the microstructure and mechanical properties of the joint.Research indicates:（1）Under the conditions of welding current 78A,pulse width 11ms,defocus amount-2mm,pulse frequency 7Hz,welding speed 180mm/mm,the surface forming and mechanical properties of the lap joint of magnesium alloy and titanium alloy are better.（2）Mg₂Cu intermetallic compound exists in the joint magnesium alloy weld,and the main compound on the titanium alloy side is Ti₂Cu intermetallic compound.（3）The fracture position of the joint is located near the interface of the titanium alloy and the magnesium alloy at the bottom of the molten pool.The main element at the fracture is Mg through the fracture EDS analysis,indicating that the fracture is at the magnesium alloy weld at the bottom of the molten pool,and the fracture mode is tough-brittle mixing fracture.Based on the analysis of the characteristics of the temperature field distribution in the welding process and the study of the pulse laser welding in the form of lap,the pulse laser welding of the magnesium alloy/titanium alloy dissimilar metal butt joints was analyzed.Using copper as an intermediate layer,a reliable magnesium alloy/titanium alloy welded joint was obtained by laser shifting to the magnesium alloy side,and the weld microstructure characteristics and the weld/titanium alloy interface reaction characteristics of the magnesium alloy/titanium alloy pulse laser welding were reserched.And analyzed the effect of the thickness of the intermediate layer on the joint interface structure and mechanical properties.Research indicates:（1）The pulsed laser welding of magnesium alloy and titanium alloy was successfully achieved by adding a copper intermediate layer and the laser was biased to the magnesium side.The copper intermediate layer melted under the action of laser and reacted with the base materials on both sides.The addition of Cu element improves the bonding performance of the weld interface and expands the connection area.（2）Controlling the content of Cu element in the weld and thus affect the structure of the weld by changing the thickness of the intermediate layer,the weak zone of the joint is transferred from the reaction zone near the titanium side to the weld zone of the magnesium alloy.When the thickness of the copper intermediate layer reaches 30μm,the joint strength reaches a maximum of 121 MPa.（3）As the thickness of the copper intermediate layer is further increased,the Mg2Cu compound in the magnesium alloy weld seam increases and the joint performance decreases.