Study On Forming Process Of Mg/steel And Mg/Ti Welding Based On Temperature Field Calculation

As the demand for resources in today's society,the application of single material was no longer enough to meet the production needs of human beings,by combining the materials with different properties,it would make full use of their advantages,make up for their own shortcoming,and expand its application scope,which has a broad application prospect in aerospace and lightweight field.In the previous studies of our research group,laser-induced TIG hybrid welding technology was adopted to the joining of immiscible heterogeneous metals such as magnesium alloy/steel as well as the dissimilar metals of magnesium alloy/titanium alloy,a well-formed welded joint was obtained by reasonably arranging hybrid heat source.However,it is difficult to obtain the temperature change rule of welding joint and interface through test methods due to the complex joint structure,small interface area and high peak temperature during welding.Then ANSYS software was employed for numerical calculation of welding process by selecting reasonable heat source model,the accuracy of simulated result was verified by experiment,and then combined weld joint microstructure,element distribution and interface phase composition,to investigate immiscible heterogeneous metals butt joints forming process under high interface reaction temperature.For the laser-induced TIG welding of magnesium alloy/steel,Gauss surface heat source model and column heat source model were selected as the combined heat source model,the coupling effect between laser and TIG,the overall offset of hybrid heat source and the formation of Fe-Ni solid solution zone during welding were considered,then numerical analysis model was established to calculate temperature field distribution during welding.The results showed that temperature gradient distribution on the steel side was greater than that on the magnesium alloy side,due to the larger thermal conductivity of magnesium alloy.The peak temperature of the joint could reach 2249?,nickel interlayer and its adjacent steel base material were instantaneously melted,and the peak temperature of magnesium alloy/steel interface could reach 2182?,which provided high temperature for the formation of AlNi strengthening phase,Fe-Ni solid solution zone and the interface layer with double-solid solution structure.The residence time above the liquidus of magnesium alloy was 0.28s,which ensured that the liquid magnesium alloy could fully wetted and spread on the steel side and magnesium alloy/steel joint in good forming.AlNi strengthening phase diffusely distributed in the magnesium alloy weld under the stirring action of pulsed laser on magnesium alloy melting pool,which increased the strength of magnesium alloy fusion zone,and the magnesium alloy/steel joint tensile strength could reach to 239 MPa.For the laser-induced TIG welding of magnesium alloy/steel,a double-Gaussian surface heat source model was selected to the numerical analysis of welding process when the laser was positive defocused and TIG was offset to the side of titanium alloy.The results showed that the peak temperature of magnesium alloy/titanium alloy joint was 2872?,the titanium alloy and nickel interlayer near the heat source was instantaneously melted,which provided the formation condition for strong-tough phase?-Ti.The peak temperature of magnesium alloy/titanium alloy interface was 1899?,which provided high temperature for the formation of AlNi phase interface layer and Ti₃Al continuous interface layer.During the solidification of magnesium alloy weld seam,the?-Mg phase was precipitated out,and when the temperature dropped to 506?,the eutectic reaction occurred and the??-Mg+Mg₂Ni?lamellar eutectic phase was generated.By shifting the TIG to titanium alloy,the evaporation loss of magnesium alloy could be reduced and its melting amount was increased at the same time,which ensured that there existed enough liquid magnesium alloy as the filling metal to make the joint formed perfectly.By shifting the TIG to titanium alloy,the titanium alloy surface temperature,the time above liquidus of magnesium alloy were increased,and the time above liquidus of titanium alloy was decreased at the same time,which ensured the fully wetting,spreading and interface metallurgy reaction of the liquid magnesium alloy on the titanium alloy surface,and guaranteed the good metallurgical bonding of magnesium alloy/titanium alloy joint,and the magnesium alloy/titanium alloy joint tensile strength could reach to 179 MPa.