Effect Of Temperature Field On Deformation Behavior Of Magnesium Alloy Tubular Part In Backward Extrusion Process

Magnesium alloy,as the lightest metal structure material,has far-reaching significance for the lightweight of weapon equipment.As one of the most representative structural parts in the field of national defense,military industry,transportation and other fields,the tubular parts has great significance for the study of manufacturing technology of magnesium alloy tubular parts.The magnesium alloy products formed by plastic forming can not only meet the shape and size requirements of the workpiece,but also improve its mechanical properties.In this paper,ZK61 magnesium alloy is taken as the research object,and the effect of temperature field on the forming of magnesium tubular parts is mainly studied.In addition,it uses numerical simulation to analyze the influence of initial billet temperature,die temperature and friction factor on the forming of the backward extrusion workpiece.The temperature range of the tube forming,as well as the microstructure,tensile properties and workpiece wall microhardness of the formed tube are studied through experiments.The results show that the dynamic recrystallization of the as extruded ZK61 magnesium alloy is incomplete and its grain size is not uniform.At room temperature,the yield strength is 135.41 MPa,the tensile strength is 210.01 MPa,and the elongation is 10.13%.In this paper,the unidirectional compression experiments of ZK61 magnesium alloy at different temperatures and strain rates are carried out,and the effects of deformation temperature and deformation rate on the deformation resistance of the material are systematically analyzed.According to the compressed data,the corresponding real stress-strain curves under different conditions are obtained,which provides the basic basis for the selection of reverse extrusion process and numerical simulation.In this paper,the finite element simulation software is used to carry out the numerical simulation analysis of the backward extrusion forming process,and the metal flow and the equivalent-stress distribution in the forming process are studied.In addition,it also studies the influence of the initial billet temperature and die temperature on the temperature field and the equivalent variable field distribution of the tubular parts.The results show that even if the billet and the die are not heated,and the maximum temperature in the process of backward extrusion reaches 203 ℃,the temperature field will be formed by the initial billet temperature,the die temperature,the heat exchange between the die and the billet and the deformation heat.Under different temperature conditions,the equivalent-strain is mainly concentrated in the inner wall and corner of the tubular part,and the equivalent-strain along the inner wall to the outer wall is gradually smaller at the same height of the tubular part wall,while the equivalent-strain along the tubular part wall axis increases from the top to the bottom.On the basis of the above simulation,the backward extrusion experiment of ZK61 magnesium alloy was carried out,and the influence of temperature field on the microstructure and mechanical properties of the backward extrusion tubular part was studied.When the initial die temperature is 100℃,the cracking occurs on the tubular wall of the tubular.With the initial die temperature rising to200℃ and 300℃,the surface quality of the tubular parts is good and there is no macroscopic crack.At the same die temperature,the dynamic recrystallization grain size in the microstructure tends to grow with the increase of billet temperature.The tensile strength,yield strength and elongation of the tubular wall were 306.11 MPa,183.47 MPa and 16.23% at the temperature of 200℃ and300℃.Compared with 250.03 MPa,177.79 MPa and 7.64% at room temperature,these data increased by 22.4%,3.4% and 112.4%.When the billet is at room temperature and the mold temperature is 200℃,the microstructure of the tubular wall is mainly twin crystal,and with the increase of the die temperature,new grains begin to appear near the twin crystal boundary.The tensile strength and elongation rate of the die at 300℃ were12.4% and 20.8% higher than that at200℃.The analysis shows that the increase of the initial billet and die temperature is conducive to the dynamic recrystallization,which improves the mechanical properties of the material.Microhardness test was carried out along the cylindrical workpiece wall.It is proved that the experimental results are consistent with the simulation results by the microhardness test along the tubular wall of shaped tubular parts.