Numerical Analysis And Experimental Study On Continuous Radial Forging And Extrusion Process Of ZK60 Magnesium Alloy Bar

Magnesium alloy bar possesses many excellent properties,such as low density,high specific strength,good conductivity,corrosion resistance,etc.It is widely used in transportation,3C electronic products,aerospace,medical and other fields.With the development of technology and related ancillary industries,the marketed application prospect of magnesium alloy is gradually improving,and it has become one of the development directions of new materials in the future.The dense hexagonal crystal structure of magnesium alloy and the small number of actuating slip systems lead to its poor plastic deformation ability.There are some defects such as difficulties and low efficiency in forming,and high manufacturing cost in production.Therefore,how to prepare magnesium alloy bars with high strength and toughness matching has attracted extensive attention and research of scholars and researchers.In this paper,based on the summary of the traditional magnesium alloy bar preparation process,we propose a new processing method— continuous radial forging and extrusion process(CRFE),that is,the process of radial forging is used for pre-deformation,and then formed at one time through large extrusion ratio,the combination of radial forging strain and extrusion strain can effectively refine the grain.The microstructure evolution mechanism and mechanical properties of bar are studied and analyzed by methods of finite element numerical simulation analysis and experimental research.The specific research contents are as follows:Firstly,the intrinsic constitutive equations of ZK60 cast magnesium alloy based on Arrhennius model derived from the hot compression experimental data were deduced and imported into the finite element software Deform material library.And the continuous radial forging and extrusion model of bar processing was established,the forming process of magnesium alloy bar under the coupling of multiple physical fields is numerically simulated to analyze the effect of cumulative depression rate,temperature and other parameters on the strain field and temperature field of the bar,and to clarify the distribution characteristics of deformation degree and temperature difference in the radial direction of bar after radial forging.Secondly,after the continuous radial forging and extrusion experience of ascast ZK60 magnesium alloy bar,it is found that after radial forging,the grains are refined in different degrees along the radial direction;In terms of organizational evolution,the coarse grains are swallowed and surrounded by fine grains,and the microstructure shows a "necklace" structure of fine equiaxed recrystallized(DRXed)grains around the coarse grains.In addition,the dynamic recrystallization degree of bar after radial forging is greatly different due to the radial strain gradient.The percentage of DRXed grains is as high as 88.2% in the external area and only 63.8% in the center,the average grain size also is increased by 4.96μm to 8.52μm.Compared with as cast bar,the mechanical properties have been significantly improved,and the yield strength and tensile strength of the material have been increased to 184 MPa and 342 MPa.After further extrusion,the radial gradient structure disappears,and its microstructure is completely replaced by DRXed grains.The uniformity of the structure is greatly improved,and the average grain size is refined to 2.43μm.It shows typical fiber texture,and the texture density is 6.41.The yield strength and tensile strength of the bar are 263 MPa and 398 MPa.The main reason for the improvement of strength properties is fine grain strengthening,while the second phase dispersion strengthening and texture strengthening also play an important role.