Studies On Technology,Microstructures And Performances In Hot-Extrusion Of ME20M Alloy

In this study, rods and XC6218-1 sheets are prepared by tranditional direct extrusion to explore proper parameters of extrusion process and improve the mechanical properties of sheet and stable production. The flow strain phenomenon of deformation of ME20M magnesium alloy at high temperature was analysist by hot compression test. The effects of extrusion process on the grain size and the mechanical properties of ME20M magnesium alloy were investigated by Optical microscopy(OM) and tensile test at room temperature. Microstructure evolution were studied by OM,scanning electron microscopy (SEM), electron back-scattered diffraction(EBSD) and hot compression test to establish the dynamic recrystallization mechanism and effects of texture and unrecrystallization on mechanical properties of ME20M alloy. Relevant parameters were identified by orthogonal test to guide industrial production. The main results can be summarized as follows:The deformation activation energy is 149.9MPa, and it is difficult to uniform deformation during uniaxial compression. It's suitable for deformation when strain rate below 1s^-1 and the temperature above 653K. The temperature of billet in extrusion is high (Rod:above 613K; Sheet:above 653K) to weak work hardening and reduce fibrous structure.The deformation heat is main factor in promotion of recrystallization and grain growth. The relation between grain size(d) and Zener-Hollomon function is: d=1.283×10⁵Z^-0.33 ((ε|·) =0.592s^-1);d=1.463×10⁷Z^-0.57((ε|·) =1.166s^-1). The index is large compare to AZ61(0.023), and increase when strain rate raised. Raise in strain rate will form more deformation heat in short time to promote recrystallization and grain growth.There are two recrystallization mechanisms in extrusion of ME20M alloy: particle nucleation and sub-grain nucleation. Fine grain areas are mainly formed by particle nucleation and the orientation of grains is more random, and {0002} fiber texture is weak in these areas. Coarse grain areas are maily formed by twin and dislocation tangle, and the orientation of grains is more relied on deformation condition. Raise in deformation heat will promote growth of fine grains and weaken the texture.There are two main texture components, which are {0002}<11(2|ï¿£)0> and {11(2|ï¿£)1}<11(2|ï¿£)3>,getting from texture analysis.The anisotropy is greatly, and it's weaken by {11(2|ï¿£)1}<11(2|ï¿£)3> strongthen for low extrusion rate(2.5mm/s) and high temperature(693K).Extrusion effect of ME20M alloy is remarkable. The cross-section of fibrous tissue in the sample of ED direction is point-like, and increase in temperature can effectly decrease the adverse effects of fibrous tissue on mechanical properties by recrystallization. The cross-section of fibrous tissue in the sample of TD direction is band-like. Increase in temperature can decrease width of the band, but there is little change in the length of fibrous tissue. Defect can easily along the fibrous tissue, and there is more obvious tendency of brittle fracture.The extrusion parameters are as follows:ingots were heated from RT to 673±10K with extrusion container heated to 673K. The extrusion ratio is 45.9(const.) and the extrusion rate is 2.5mm/s.The sheets were successfully extruded with its thichness ultra tensile strength above 250MPa and elongation above 16% according to the extrusion parameters above.