Study Of Equal Channel Angular Pressing On Microstructure And Mechanical Properties Of ZAM84-2Si Magnesium Alloy

Due to magnesium alloy with specific strength and stiffness ratio, low density, good high damping properties, damping properties, anti-electromagnetic interference, environment-friendly materials and many other advantages, in the automotive, communications, aerospace and other fields have broad application prospects. However, conventional magnesium alloy used above120℃, the creep performance decreased rapidly, and therefore, its practical application has been greatly limited. At present, main heat resistant magnesium alloys are RE containing and magnesium matrix composites alloys, but due to the high cost, the application is limited.In this paper, by adding cheap Si element in the heat-resistant magnesium alloy Mg-8Zn-4Al-Mn(ZAM84), forming strengthening Mg2Si phase, which has property of high melting point, high hardness and elastic modulus, but the shape of Mg2Si phase in cast is coarse characters or massive, which split matrix and not conducive to improve the mechanical properties. Using ECAP deformation to improve the shape and distribution of Mg2Si phase, as well as to refine the organization, it not only can improve the performance at room temperature, but also improve the performance of high-temperature creep. Using electronic universal testing machine to test the mechanical properties of the alloy at room temperature, a high temperature creepmeter to test the high temperature performance, the method of OM, SEM, TEM, EDS, XRD, EBSD were used to detection and analysis. The results are:(1) As-cast ZAM84-2Si alloy mainly composed of a-Mg matrix, Mg2Si phase with coarse characters or massive, Bone-shaped MgZn phase, and coarse grains. The second phase of coarse and sharp edges, the average grain about100μm, after ECAPed four passes the average grain size less than10μm, and after eight passes the most of grains less than8μm, and the second coarse phase were broken into small particles dispersed uniformly in the matrix.(2) As-cast ZAM84-2Si alloy has poor mechanical properties at room temperature, the yield strength is only88MPa, tensile strength is174MPa, elongation is3.04%. Because the coarse characters Mg2Si phase split the matrix, so reduce the mechanical properties. After4-8passes ECAPed, structure refinement, the second phase was broken and dispersed uniformly, greatly improving the mechanical properties at room temperature, up to eight passes with the yield strength is93MPa, tensile strength is299MPa, elongation is14.67%.(3) In high-temperature creep test, the cast specimen at250℃,70MPa was broken momentary and almost no plastic deformation in macro-observation. After4～8passes ECAPed, creep performance is greatly improved, under the conditions of200℃,70MPa,8passes has best performance that the total strain is7.86%, steady creep rate is1.16×10-7s-1, creep life is86.39h; under the conditions of250℃, under70MPa, the total strain is8.59%, steady creep rate is6.99×10-7s-1, the creep life is16.64h.(4) After ECAPed at200～250℃, the stress within the range70-90MPa, calculated the creep hardening exponent n, ranging from5.4226to8.958, proving the mechanism of creep is dislocation climb controlling creep.