Effects Of Ca Addition And Hot Compression On Microstructure And Texture Of Mg-1.0Zn Alloy

In this paper, Mg-1.0wt.%Zn-1.5wt.%Ca(ZX115) magnesium alloy was designed and fabricated. Mg-1.0wt.%Zn(Z1) magnesium alloy was also fabricated as a contrast. The plastic deformation behavior of ZX115 magnesium alloy during the uniaxial hot compression was studied by X-ray Fluorescence Spectrometry(XRF), Optical Microscope(OM), Electron Backscattered Diffraction(EBSD), Energy Spectrum(EDS), X-ray Diffraction(XRD) and so on. The effects of deformation conditions and Ca element on dynamic recrystallization(DRX) and deformation texture were mainly investigated. The plastic deformation constitutive equations were proposed according to the hot compression stress-strain curves. The main research results of this study are as follows:(1) The nucleation mechanism of DRX exhibits a strong dependence on deformation temperature. At a low temperature( <350℃), twins are observed and the very small recrystallized grains are observed at these twins boundaries and the original grain boundaries. At a high temperature(≥350℃), the small dynamical recrystallized grains nucleate at the original grain boundaries and then grow up. In addition, whether high or low temperatures, the second phase particles can promote the nucleation of DRXed grains;(2) The recrystallized microstructure of ZX115 after hot compression is composed of equiaxed grains with different sizes. With the increasing deformation temperature, the DRX process become more complete and the microstructure become more uniform, however, the recrystallized grains become coarse. The nucleation rate of DRX increases as the strain rate increases, resulting in the grain refinement. The element Ca in magnesium alloys forms the second phase particles containing Ca which accelerate the DRX of ZX115 alloy.(3) The(0001) basal texture of ZX115 alloy turns to different directions with a wide diffusion and low intensity after hot compression. With the increase of strain rate, the deformation texture become more random and weaker. The DRX behavior during hot compression can greatly weaken the texture of magnesium alloy, due to the randomness of nucleation and growth during DRX process.(4) The addition of Ca element decreases the c/a ration and then enhances the lattice symmetry of magnesium alloy, leading to an easier activation of prismatic slip and pyramidal slip. The widely distributed Ca-rich second phase in ZX115 alloy promote the DRX and then weaken the texture.(5) The relationship between strain rate, stress and temperature can be predicted by a constitutive law, A[sinh(ασ)]n= exp[Q/(RT)], with Q=172.71kJ/mol, α=0.0157MPa-1,n=3.5; The relationship between the deformation conditions(Z parameter) and peak strain can be given by an equation εp=1.1×10-5 Z 0.30.