Abstract: This work aims to study the microstructural evolution of the diffusion layer and the function mechanism of La2O3 during the solid diffusion La2O3+Zn on AZ31 magnesium alloy surface. Surface solid diffusion of La2O3+Zn powder on AZ31 magnesium alloy was carried out at 390℃+4 h, the mass fractions of La2O3 in the diffusion agent was 0.0wt%, 0.2wt%, 0.4wt%, and 0.6wt%, respectively. Optical microscopy, scanning electron microscopy and X-ray diffraction were used to investigate the morphology characteristic of diffusion layer and the transformation law of phase composition with the change of La2O3 concentration. With the increase of La2O3 concentration in the diffusion agent, the microstructure of the diffusion layer was changed obviously. When there is no La2O3 in the diffusion agent, no diffusion layer appears on the surface of AZ31 magnesium alloy. When La2O3 addition was 0.2wt%, the apparent diffusion layer was observed on AZ31 magnesium alloy surface,the diffusion layer was mainly consists of Mg0.97Zn0.03+MgZn+Mg2Zn3+MgZn2. AZ31 magnesium alloy matrix was eliminated when La2O3 addition exceeded 0.4wt% and the amount of phase in the layer structure no longer changes, Mg2Zn11+Mg0.97Zn0.03+MgZn+Mg2Zn3+MgZn2 mostly existed in the diffusion layer. With the increasing La2O3 content in the diffusion agent, the diffusion layer microstructure becomes coarse, the amount of Mg0.97Zn0.03 and Mg-Zn compounds decreased and increased, respectively, the main phase in diffusion layer was MgZn. The physical diffusion model during solid diffusion La2O3+Zn on AZ31 magnesium alloy surface was built. The diffusion process is mainly the diffusion of Zn atoms, the diffusion mechanism of Zn on AZ31 magnesium alloy surface was vacancy diffusion. The microstructure evolution and function mechanism were analyzed with the different La2O3 addition in the diffusion agent, La2O3 acted as a catalyst during diffusion processing and improved the Zn diffusion activity ability. Under the same external diffusion conditions, La2O3 promoted the reaction diffusion of Zn and Mg and formed different Mg-Zn compounds.
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2020, Vol. 34 
