AZ31镁合金固态扩渗La2O3+Zn渗层组织演化过程研究

Study on the Diffusion Layer Microstructure Evolution Process of AZ31 Magnesium Alloy by Solid Diffusion La 2O 3+Zn

通过在AZ31镁合金表面固态扩渗La 2O 3+Zn,研究扩渗层的组织演化特征,揭示La 2O 3在扩渗过程中的作用机理。对AZ31镁合金在390℃下进行4 h的表面固态扩渗La 2O 3+Zn粉末,La 2O 3在扩渗剂中的质量分数分别为0.0%、0.2%、0.4%、0.6%。通过光学显微镜、扫描电镜和X射线衍射仪,研究随La 2O 3含量的变化,渗层的形貌特征和物相组成的变化规律。随扩渗剂中La 2O 3含量的增加,渗层组织发生了明显的变化。当扩渗剂中无La 2O 3时,AZ31镁合金表面无渗层出现;当扩渗剂中La 2O 3的质量分数为0.2%时,在AZ31镁合金表面可观察到有明显的渗层,渗层主要由Mg 0.97 Zn 0.03+MgZn+Mg 2Zn 3+MgZn 2组成。当La 2O 3在扩渗剂中的质量分数超过0.4%以后,AZ31镁合金基体消失,渗层组织中的物相不再发生变化,Mg 2Zn 11+Mg 0.97 Zn 0.03+MgZn+Mg 2Zn 3+MgZn 2主要存在于渗层中。随扩渗剂中La 2O 3含量的增加,渗层组织变得粗大,Mg 0.97-Zn 0.03和Mg-Zn化合物分别减少和增加,渗层中主要物相为MgZn。建立了AZ31镁合金表面固态扩渗La 2O 3+Zn粉末的扩散物理模型,扩渗过程中主要是Zn原子的扩散,Zn在AZ31镁合金表面的扩散机制为空位扩散。分析了扩渗剂中不同含量的La 2O 3渗层的组织演化和作用机理,发现La 2O 3在扩渗过程中起到了催化剂的作用,增强了Zn原子的活动能力,在相同的外界扩渗条件下,La 2O 3促进了Zn与Mg发生反应从而扩散形成不同的Mg-Zn化合物。

This work aims to study the microstructural evolution of the diffusion layer and the function mechanism of La 2O 3 during the solid diffusion La 2O 3+Zn on AZ31 magnesium alloy surface.Surface solid diffusion of La 2O 3+Zn powder on AZ31 magnesium alloy was carried out at 390℃+4 h,the mass fractions of La 2O 3 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 La 2O 3 concentration.With the increase of La 2O 3 concentration in the diffusion agent,the microstructure of the diffusion layer was changed obviously.When there is no La 2O 3 in the diffusion agent,no diffusion layer appears on the surface of AZ31 magnesium alloy.When La 2O 3 addition was 0.2wt%,the apparent diffusion layer was observed on AZ31 magnesium alloy surface,the diffusion layer was mainly consists of Mg 0.97 Zn 0.03+MgZn+Mg 2Zn 3+MgZn 2.AZ31 magnesium alloy matrix was eliminated when La 2O 3 addition exceeded 0.4wt%and the amount of phase in the layer structure no longer changes,Mg 2Zn 11+Mg 0.97 Zn 0.03+MgZn+Mg 2Zn 3+MgZn 2 mostly existed in the diffusion layer.With the increasing La 2O 3 content in the diffusion agent,the diffusion layer microstructure becomes coarse,the amount of Mg 0.97 Zn 0.03 and Mg-Zn compounds decreased and increased,respectively,the main phase in diffusion layer was MgZn.The physical diffusion model during solid diffusion La 2O 3+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 La 2O 3 addition in the diffusion agent,La 2O 3 acted as a catalyst during diffusion processing and improved the Zn diffusion activity ability.Under the same external diffusion conditions,La 2O 3 promoted the reaction diffusion of Zn and Mg and formed different Mg-Zn compounds.