AZ91D镁合金激光熔覆Al-Si涂层微观组织及热力学分析

Microstructure evolution and thermodynamic analysis of laser claded Al-Si coating on AZ91D Alloy

关键词:  镁合金  激光熔覆  微观组织  涂层

Key words:  magnesium alloy  laser cladding  microstructure  coating

摘要:

以Al-Si共晶成分合金粉末为熔覆材料在AZ91D镁合金表面进行了激光熔覆试验.采用光学显微镜、扫描电镜、能谱仪、X射线衍射仪分析了涂层的微观组织,并利用Thermo-Calc软件分析了涂层的相组成、相成分及结晶转变过程.结果表明,涂层微观组织分为两层,上半层为Al₁₂Mg₁₇基体上均匀分布着Mg₂Si树枝晶和细小的Al₃Mg₂针状相,其结晶过程为液相→液相+Mg₂Si→Mg₂Si+Al₁₂Mg₁₇→Mg₂Si+Al₁₂Mg₁₇+Al₃Mg₂;下半层由Mg₂Si颗粒、α-Mg树枝晶和(α-Mg+Al₁₂Mg₁₇)共晶组织组成,其结晶过程为液相→液相+Mg₂Si→液相+Mg₂Si+α-Mg→Mg₂Si+α-Mg+(α-Mg+ Al₁₂Mg₁₇)共晶组织.研究结果对AZ91D合金表面激光熔覆Al-Si合金涂层微观组织及其转变过程分析具有指导意义.

Abstract:

Laser cladding was used to prepare Al-Si coating on AZ91D magnesium alloy by using Al-Si eutectic alloy powders. Microstructure of the coatings was analyzed by optical microscope, scanning electronic microscope, energy dispersive spectroscopy and X-ray diffractometer. The phase constitution, composition and transformation in the coating were analyzed with Thermo-Calc software. The results showed that the coating was divided into two layers. In the upper layer, Mg₂Si dendrites and fine needle-like Al₃Mg₂ are uniformly distributed on Al₁₂Mg₁₇ matrix and its crystallization process is liquid→liquid+Mg₂Si→ Mg₂Si+Al₁₂Mg₁₇→Mg₂Si+Al₁₂Mg₁₇+Al₃Mg₂. The bottom layer consists of Mg₂Si particles, α-Mg dendrites and(α-Mg+A₁₂M₁₇) eutectics and its crystallization process is liquid→liquid+Mg₂Si→liquid+Mg₂Si+α-Mg→Mg₂Si+α-Mg+(α-Mg+A₁₂M₁₇) eutectics. The calculated results are well consistent with the experimental data and it is beneficial to understanding the microstructure evolution of laser claded Al-Si coating on AZ91D magnesium alloy.