均匀化对EK31镁合金组织与腐蚀性能的影响

为了研究均匀化热处理对含有稀土元素Er的EK31镁合金组织及其耐蚀性能的影响,本文利用光学显微镜(OM),扫描电镜(SEM),X射线衍射仪(XRD)和化学工作站研究了铸态EK31镁合金在均匀化温度为300,400和500℃,保温时间由0.5 h至8 h热处理后的组织结构和在3.5 wt.%的Na Cl水溶液中的腐蚀行为.结果表明,EK31镁合金主要由基体α-Mg晶粒和β-Zr核相组成.经过300℃×6 h均匀化处理后,合金基体α-Mg中的β-Zr核相溶解扩散,在3.5%Na Cl水溶液中浸泡96 h后的腐蚀速率达到最低,为4.3×10-3mg/(cm2·h);当均匀化温度为400和500℃时,保温时间超过6 h后,在晶界附近富集的稀土元素Er生成Mg24Er5相,使该合金的腐蚀速率上升到1.1×10-2mg/(cm2·h).然而,与其它镁合金相比较,EK31镁合金具有优异的耐蚀性能,其原因为稀土元素Er在晶界附近形成富Er区以及Mg24Er5相的阻碍作用.

Influence of homogenization on microstructure and corrosion resistance of EK31 magnesium alloy

In order to study the effect of homogenization heat treatment on the microstructure and corrosion resistance of EK31 magnesium alloy containing rare earth element Er, the microstructures of as-cast EK31 magnesium alloy after homogenization at 300℃, 400℃ and 500℃, the holding time from 0.5 h to 8 h were observed and the electrochemical corrosion behavior of 3. 5 wt.% NaCl aqueous solutions were studied by optical microscopy ( OM ) , scanning electron microscopy ( SEM ) , X-ray diffraction ( XRD ) and electrochemical workstation. The results show that the as-cast EK31 alloy was mainly composed ofα-Mg grains and β-Zr core phases. After homogenization at 300 ℃×6 h, the β-Zr core phase was dissolved and diffused in the alloy matrix. The corrosion rate of the solution was 4.3×10-3 mg/(cm2·h) after being immersed in 3.5%NaCl solution for 96 h. When the temperature was 400℃ and 500℃ abd the holding time was more than 6 h, the rare earth element Er was enriched near the grain boundary and generated a large amount of Mg24 Er5 phase, leading to an increase of the corrosion rate of the alloy to 1.1×10-2 mg/(cm2·h). However, compared with other magnesium alloys, it has excellent corrosion resistance. The reason is that the hindrance of the rare earth element Er and Mg24 Er5 phase in the vicinity of the grain boundary.