固溶时效处理对Mg-4Sm-3Gd-0.5Zr合金显微组织和耐蚀性能的影响

利用光学显微镜、X射线衍射仪和扫描电镜等方法研究了固溶时效处理前后Mg-4Sm-3Gd-0.5Zr合金(质量分数,%)的显微组织、物相组成和腐蚀形貌,并在质量分数为3.5%的NaCl溶液中进行了静态失重和电化学测试。结果表明,铸态Mg-4Sm-3Gd-0.5Zr合金由α-Mg基体和沿晶界分布的粗大网状共晶相Mg₄₁Sm₅和Mg₅Gd组成,固溶时效处理并没有改变共晶相的种类,但网状共晶组织消失,并且晶内有大量细小弥散的第二相析出,晶界更加清晰。试验合金采用525 ℃×8 h固溶+225 ℃×8 h时效处理后,腐蚀速率从0.185 mg·cm^-2·h^-1降低至到0.116 mg·cm^-2·h^-1,自腐蚀电流密度从1.599×10^-4A·cm^-2降低到0.924×10^-4 A·cm^-2,耐蚀性能明显提高。

Effect of solution and aging treatment on microstructure and corrosion resistance of Mg-4Sm-3Gd-0.5Zr alloy

Microstructure, phase composition and corrosion morphology of Mg-4Sm-3Gd-0.5Zr (mass fraction, %) alloy before and after solution and aging treatment were studied by means of optical microscope, X-ray diffractometer and scanning electron microscope, and the static weight loss experiment and electrochemical test were carried out in NaCl solution with mass fraction of 3.5%. The results show that the as-cast Mg-4Sm-3Gd-0.5Zr alloy is composed of α-Mg matrix and coarse network eutectic phases Mg₄₁Sm₅ and Mg₅Gd distributed along grain boundaries. After solution and aging treatment, the type of eutectic phases is not changed, but the network eutectic microstructure disappears, a large number of fine and dispersed second phases are precipitated in the grain and the grain boundaries are clearer. After solution treated at 525 ℃ for 8 h and aged at 225 ℃ for 8 h, the corrosion rate of the alloy decreases from 0.185 mg·cm^-2·h^-1 to 0.116 mg·cm^-2·h^-1, and the corrosion current density decreases from 1.599×10^-4 A·cm^-2 to 0.924×10^-4 A·cm^-2, at which the corrosion resistance is significantly improved.