Ca对铸态Mg-4Zn合金组织及腐蚀性能的影响

Effect of Ca on microstructure and corrosion resistance of as-cast Mg-4Zn alloy

为开发生物医用镁合金,利用高纯原材料,在氩气气氛保护下熔炼浇铸制备了Ca合金化的Mg-4Zn合金(Ca含量分别为0.4%和1.0%,质量分数)。通过OM、SEM以及XRD分析了合金的微观组织和相组成,采用析氢法、腐蚀质量损失法以及电化学法测试了合金在Hanks模拟体液中的腐蚀行为。结果表明,合金由初生Mg固溶体和共晶体组成;随Ca含量增加,合金的电荷传递电阻减小,自腐蚀电位下降,自腐蚀电流密度增加;析氢法和腐蚀质量损失法均表明合金的腐蚀速率随时间延长而减小。共晶体对合金的耐蚀性有影响;当Ca含量从0.4%增加到1.0%时,共晶体含量增加,促进了合金的电偶腐蚀,合金耐蚀性降低。Mg-4Zn-(0.4,1)Ca合金的腐蚀形式主要为晶间腐蚀和点蚀。

In order to develop a biomedical magnesium alloy,Mg-4Zn alloys doped with 0. 4% Ca and 1% Ca were fabricated by conventional gravity casting under protection of argon gas. Microstructure and phase composition of the alloys were investigated by optical microscope,scanning electron microscopy and X-ray diffraction. Corrosion behavior in Hanks simulated body fluid was studied by hydrogen-evolution test,mass-loss test and electrochemical test. The results indicate that the alloys are composed of magnesium solid solution and eutectic phase. As Ca content increasing,the charge-transfer resistance and free-corrosion potential of the alloy decrease;whereas the corrosion current density increasing. Hydrogen-evolution and mass-loss test indicates that corrosion rate decreases with the increasing time. Eutectic has an influence on corrosion of the alloys,as Ca increasing from 0. 4% to 1%,eutectic content increases which is helpful to improve galvanic corrosion,and thus results in a decrease of the corrosion resistance. The corrosion behaviors of Mg-4Zn-( 0. 4,1) Ca alloys are mainly caused by pitting corrosion and intergranular corrosion.