块材的腐蚀行为
(1. 河海大学 材料科学与工程学院，南京 210098；
2. 浙江省特种设备检验研究院，杭州 310020)
摘 要: 采用原位腐蚀、全浸泡腐蚀和电化学腐蚀，研究等径角挤压制备的超细晶AZ91D镁合金块材在3.5%(质量分数)氯化钠溶液中的腐蚀行为。结果表明：超细晶AZ91D镁合金中α固溶体晶粒细小(1~2 μm)；铸态组织中网状β相被破碎、细化成10 μm左右的粒子，孤立且均匀分布于α固溶体上；形变细化降低合金在含氯介质中的耐蚀性，表现出更严重的腐蚀形貌、更快的腐蚀速度、极化测试中更大的腐蚀电流密度、电化学阻抗频谱中更小的极化电阻，且合金腐蚀行为由局部腐蚀转变成严重的均匀腐蚀。引起合金块材耐蚀性下降因素有2个：一是形变α固溶体的化学活性较高(源于应变产生的大量高能晶体缺陷，如大角度晶界、高密度位错等)；二是细化的β相丧失了阻滞腐蚀介质向α固溶体扩展的屏障作用。
关键字: AZ91D；超细晶；等径角挤压；腐蚀行为
（1. College of Materials Science and Engineering, Hohai University, Nanjing 210098, China;
2. Zhejiang Special Equipment Inspection and Research Institute, Hangzhou 310020, China）
Abstract:The corrosion behavior of the equal-channel angular pressed (ECAPed) bulk AZ91D Mg alloy in 3.5% (mass fraction) NaCl solution was investigated by optical/electron microscopy observation, in-situ corrosion observation, constant immersion tests and electrochemical measurements. The results show that the ECAPed AZ91D with fine grain size (1−2 μm) obtains α-phase matrix, and the original net-like coarse β-phase is broken into uniformly distributed fine β-phase particles with a size of about 10 μm. The corrosion resistance of the ultra-fine grained (UFG) AZ91D Mg alloy is obviously weakened, with more severe corrosion damaged morphologies, higher corrosion rates, larger corrosion current density in the polarization curves and lower fitted corrosion resistances in the EIS plots. Due to the homogenously distributed fine β-phase particles, the UFG AZ91D Mg alloy presents a trend of change from localized corrosion into severely uniform corrosion. Two factors lead to the weakness in the corrosion resistance of the UFG AZ91D alloy. One is ECAP deformed α-phase matrix with more corrosion activation, resulting from strain-induced crystalline defects (e.g., energetic high-angle grain boundaries and dislocations). The other is ECAP refined β-phase, providing no barrier to the corrosion propagation in α-phase matrix.
Key words: AZ91D; ultra-fine grain; equal channel angular pressing; corrosion behavior
