塊材的腐蝕行為
(1. 河海大學(xué) 材料科學(xué)與工程學(xué)院，南京 210098；
2. 浙江省特種設(shè)備檢驗(yàn)研究院，杭州 310020)
摘 要: 采用原位腐蝕、全浸泡腐蝕和電化學(xué)腐蝕，研究等徑角擠壓制備的超細(xì)晶AZ91D鎂合金塊材在3.5%(質(zhì)量分?jǐn)?shù))氯化鈉溶液中的腐蝕行為。結(jié)果表明：超細(xì)晶AZ91D鎂合金中α固溶體晶粒細(xì)小(1~2 μm)；鑄態(tài)組織中網(wǎng)狀β相被破碎、細(xì)化成10 μm左右的粒子，孤立且均勻分布于α固溶體上；形變細(xì)化降低合金在含氯介質(zhì)中的耐蝕性，表現(xiàn)出更嚴(yán)重的腐蝕形貌、更快的腐蝕速度、極化測(cè)試中更大的腐蝕電流密度、電化學(xué)阻抗頻譜中更小的極化電阻，且合金腐蝕行為由局部腐蝕轉(zhuǎn)變成嚴(yán)重的均勻腐蝕。引起合金塊材耐蝕性下降因素有2個(gè)：一是形變?chǔ)凉倘荏w的化學(xué)活性較高(源于應(yīng)變產(chǎn)生的大量高能晶體缺陷，如大角度晶界、高密度位錯(cuò)等)；二是細(xì)化的β相喪失了阻滯腐蝕介質(zhì)向α固溶體擴(kuò)展的屏障作用。
關(guān)鍵字: AZ91D；超細(xì)晶；等徑角擠壓；腐蝕行為
（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
