Designing High Corrosion Resistant Peritectic Magnesium Alloys via Sc and Y Addition
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INTRODUCTION
MAGNESIUM (Mg) alloys are considered one of the candidates for engineering applications in the automobile and aeronautical industry, owing to their good castability and high strength-to-weight ratio (specific strength).[1–4] However, the poor corrosion resistance of these alloys has significantly restricted their application.[5–10] Mg is quite susceptible to corrosion due mainly to its negative potential (~ 2.37 VSHE)[11] and low Pilling–Bedworth (P–B) ratio (< 1).[12,13] These factors are conducive for the occurrence of galvanic corrosion and hinder the formation of a protective passive film on the alloys surface. Previous studies[12,14–16] have demonstrated improvements in the corrosion performance of Mg by controlling micro-galvanic corrosion, i.e., by designing a single-phase Mg alloy. To mimic the designing concept PENGYU ZHAO, TIAN XIE, and XINMEI XU are with the National Engineering Research Center of Light Alloy Net Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. HONG ZHU is with the University of Michigan - Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, P.R. China and also with the State Key Lab of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. FUYONG CAO is with the Center for Marine Materials Corrosion and Protection, College of Materials, Xiamen University, Xiamen 361005, P.R. China. TAO YING is with the National Engineering Research Center of Light Alloy Net Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University. Contact email: [email protected] XIAOQIN ZENG is with the National Engineering Research Center of Light Alloy Net Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University and also with the State Key Lab of Metal Matrix Composites, Shanghai Jiao Tong University. Contact email: [email protected] Manuscript submitted November 12, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
of stainless steel, the development of ‘‘stainless’’ Mg alloy must satisfy three requirements, namely (i) the alloying elements should exhibit high solid solubility in Mg, thereby resulting in maximum enhancement of the solid solution strengthening and the passivation behavior of the elements. (ii) The alloying elements should form a protective corrosion layer. The P–B ratio of the added elements, which elucidates the coverage integrity of the passive films on the surface of the alloys, should be higher than 1. (iii) The differences in electrode potential between the alloying element (M)-rich zone and depleted zone should be small, so as to reduce the susceptibility of the alloy to corrosion. Based on the aforementioned three requirements, a summary of the potential alloying elements is presented[17–20] in Figure 1. Among these elements, scandium (Sc) appears to be a potential choice for designing Mg alloys with high corrosion resistance. Additionally, compared with other rare earth elements, Sc yield
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