Influence of Microstructure Heterogeneity on the Corrosion Resistance and Microhardness of 5052 Al-Mg Alloy
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https://doi.org/10.1007/s11837-020-04364-5 Ó 2020 The Minerals, Metals & Materials Society
ADVANCES IN SURFACE ENGINEERING
Influence of Microstructure Heterogeneity on the Corrosion Resistance and Microhardness of 5052 Al-Mg Alloy PENG ZHOU,1 LEI DENG,1 PENG GUO,1 WEI RAO,1 XINYUN WANG,1 and MAO ZHANG 1,2 1.—State Key Laboratory of Materials Processing and Die & Mould Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, Hubei, China. 2.—e-mail: [email protected]
In this study, the high-pressure torsion (HPT) process was adopted to produce microstructure heterogeneity in a 5052 Al-Mg alloy. The influences of microstructural heterogeneity on the corrosion resistance and microhardness were characterized. The results show that, compared with the annealed samples, the microhardness is significantly increased and corrosion resistance is reduced by HPT treatment. Due to the massive formation of high-angle grain boundaries (HAGBs), which provide nucleation sites for pitting corrosion, grain refining induced by HPT will reduce the corrosion resistance of 5052 Al-Mg alloy. Meanwhile, when the fractions of HAGBs are similar, compared to heterogeneous materials, the corrosion resistance of materials with homogenous microstructures is better. Key words: High-pressure torsion, Heterogeneity, Corrosion resistance, Microstructure, Microhardness, Al-Mg alloy
INTRODUCTION Due to their medium-to-high strength, good weldability, favorable formability, and strong corrosion resistance, Al-Mg alloys have been widely applied in marine and naval applications.1–4 With the fast development of the marine industry, the requirements for high strength and strong corrosion resistance become harsher. Hence, the strengthening of Al-Mg alloys becomes an urgent issue. Because of the increase in the number of grain boundaries, the ultra-fine grain (UFG) materials have prominent strength and good ductility.5–7 Hence, generating UFG in materials has become an essential approach for strengthening. Currently, methods based on severe plastic deformation (SPD), including high-pressure torsion (HPT), equal channel angular pressing (ECAP), and accumulative rollbonding (ARD), are common ways to obtain UFG materials.8–10 Among them, HPT is the most effective one and has the smallest dimension limit.11 Due
(Received May 15, 2020; accepted August 25, 2020)
to the nature of torsion, HPT is prone to producing UFG materials with microstructure heterogeneities.12,13 That is, under small torsion cycles, the shear strain increases with the distance to the torsion axis, and the refining degree increases accordingly. Nevertheless, this microstructure heterogeneity will disappear after the torsion cycles further increases. As reported by Wu et al.14,15 a certain degree of microstructure heterogeneity is beneficial to the coherent increase of strength and ductility. The grain size gradients can cause macroscopic strain gradients, promoting the accumulation and interaction of dislocat
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