Effect of Sc and Zr Additions on Recrystallization Behavior and Intergranular Corrosion Resistance of Al-Zn-Mg-Cu Alloys.

Peng Xia,Yiwang Jia,Shuncheng Wang,Nan Zhou,Huilan Huang,Dongfu Song

doi:10.3390/ma14195516

Peng Xia, Yiwang Jia + Show 4 more

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https://doi.org/10.3390/ma14195516

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Abstract

The recrystallization and intergranular corrosion behaviors impacted by the additions of Sc and Zr in Al-Zn-Mg-Cu alloys are investigated. The stronger effect of coherent Al3(Sc1−xZrx) phases on pinning dislocation resulted in a lower degree of recrystallization in Al-Zn-Mg-Cu-Sc-Zr alloy, while the subgrain boundaries can escape from the pinning of Al3Zr phases and merge with each other, bringing about a higher degree of recrystallization in Al-Zn-Mg-Cu-Zr alloy. A low degree of recrystallization promotes the precipitation of grain boundary precipitates (GBPs) with a discontinuous distribution, contributing to the high corrosion resistance of Al-Zn-Mg-Cu-Sc-Zr alloy in the central layer. The primary Al3(Sc1−xZrx) phase promotes recrystallization due to particle-stimulated nucleation (PSN), and acts as the cathode to stimulate an accelerated electrochemical process between the primary Al3(Sc1−xZrx) particles and GBPs, resulting in a sharp decrease of the corrosion resistance in the surface layer of Al-Zn-Mg-Cu-Sc-Zr alloy.

Highlights

IntroductionTo enhance the corrosion resistance, one commonly used method is to acquire the anti-corrosion precipitated microstructure by heat processing, such as the over aging or multi-step aging heat treatments
Al-Zn-Mg-Cu series alloys are widely used as aeronautical materials mainly because of their high specific strengths and fracture toughness [1,2,3]. This series of aluminum alloys is highly susceptible to intergranular corrosion (IGC), exfoliation corrosion (EXCO) and stress corrosion crack (SCC) [4,5,6]
The composite addition of SC and Zr could bring about a remarkable grain refinement and effectively inhibit recrystallization

Summary

Introduction

To enhance the corrosion resistance, one commonly used method is to acquire the anti-corrosion precipitated microstructure by heat processing, such as the over aging or multi-step aging heat treatments Through these heat treatments, coarsening precipitates and the grain boundary phases (GBPs) with a discontinuous distribution can be obtained, effectively improving the corrosion properties based on either anodic oxidation or hydrogen embrittlement theories [7,8,9,10]. Another method is to inhibit the recrystallization process of deformed aluminum, because the low-angle grain boundaries (LAGBs) within non-recrystallized grains are more resistant to corrosion than the high-angle grain boundaries (HAGBs) within recrystallized grains [11,12]. The addition of minor elements such as Sc and Zr can be used for recrystallization inhibition and can promote the improvement of corrosion resistance, which has been continuously reported in the recent literature [13,14,15,16]

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