Enhancing Thermal Stability of Binary Al-Mg Alloys by Tailoring Grain Orientations Using a High Solute Mg Content
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INTRODUCTION
DUE to the excellent corrosion resistance, weldability, and high specific strength, heavily deformed Al-Mg alloys have great potential for structural applications.[1,2] The addition of Mg in Al matrix can enhance the multiplication of dislocations and suppress dynamic recovery/recrystallization, and hence promote grain refinement and stabilize grain size effectively during deformation. For example, the grain size of highpressure torsion (HPT)-deformed materials decreases from ~ 800 to ~ 150 nm with the Mg content increasing from 0 to 3 wt pct.[3,4] As a result, heavily deformed AlMg alloys have plenty of grain boundaries (GBs)/ interfaces and a high dislocation density. In addition,
MIN ZHA and HUI-YUAN WANG are with the State Key Laboratory of Super Hard Materials, Jilin University, Changchun, 130012, P.R. China and also with the Key Laboratory of Automobile Materials of Ministry of Education & School of Materials Science and Engineering, Nanling Campus, Jilin University, No. 5988 Renmin Street, Changchun 130025, P.R. China, and also with the International Center of Future Science, Jilin University, Changchun 130012, P.R. China. Contact e-mail: [email protected] XIANG-TAO MENG, ZHI-YUAN YU, HONG-MIN ZHANG, HAO-LIANG YIN, QING-QUAN ZHANG, and QI-CHUAN JIANG are with the Key Laboratory of Automobile Materials of Ministry of Education & School of Materials Science and Engineering, Nanling Campus, Jilin University. CHENG WANG is with the State Key Laboratory of Super Hard Materials, Jilin University and also with the Key Laboratory of Automobile Materials of Ministry of Education & School of Materials Science and Engineering. Manuscript submitted January 17, 2019. Article published online August 28, 2019 5264—VOLUME 50A, NOVEMBER 2019
GBs induced by severe plastic deformation (SPD) usually exist in a relatively high energetic state because of their disordered atomic arrangement. Therefore, deformed Al-Mg alloys have a relatively strong tendency to reduce the total GB area to diminish GB energy, and thus exhibit a low thermal stability.[5] According to the literature on thermal stability of ultrafine grained (UFG) Al-Mg alloys, ultrafine grains in Al-Mg alloys often coarsen rapidly to several micrometers with a starting grain size of 100 to 200 nm, depending on SPD processes and Mg contents.[6–8] To improve the thermal stability, a number of approaches have been proposed, and they can be classified into two categories: kinetic stabilization and thermodynamic stabilization strategies.[9,10] The kinetic stabilization strategies are mainly implemented by obstructing GB movement and thus promoting grainsize stabilization, such as solute drag.[5,11–14] A high solute concentration in GBs and a low mobility of solute atoms are expected to produce a large drag force and strong kinetic stabilization. Mg atoms, easily segregating on GBs during deformation, can suppress dislocation recovery and slow down GB migration rate.[15,16] Zhou et al. reported that the segregation of Mg solute has a very large effect in red
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