Mechanical Properties of Gradient Structure Mg Alloy
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Mechanical Properties of Gradient Structure Mg Alloy HONGLIANG CHEN, JIANG YANG, HAO ZHOU, JORDAN MOERING, ZHE YIN, YULAN GONG, and KUNYU ZHAO In this work, a surface mechanical attrition treatment (SMAT) process was applied to AZ31B magnesium alloy at room temperature. This method produced a gradient structure on the treated AZ31B, in which the grains of the topmost layer are refined to nanoscale sizes. A combination of nanocrystallites at the surface and coarse-grains in the center are the main features of this structure. This structure results in an excellent combination of both strength and ductility. The highest yield strength for the 30 minutes SMAT AZ31B samples increased to 249 ± 5 MPa and the uniform elongation decreased to 9.3 ± 0.8 pct, whereas the original yield strength was only 147 ± 4 MPa and the uniform elongation was 15.4 ± 1.1 pct. Microstructural observations, stress relaxation tests, and hardness tests were used to verify the results. Additionally, there is a specific volume fraction of gradient structure to achieve the best mechanical performance, which is shown to be in the range of 9.3 to 14 pct for the AZ31B alloy. DOI: 10.1007/s11661-017-4216-5 The Minerals, Metals & Materials Society and ASM International 2017
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INTRODUCTION
MAGNESIUM and its alloys possess many excellent properties, such as heat dissipation, electro-magnetic shielding capabilities, and a low density. However, the poor mechanical properties and cold working capabilities of magnesium and its alloys significantly narrows their applications due to the limited number of slip systems in the less symmetric HCP crystal structure. Many studies have focused on methods to enhance the mechanical properties of magnesium and its alloys, especially enhancing its strength. Over the past several decades, severe plastic deformation (SPD) methods such as accumulative rolling-bonding (ARB),[1] cyclic extrusion compression (CEC),[2–4] equal channel angular pressing (ECAP),[5–7] high pressure torsion (HPT),[8] and twist extrusion (TE)[9] were developed to produce ultra-fine-grained or nanocrystalline materials, which exhibit unprecedented high strengths due to the Hall– Petch effect. However, in most cases, these (SPD) technologies almost always lead to dramatic reductions in ductility. It is challenging for the community to
HONGLIANG CHEN, JIANG YANG, ZHE YIN, YULAN GONG, and KUNYU ZHAO are with the Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming, Yunnan 650093, China. Contact e-mail: [email protected] HAO ZHOU is with the Institute of Microstructures and Properties of Advanced Materials in Beijing University of Technology, Beijing 100124, China. JORDAN MOERING is with the Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695. Manuscript submitted January 16, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
process structural materials with increased strength without sacrificing much of the ductility. Recently, surface mechanical attrition trea
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