Microstructure evolution and mechanical properties of the ZM61 alloy sheets under different pre-rolling and high strain
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Microstructure evolution and mechanical properties of the ZM61 alloy sheets under different pre-rolling and high strain rate rolling temperatures Hongge Yan1,2, Qin Wu1,2,a), Jihua Chen1,2,b), Weijun Xia1,2, Min Song3, Bin Su1,2, Jiang Wu1,2 1
School of Materials Science and Engineering, Hunan University, Changsha 410082, PR China Hunan Provincial Key Laboratory of Spray Deposition Technology & Application, Hunan University, Changsha 410082, PR China 3 State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, PR China a) Address all correspondence to these authors. e-mail: [email protected] b) e-mail: [email protected] 2
Received: 20 February 2020; accepted: 2 June 2020
The microstructure evolution, dynamic recrystallization (DRX) and precipitation of the ZM61 alloy sheets prepared with different rolling conditions were studied. The DRX grain sizes (dDRX) at four high strain rate rolling (HSRR) temperatures (275–350 °C) are 1.9, 2.3, 2.6 and 3.1 μm, respectively, while the DRX volume fractions ( fVDRX) are 69, 73, 76 and 82%, respectively. 300 °C is selected as the optimal HSRR temperature. The dDRX and fVDRX of the alloys prepared by pre-rolling (PR) at 300 °C + HSRR are 1.0 μm and 91%, respectively. The PR treatment does not change the types of the precipitates but promotes the precipitation. The tensile strength (UTS) of 369 MPa and yield strength (YS) of 261 MPa can be achieved by HSRR at 300 °C, while a further increase in both UTS and YS can be obtained by PR treatment.
Introduction Mg alloys have a broad application prospect in automobile manufacture, aerospace and other fields due to their high specific strength and low density [1]. However, their industrial applications are severely limited by the poor formability, the difficulties in the subsequent deep processing and the disadvantages in mechanical properties as compared with Al and steel [2]. Grain refinement and precipitation strengthening are two promising means to improve the comprehensive mechanical properties of wrought Mg alloys [3, 4]. The temperature is an important factor in the recrystallization process, as it is a typical thermal activation process [5]. Peng et al. [6] have found that the critical strain of dynamic recrystallization (DRX) in the Mg–6Zn–1Mn alloy increases with the decreasing compression temperature, indicating that the lower temperature is unfavorable to DRX. DRX becomes easier with the increasing compression temperature, while the coarser DRX grains are obtained. The ultra-fine-grained Mg alloy sheets with high strength and plasticity have been successfully prepared by high strain rate rolling (HSRR) in our previous work [7]. However, the initial thickness of Mg alloy sheets for HSRR is relatively thin, which is not conducive to the
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industrial production. Moreover, the DRX degree should be further improved. Zhu et al. [8] have revealed that twinning would replace the dislocation slip as the main deformation mechanism during HSRR at the strain rate of 9
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