挤压温度及路径对Mg-Gd-Y-Zn-Zr合金等通道角挤压组织及性能影响
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摘要
以Mg-13Gd-4Y-2Zn-0. 6Zr镁合金为研究对象进行等通道转角挤压实验,研究了挤压温度以及挤压路径对Mg-Gd-YZn-Zr镁合金的微观组织和力学性能的影响。结果表明,350℃挤压温度下晶粒未发生明显的细化; 400和450℃挤压温度时形变晶粒晶界处发生动态再结晶,晶粒发生细化; 500℃挤压温度时晶界已部分熔化,导致晶界弱化。450℃挤压温度下,铸态和均匀态试样经过1p-ECAP挤压后,在粗大形变晶粒晶界先发生动态再结晶,粗大晶粒和动态再结晶晶粒共存形成双峰组织。均匀态试样1p-ECAP挤压后屈服强度和抗拉强度均提高,屈服强度由145. 0 MPa提高到175. 6 MPa,抗拉强度由254. 3 MPa提高到294. 7 MPa。由于存在双峰组织,细小的动态再结晶晶粒和粗大形变晶粒之间在拉伸过程中变形不协调,容易引起应力集中,导致断裂伸长率降低。A路径4p-ECAP挤压后晶粒细化不均匀,挤压试样不同部位的材料性能存在一定差异; BC路径挤压时由于在下一道次挤压时都转动角度,滑移面出现交叉,晶粒细化比较均匀,挤压试样的屈服强度、抗拉强度和伸长率较高。
The equal channel angular pressing( ECAP) experiments were conducted on Mg-13 Gd-4 Y-2 Zn-0. 6 Zr magnesium alloy to investigate the effects of extrusion temperature and extrusion route on microstructure evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy. The experimental results show that the grains are refined insignificantly at 350 ℃ and dynamic recrystallization( DRX) occurs at the deformed grains boundaries at 400 and 450 ℃ where the grains are refined. Furthermore,the grain boundaries are partially melted at500 ℃,which weaken the grain boundaries. After 1 p-ECAP of as-cast and homogenized samples at extrusion temperature of 450 ℃,the DRX occurs firstly in the coarse deformed grains boundaries,and the bimodal microstructure is formed for the coarse grains are surrounded with finer DRX grains. The tensile yield strength increases from 145. 0 MPa to 175. 6 MPa and the ultimate tensile strength increases from254. 3 MPa to 294. 7 MPa respectively after 1 p-ECAP for the homogenized sample,while the fracture elongation decreases for the existence of bimodal microstructure which causes the stress concentration at the interface of coarse deformed grains and finer DRX grains. The grain sizes of the samples are uneven after 4 p-ECAP through A route,which brings the mechanical property differences in different parts of the extrusion samples. The grain sizes are evenly finer through Bc route due to the rotation of extruded sample and occurrence of dislocationcross slip after each pass,which results in higher tensile yield stress,ultimate tensile stress and fracture elongation.
The equal channel angular pressing( ECAP) experiments were conducted on Mg-13 Gd-4 Y-2 Zn-0. 6 Zr magnesium alloy to investigate the effects of extrusion temperature and extrusion route on microstructure evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy. The experimental results show that the grains are refined insignificantly at 350 ℃ and dynamic recrystallization( DRX) occurs at the deformed grains boundaries at 400 and 450 ℃ where the grains are refined. Furthermore,the grain boundaries are partially melted at500 ℃,which weaken the grain boundaries. After 1 p-ECAP of as-cast and homogenized samples at extrusion temperature of 450 ℃,the DRX occurs firstly in the coarse deformed grains boundaries,and the bimodal microstructure is formed for the coarse grains are surrounded with finer DRX grains. The tensile yield strength increases from 145. 0 MPa to 175. 6 MPa and the ultimate tensile strength increases from254. 3 MPa to 294. 7 MPa respectively after 1 p-ECAP for the homogenized sample,while the fracture elongation decreases for the existence of bimodal microstructure which causes the stress concentration at the interface of coarse deformed grains and finer DRX grains. The grain sizes of the samples are uneven after 4 p-ECAP through A route,which brings the mechanical property differences in different parts of the extrusion samples. The grain sizes are evenly finer through Bc route due to the rotation of extruded sample and occurrence of dislocationcross slip after each pass,which results in higher tensile yield stress,ultimate tensile stress and fracture elongation.
引文
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[4]邓永和.稀土镁合金研究现状与发展趋势[J].稀土,2009,30(1):76-79.DENG Yonghe. Research progress and development trend in MgRE alloys[J]. Chinese Rare Earth,2009,30(1):76-79.
[5] YANG Q,XIAO B L,ZHANG Q,et al. Exceptional high-strainrate superplasticity in Mg-Gd-Y-Zn-Zr alloy with long-period stacking ordered phase[J]. Scripta Materialia,2013,69(11-12):801-804.
[6]高岩. Mg-Y-Gd-Zn-Zr镁合金组织、性能及其蠕变行为研究[D].上海:上海交通大学,2009.GAO Yan. Microstructure,properties and creep behavior of MgGd-Y-Zn-Zr alloys[D]. Shanghai:Shanghai Jiao Tong University,2009.
[7] KIM B,BEAK S M,LEE J H,et al. High-strain-rate superplasticity of fine-grained Mg-6Zn-0. 5Zr alloy subjected to low-temperature indirect extrusion[J]. Scripta Materialia, 2017, 141:138-142.
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[9] BRUDER E,GANGARAJU C,LAPOVOK R. Reformation uniformity control of complex curved part during hydroforming process with high strength aluminum alloy[J]. Materials Science and Engineering:A,2018,711:650-658.
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