固溶后的晶粒结构对ZK60镁合金挤压型材力学性能的影响
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摘要
对ZK60镁合金挤压型材在420℃进行不同时间(1、4和8 h)的固溶处理,运用光学显微镜(OM)、X射线衍射仪(XRD)和SEM扫描电镜对原始挤压态及固溶处理后合金的力学性能及拉伸过程中的变形机制进行了研究。结果表明:合金强度随固溶时间的增加不断下降,塑性随固溶时间的增加为先增加后减少,固溶处理4 h时塑性最好,可达28%,且其强度为247 MPa。挤压态及固溶1 h处理后的晶粒结构主要以细晶为主,在拉伸变形过程中位错滑移占主导。固溶处理4 h后的晶粒结构呈现双模态结构,即细晶和粗晶的双模态晶粒结构,在拉伸变形过程中,变形主要由细晶的位错滑移与粗晶的孪生共同主导。固溶处理8 h后的晶粒结构主要以粗晶为主,在拉伸变形过程中孪生变形占主导。SEM断口观察表明,挤压态、固溶处理1、4 h后为韧性断裂,而固溶处理8 h为脆性断裂。
ZK60 alloy extruded profiles was solid solution treated at 420 ℃ for 1,4 and 8 h,respectively. And the mechanical properties and deformation mechanism in the process of tensile test were investigated by means of optical microscope( OM),X-ray diffraction( XRD)and scanning electron microscopy. The results indicate that the strength of the alloy decreases gradually with the solid solution time increasing,whereas the ductility increases first and then decreases,and the ductility is the best when solid solution treated for 4 h,and reach up 28%,when the strength is 247 MPa. The grains of the extruded state and solid solution treatment for 1 h are mainly fine grains,and the deformation mechanics in tensile test is mainly dominated by dislocation sliping. After solid solution treatment for 4 h,the grain structure becomes bimodal: which is consist of fine grains and coarse grains,and the deformation mechanics in tensile test is dominated by dislocation sliping in fine grains and twinning in coarse grains. The grains of the alloy solid solution treated for 8 h are mainly coarse grains,and the deformation in tension is mainly dominated by twinning. The fracture surface observation of SEM shows that the fracture of extruded and solution treated for 1,4 h alloy are ductile fracture,while that of the alloy solution treated for 8 h is brittle fracture.
ZK60 alloy extruded profiles was solid solution treated at 420 ℃ for 1,4 and 8 h,respectively. And the mechanical properties and deformation mechanism in the process of tensile test were investigated by means of optical microscope( OM),X-ray diffraction( XRD)and scanning electron microscopy. The results indicate that the strength of the alloy decreases gradually with the solid solution time increasing,whereas the ductility increases first and then decreases,and the ductility is the best when solid solution treated for 4 h,and reach up 28%,when the strength is 247 MPa. The grains of the extruded state and solid solution treatment for 1 h are mainly fine grains,and the deformation mechanics in tensile test is mainly dominated by dislocation sliping. After solid solution treatment for 4 h,the grain structure becomes bimodal: which is consist of fine grains and coarse grains,and the deformation mechanics in tensile test is dominated by dislocation sliping in fine grains and twinning in coarse grains. The grains of the alloy solid solution treated for 8 h are mainly coarse grains,and the deformation in tension is mainly dominated by twinning. The fracture surface observation of SEM shows that the fracture of extruded and solution treated for 1,4 h alloy are ductile fracture,while that of the alloy solution treated for 8 h is brittle fracture.
引文
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[2]李金柱,郑开宏,王顺成,等.大尺寸ZK60镁合金挤压型材的组织与力学性能[J].热加工工艺,2014(5):20-23.Li Jinzhu,Zheng Kaihong,Wang Shuncheng,et al.Microstructure and mechanical properties of large ZK60 magnesium alloy extruded profiles[J].Hot Working Technology,2014(5):20-23.
[3]Chen Xianhua,Liu Lizi,Pan Fushen.Strength improvement in ZK60magnesium alloy induced by pre-deformation and heat treatment[J].Journal of Wuhan University of Technology(Materials Science Edition),2016,31(2):393-398.
[4]段翠芳,常万军.ZK60镁合金ACPP挤压棒材组织演变及其时效析出强化[J].金属热处理,2014,39(8):49-52.Duan Cuifang,Chang Wanjun.Microstructure evolution of extrusion ZK60 magnesium alloy bar by ACPP and its precipitation strengthening[J].Heat Treatment of Metals,2014,39(8):49-52.
[5]何运斌,潘清林,覃银江,等.热处理工艺对变形ZK60镁合金组织与性能的影响[J].金属热处理,2011,36(1):52-56.He Yunbin,Pan Qinglin,Tan Yinjiang,et al.Effect of heat treatment on microstructure and mechanical properties of wrought ZK60magnesium alloy[J].Heat Treatment of Metals,2011,36(1):52-56.
[6]张晓芳,李保成,李兆智.T5热处理对挤压态ZK60镁合金组织性能的影响[J].有色金属加工,2008,37(4):28-30.Zhang Xiaofang,Li Baocheng,Li Zhaozhi.Influence of T5 aging treatment on microstructure and mechanical properties of extruded ZK60alloy[J].Nonferrous Metals Processing,2008,37(4):28-30.
[7]陈水先,张辉,严琦琦,等.热处理对挤压镁合金ZK60拉伸变形与断裂行为的影响[J].金属热处理,2008,33(6):85-88.Chen Shuixian,Zhang Hui,Yan Qiqi,et al.Effect of heat treatment on tensile deformation and fracture of as-extruded ZK60 magnesium alloy[J].Heat Treatment of Metals,2008,33(6):85-88.
[8]王渠东,林金保,彭立明,等.往复挤压变形对ZK60镁合金力学性能的影响[J].金属学报,2008,44(1):55-58.Wang Qudong,Lin Jinbao,Peng Liming,et al.Influence of cyclic extrusion and compression on the mechanical property of Mg alloy ZK60[J].Acta Metallurgica Sinica,2008,44(1):55-58.
[9]何运斌,潘清林,刘晓艳,等.ECAP法制备细晶ZK60镁合金的微观组织与力学性能[J].材料工程,2011(6):32-38.He Yunbin,Pan Qinglin,Liu Xiaoyan,et al.Microstructure and mechanical properties of ZK60 magnesium alloy produced by equal channel angular pressing[J].Journal of Materials Engineering,2011(6):32-38.
[10]谷祖威,孙春燕.晶粒尺寸对汽车用AZ31B镁合金板材力学性能的影响[J].铸造技术,2013(11):1482-1484.Gu Zuwei,Sun Chunyan.Effects of grain size on mechanical properties of automotive AZ31 Mg-alloy[J].Foundry Technology,2013(11):1482-1484.
[11]Wang Huiyuan,Xue Ensong,Xiao Wei,et al.Influence of grain size on deformation mechanisms in rolled Mg-3Al-3Sn alloy at room temperature[J].Materials Science and Engineering A,2011,528(29):8790-8794.
[12]万响亮,许德明,李光强.晶粒细化对301LN奥氏体不锈钢形变机制和力学性能的影响[C]//第十届中国钢铁年会论文集.中国金属学会,2005:284-289.
[13]Koch C C,Morris D G,Lu K,et al.Ductility of nanostructured materials[J].Mrs Bulletin,1999,24(2):54-58.
[14]Wang Y M,Chen M W,Zhou F H,et al.High tensile ductility in a nanostructured metal[J].Nature,2002,419(6910):912-915.
[15]Tellkamp V L,Lavernia E J,Melmed A.Mechanical behavior and microstructure of a thermally stable bulk nanostructured Al alloy[J].Metallurgical and Materials Transactions A,2001,32(9):2335-2343.
[16]Yi Yang,Xuyue Yang,Zhenyu Xiao,et al.Annealing behavior of a cast Mg-Gd-Y-Zr alloy with necklace fine grains developed under hot deformation[J].Materials Science and Engineering A,2017,688:280-288.
[17]Zhang Zhirou,Yang Xuyue,Xiao Zhenyu,et al.Dynamic recrystallization behaviors of a Mg-4Y-2Nd-0.2Zn-0.5Zr alloy and the resultant mechanical properties after hot compression[J].Materials and Design,2016,97:25-32.
[18]朱林利,吕坚.双模态晶粒尺寸分布纳米结构金属铜的力学性能研究[C]//第十五届中国科协年会第7分会场:先进能源开发装置中的关键力学问题研讨会论文集.中国科学技术协会,2013:15-21.
[19]Oskooie M S,Asgharzadeh H,Kim H S.Microstructure,plastic deformation and strengthening mechanisms of an Al-Mg-Si alloy with a bimodal grain structure[J].Journal of Alloys and Compounds,2015,632:540-548.
[20]Ladani L,Nelson S.Transition of crack propagation path under varied levels of load in bimodal grain size Al-Mg alloy[J].Journal of Engineering Materials and Technology,2011,133(4):041017.
[21]Lee Z,Radmilovic V,Ahn B,et al.Tensile deformation and fracture mechanism of bulk bimodal ultrafine-grained Al-Mg alloy[J].Metallurgical and Materials Transactions A,2010,41(4):795-801.
[22]苏燕铃.孪生在镁合金塑性变形中的作用[D].南京:南京理工大学,2007.
[23]王玉臻,毛泽宁,赵永好.EBSD半原位研究双模晶粒分布铜的变形机理[J].材料科学与工程学报,2015,33(3):343-351.Wang Yuzhen,Mao Zening,Zhao Yonghao.In-situ EBSD study of deformation mechanism in bimodal Cu[J].Journal of Material Science and Engineering,2015,33(3):343-351.
[24]韩松,曾嵩,嵇文清,等.晶粒尺寸、变形温度和应变率对Mg-12Gd-3Y-0.5Zr合金力学性能的影响[J].材料导报,2012,26(12):36-38.Han Song,Zeng Song,Ji Wenqing,et al.Effect of grain size,temperature and strain rate on deformation twin of Mg-12Gd-3Y-0.5Zr alloy[J].Materials Review,2012,26(12):36-38.
[25]Yoo M H.Slip,twinning,and fracture in hexagonal close-packed metals[J].Metallurgical Transactions A,1981,12(3):409-418.