均匀化处理对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金组织和力学性能的影响
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摘要
对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金铸锭进行均匀化处理,温度为505～525℃,时间为4～24h,并采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和万能材料试验机等检测手段分析均匀化处理前后合金微观组织和力学性能的变化。结果表明:均匀化处理后,原始组织中网状分布共晶化合物转化成晶界处不连续分布的块状LPSO相,离散分布的方块状富稀土相溶解。力学性能测试显示,铸态镁合金的抗拉强度为172.9MPa,伸长率为1.8%,经过均匀化处理后合金的力学性能得到提高,在515℃/16h均匀化制度下,合金室温抗拉强度为212.3MPa,伸长率为3.1%;在200℃下抗拉强度为237.2MPa,伸长率为9.7%,性能达到最佳。断口扫描显示,铸态合金是以撕裂棱与解理台阶为主的解理脆性断裂,均匀化处理后的合金中出现小而浅的韧窝,但仍然是以解理台阶为主的准解理断裂,塑性提高有限,长程有序相可成为裂纹的萌生源。
Homogenization heat treatment on the as-cast Mg-13 Gd-3.5 Y-2 Zn-0.5 Zr magnesium alloy was carried out with the temperature range of 505-525℃ and the time range of 4-24 h. Optical microscope(OM), scanning electron microscope(SEM), X-ray diffractometer(XRD) and universal material experiment machine were used to analysize the changes of microstructure evolution and mechanical property before and after homogenization. The results show that the reticular eutectic compounds in initial grain structure are transformed into discontinuous bulk-shaped LPSO(long-period stacking ordered) phases at the grain boundary and the discrete distribution of the square-shaped rich rare-earth phases dissolved. The mechanical properties test results show that the ultimate tensile strength and the elongation of the cast magnesium alloy are 172.9 MPa and 1.8%, respectively. The mechanical properties of the alloy are improved after homogenization, the ultimate tensile strength of room temperature is 212.3 MPa and the elongation is 3.1% under the homogenization of 515℃/16 h. At the same time, the ultimate tensile strength of high temperature at 200℃ reaches the highest 237.2 MPa and the elongation is 9.7%. The fracture microstructure of as-cast alloy indicates that the fracture is cleavage brittle fracture dominated by tearing edges and cleavage steps, small and shallow dimples occur in the alloy after homogenization treatment, but is still quasi-cleavage fracture dominated by cleavege steps, and limited plasticity is improved. Meanwhile, LPSO phase can be the crack initiation source.
Homogenization heat treatment on the as-cast Mg-13 Gd-3.5 Y-2 Zn-0.5 Zr magnesium alloy was carried out with the temperature range of 505-525℃ and the time range of 4-24 h. Optical microscope(OM), scanning electron microscope(SEM), X-ray diffractometer(XRD) and universal material experiment machine were used to analysize the changes of microstructure evolution and mechanical property before and after homogenization. The results show that the reticular eutectic compounds in initial grain structure are transformed into discontinuous bulk-shaped LPSO(long-period stacking ordered) phases at the grain boundary and the discrete distribution of the square-shaped rich rare-earth phases dissolved. The mechanical properties test results show that the ultimate tensile strength and the elongation of the cast magnesium alloy are 172.9 MPa and 1.8%, respectively. The mechanical properties of the alloy are improved after homogenization, the ultimate tensile strength of room temperature is 212.3 MPa and the elongation is 3.1% under the homogenization of 515℃/16 h. At the same time, the ultimate tensile strength of high temperature at 200℃ reaches the highest 237.2 MPa and the elongation is 9.7%. The fracture microstructure of as-cast alloy indicates that the fracture is cleavage brittle fracture dominated by tearing edges and cleavage steps, small and shallow dimples occur in the alloy after homogenization treatment, but is still quasi-cleavage fracture dominated by cleavege steps, and limited plasticity is improved. Meanwhile, LPSO phase can be the crack initiation source.
引文
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[2] 胡耀波,赵冲,吴福洲,等.Mg-Zn-xCu-Ce镁合金铸态组织与力学性能[J].材料工程,2012(5):1-5.HU Y B,ZHAO C,WU F Z,et al.Microstructure and mechanical properties of as-cast Mg-Zn-xCu-Ce alloys[J].Journal of Materi-als Engineering,2012(5):1-5.
[3] ZHANG Z Z,YAN Z M,DU Y,et al.Hot deformation behavior of homogenized Mg-13.5Gd-3.2Y-2.3Zn-0.5Zr alloy via hot compr-ession tests[J].Materials,2018,11(11):2282.
[4] ZHANG G S,ZHANG Z M,DU Y,et al.Effect of isothermal repetitive upsetting extrusion on the microstructure of Mg-12.0Gd-4.5Y-2.0Y-0.4Zr alloy[J].Materials,2018,11(11):2092.
[5] 刘军,张金玲,渠治波,等.稀土Gd对AZ31镁合金耐蚀性能的影响[J].材料工程,2018,46(6):73-79.LIU J,ZHANG J L,QU Z B,et al.Effect of rare earth Gd on corrosion resistance of AZ31 magnesium alloy[J].Journal of Materials Engineering,2018,46(6):73-79.
[6] 郭旭涛,李培杰,熊玉华,等.稀土在铝、镁合金中的应用[J].材料工程,2004(8):60-64.GUO X T,LI P J,XIONG Y H,et al.Application of rare earth in aluminum and magnesium alloys[J].Journal of Materials Engine-ering,2004(8):60-64.
[7] 刘鹏,江海涛,段晓鸽,等.稀土元素Y和Ce对热轧Mg-1.5Zn镁合金组织和室温成形性能的影响[J].材料工程,2014(12):1-10.LIU P,JIANG H T,DUAN X G,et al.Effects of yttrium(Y) and cerium(Ce) on microstructure and stretch formability of hot rolled Mg-1.5Zn magnesium sheet at room temperature[J].Journal of Materials Engineering,2014(12):1-10.
[8] 任国成,赵国群.AZ31镁合金等通道转角挤压应变累积均匀性分析及组织性能研究[J].材料工程,2013(10):13-19.REN G C,ZHAO G Q.Homogeneous deformation analysis and microstructure properties study of AZ31 magnesium alloy in multi-pass equal channel angular pressing[J].Journal of Mater-ials Engineering,2013(10):13-19.
[9] KAWAMURA Y,HAYASHI K,INOUE A,et al.Rapidly solidi-fied powder metallurgy Mg97Zn1Y2 alloys with excellent tensile yield strength above 600MPa[J].Materials Transactions,2001,42(7):1172-1176.
[10] 张代东,郝晓伟,房大庆,等.热处理对挤压态Mg-9Sn-1.5Y-0.4Zr镁合金显微组织与力学性能的影响[J].稀有金属材料与工程,2016,45(9):2208-2213.ZHANG D D,HAO X W,FANG D Q,et al.Effects of heat treatment on microstructure and mechanical properties of as-extruded Mg-9Sn-1.5Y-0.4Zr magnesium alloy[J].Rare Metal Materials and Engineering,2016,45(9):2208-2213.
[11] WEN K,XIONG B Q,ZHANG Y G,et al.Microstructure evo-lution of a high zinc containing Al-Zn-Mg-Cu alloy during hom-ogenization[J].Rare Metal Materials and Engineering,2017,46(4):928-934.
[12] 张国栋,李兴刚,马鸣龙,等.Mg-7.68Gd-4.88Y-1.32Nd-0.63Al-0.05Zr镁合金的均匀化热处理研究[J].稀土学报,2014,32(5):445-450.ZHANG G D,LI X G,MA M L,et al.Homogenization heat treatment of Mg-7.68Gd-4.88Y-1.32Nd-0.63Al-0.05Zr alloy[J].Journal of Rare Earths,2014,32(5):445-450.
[13] LI M,ZHANG K,DU X G,et al.The effect of homogenization on microstructures and mechanical properties of Mg-7Gd-3Y-1Nd-xZn-0.5Zr(x=0.5,1 and 2wt.%) alloys[J].Materials Characterization,2015,109:66-72.
[14] 田治坤.大型高强耐热镁合金构件的热处理工艺研究[D].太原:中北大学,2016.TIAN Z K.Study on heat treatment process of large high-strength and heat-resistant deforming magnesium alloys component[D].Taiyuan:North University of China,2016.
[15] WU Y J,ZENG X Q,LIN D L,et al.The microstructure evolution with lamellar 14H-type LPSO structure in an Mg96.5Gd2.5Zn1 alloy during solid solution heat treatment at 773K[J].Journal of Alloys and Compounds,2009,477(1/2):193-197.
[16] WU Y J,LIN D L,ZENG X Q,et al.Formation of a lamellar 14H-type long period stacking ordered structure in an as-cast Mg-Gd-Zn-Zr alloy[J].Journal of Materials Science,2009,44(6):1607-1612.
[17] 张士林,任颂赞.简明铝合金手册[M].上海:上海科学技术文献出版社,2006.ZHANG S L,REN S Z.Simple aluminum alloy manual[M].Shanghai:Shanghai Scientific & Technical Publishers,2006.
[18] ZHAO Q L,ZHANG H D,ZHANG X X,et al.Enhanced elevated-temperature mechanical properties of Al-Mn-Mg cont-aining TiC nano-particles by pre-strain and concurrent precip-itation[J].Materials Science and Engineering:A,2018,718(7):305-310.