均匀化处理对Mg-Gd-Y-Zn-Zr合金微观组织和力学性能的影响
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摘要
采用SEM、DSC、OM和室温拉伸试验等方法研究了Mg-Gd-Y-Zn-Zr合金均匀化处理过程中长周期堆垛有序(LPSO)相演变及其对力学性能的影响。结果表明:合金铸态下的第二相含量从中心、R/2到边部依次减少,分别是11.72%、9.04%和6.71%。均匀化之后,LPSO相主要呈块状分布在晶界,并以层状向α-Mg晶粒内部延伸。LPSO相含量与LPSO相溶解温度(527.2℃)有关,520℃均匀化处理后LPSO相析出的更充分、含量最大,并且延长均匀化时间有利于LPSO相的析出。OM分析显示,LPSO相对晶界迁移有钉扎作用,使得510℃时晶粒没有发生明显的长大,而在530℃时发生剧烈长大,520℃×12 h均匀化时组织为晶粒尺寸90.79μm的细小等轴晶。拉伸试验表明,合金抗拉强度和伸长率与LPSO相析出量呈正相关,520℃×12 h时LPSO相含量最多,对应的抗拉强度和伸长率最大,分别是244.64 MPa和7.68%。
SEM,DSC,OM and room temperature tensile test were used to research the evolution of long-period stacking ordered(LPSO)phase of Mg-Gd-Y-Zn-Zr alloy and its effect on mechanical properties during homogenization process.The results show that the content of second phase in the as-cast alloy decreases from 11.72% at the center to 9.04% at the R/2,then to 6.71% at the edge of the ingot.After homogenization,the LPSO phase is mainly distributed at the grain boundary in bulky and extends inside α-Mg grains in layers.The LPSO phase content is related to the LPSO phase dissolution temperature(527.2 ℃).From SEM observation,the LPSO phase precipitates more fully and has the largest content in the homogenization treatment at 520 ℃,and prolonging the homogenization time is favorable for LPSO phase dissolution.OM examination shows that LPSO phase has pinning effect on the grain boundary migration,so that the grains will not grow significantly at 510 ℃,but they grow sharply at 530 ℃,and the 520 ℃ × 12 h homogenized microstructure is composed of fine equiaxed grains average sized 90.79 μm.Tensile tests show that the tensile strength and elongation of the alloy are positively correlated with the amount of LPSO phase precipitated.At 520 ℃ × 12 h,the LPSO phase content is the maximum,and the corresponding tensile strength and elongation are the best ones,being 244.64 MPa and 7.68%.
SEM,DSC,OM and room temperature tensile test were used to research the evolution of long-period stacking ordered(LPSO)phase of Mg-Gd-Y-Zn-Zr alloy and its effect on mechanical properties during homogenization process.The results show that the content of second phase in the as-cast alloy decreases from 11.72% at the center to 9.04% at the R/2,then to 6.71% at the edge of the ingot.After homogenization,the LPSO phase is mainly distributed at the grain boundary in bulky and extends inside α-Mg grains in layers.The LPSO phase content is related to the LPSO phase dissolution temperature(527.2 ℃).From SEM observation,the LPSO phase precipitates more fully and has the largest content in the homogenization treatment at 520 ℃,and prolonging the homogenization time is favorable for LPSO phase dissolution.OM examination shows that LPSO phase has pinning effect on the grain boundary migration,so that the grains will not grow significantly at 510 ℃,but they grow sharply at 530 ℃,and the 520 ℃ × 12 h homogenized microstructure is composed of fine equiaxed grains average sized 90.79 μm.Tensile tests show that the tensile strength and elongation of the alloy are positively correlated with the amount of LPSO phase precipitated.At 520 ℃ × 12 h,the LPSO phase content is the maximum,and the corresponding tensile strength and elongation are the best ones,being 244.64 MPa and 7.68%.
引文
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[29]Gao Y,Wang Q,Gu J,et al.Behavior of Mg-15Gd-5Y-0.5Zr alloy during solution heat treatment from 500 to 540℃[J].Materials Science and Engineering A,2007,459(1):117-123.
[30]Hagihara K,Kinoshita A,Sugino Y,et al.Effect of long-period stacking ordered phase on mechanical properties of Mg97Zn1Y2extruded alloy[J].Acta Materialia,2010,58(19):6282-6293.
[2]Huo Q,Yang X,Wang J,et al.Mechanical behavior and deformation mechanisms of AZ31 Mg alloy at liquid nitrogen temperature[J].Materials Letters,2013,109:78-82.
[3]Zhou X,Liu C,Gao Y,et al.Microstructure and mechanical properties of extruded Mg-Gd-Y-Zn-Zr alloys filled with intragranular LPSO phases[J].Materials Characterization,2018,135:76-83.
[4]Zheng J,Chen B.Interactions between long-period stacking ordered phase andβ'precipitate in Mg-Gd-Y-Zn-Zr alloy:Atomic-scale insights from HAADF-STEM[J].Materials Letters,2016,176:223-227.
[5]Zhu Y M,Morton A J,Nie J F.The 18R and 14H long-period stacking ordered structures in Mg-Y-Zn alloys[J].Acta Materialia,2010,58(8):2936-2947.
[6]Egusa D,Abe E.The structure of long period stacking/order Mg-ZnRE phases with extended non-stoichiometry ranges[J].Acta Materialia,2012,60(1):166-178.
[7]Homma T,Kunito N,Kamado S.Fabrication of extraordinary highstrength magnesium alloy by hot extrusion[J].Scripta Materialia,2009,61(6):644-647.
[8]Okuda H,Horiuchi T,Yamasaki M,et al.In situ measurements on stability of long-period stacking-ordered structures in Mg85Y9Zn6 alloys during heating examined by multicolor synchrotron radiation small-angle scattering[J].Scripta Materialia,2014,75:66-69.
[9]Leng Z,Zhang J,Zhang M,et al.Microstructure and high mechanical properties of Mg-9RY-4Zn(RY:Y-rich misch metal)alloy with long period stacking ordered phase[J].Materials Science and Engineering A,2012,540:38-45.
[10]Tane M,Nagai Y,Kimizuka H,et al.Elastic properties of an Mg-Zn-Yalloy single crystal with a long-period stacking-ordered structure[J].Acta Materialia,2013,61(17):6338-6351.
[11]Garces G,Morris D G,Mu1oz-Morris M A,et al.Plasticity analysis by synchrotron radiation in a Mg97Y2Zn1alloy with bimodal grain structure and containing LPSO phase[J].Acta Materialia,2015,94:78-86.
[12]Chino Y,Mabuchi M,Hagiwara S,et al.Novel equilibrium two phase Mg alloy with the long-period ordered structure[J].Scripta Materialia,2004,51(7):711-714.
[13]Itoi T,Seimiya T,Kawamura Y,et al.Long period stacking structures observed in Mg97Zn1Y2alloy[J].Scripta Materialia,2004,51(2):107-111.
[14]Matsuda M,Ando S,Nishida M.Dislocation structure in rapidly solidified Mg97Zn1Y2alloy with long period stacking order phase[J].Materials Transactions,2005,46(2):361-364.
[15]Abe E,Kawamura Y,Hayashi K,et al.Long-period ordered structure in a high-strength nanocrystalline Mg-1at%Zn-2at%Y alloy studied by atomic-resolution Z-contrast STEM[J].Acta Materialia,2002,50(15):3845-3857.
[16]Honma T,Ohkubo T,Kamado S,et al.Effect of Zn additions on the age-hardening of Mg-2.0Gd-1.2Y-0.2Zr alloys[J].Acta Materialia,2007,55(12):4137-4150.
[17]Liu K,Wang X,Wen K.Effect of isothermal homogenization on microstructure and mechanical properties of the Mg-5Y-4Gd-0.5Zn-0.4Zr alloy[J].Materials and Design,2013,52:1035-1042.
[18]Chen T,Chen Z,Shao J,et al.Evolution of LPSO phases in a MgZn-Y-Gd-Zr alloy during semi-continuous casting,homogenization and hot extrusion[J].Materials and Design,2018,152:1-9.
[19]Zhu Y M,Morton A J,Nie J F.Growth and transformation mechanisms of 18R and 14H in Mg-Y-Zn alloys[J].Acta Materialia,2012,60(19):6562-6572.
[20]Nie J F,Zhu Y M,Morton A J.On the structure,transformation and deformation of long-period stacking ordered phases in Mg-Y-Zn alloys[J].Metallurgical and Materials Transactions A,2014,45(8):3338-3348.
[21]Yamasaki M,Sasaki M,Nishijima M,et al.Formation of 14H long period stacking ordered structure and profuse stacking faults in Mg-ZnGd alloys during isothermal aging at high temperature[J].Acta Materialia,2007,55(20):6798-6805.
[22]Xu C,Zheng M Y,Wu K,et al.Effect of cooling rate on the microstructure evolution and mechanical properties of homogenized MgGd-Y-Zn-Zr alloy[J].Materials Science and Engineering A,2013,559:364-370.
[23]Li Y X,Zhu G Z,Qiu D,et al.The intrinsic effect of long period stacking ordered phases on mechanical properties in Mg-RE based alloys[J].Journal of Alloys and Compounds,2016,660:252-257.
[24]Xu C,Zheng M Y,Chi Y Q,et al.Microstructure and mechanical properties of the Mg-Gd-Y-Zn-Zr alloy fabricated by semi-continuous casting[J].Materials Science and Engineering A,2012,549:128-135.
[25]Zhang S,Yuan G Y,Lu C,et al.The relationship between(Mg,Zn)3RE phase and 14H-LPSO phase in Mg-Gd-Y-Zn-Zr alloys solidified at different cooling rates[J].Journal of Alloys and Compounds,2011,509(8):3515-3521.
[26]Yu Z,Xu C,Meng J,et al.Microstructure evolution and mechanical properties of as-extruded Mg-Gd-Y-Zr alloy with Zn and Nd additions[J].Materials Science and Engineering A,2018,713:234-243.
[27]Li J P,Yang Z,Liu T,et al.Microstructures of extruded Mg-12Gd-1Zn-0.5Zr and Mg-12Gd-4Y-1Zn-0.5Zr alloys[J].Scripta Materialia,2007,56(2):137-140.
[28]Xue Z Y,Ren Y J,Luo W B,et al.Microstructure evolution and mechanical properties of a large-sized ingot of Mg-9Gd-3Y-1.5Zn-0.5Zr(wt%)alloy after a lower-temperature homogenization treatment[J].International Journal of Minerals,Metallurgy and Materials,2017,24(3):271-279.
[29]Gao Y,Wang Q,Gu J,et al.Behavior of Mg-15Gd-5Y-0.5Zr alloy during solution heat treatment from 500 to 540℃[J].Materials Science and Engineering A,2007,459(1):117-123.
[30]Hagihara K,Kinoshita A,Sugino Y,et al.Effect of long-period stacking ordered phase on mechanical properties of Mg97Zn1Y2extruded alloy[J].Acta Materialia,2010,58(19):6282-6293.