Despite the industrial significance of grain size for enhancing mechanical properties and formability,the in-depth deformation mechanisms at elevated temperature are still unclear.To investigate the functions of grain...Despite the industrial significance of grain size for enhancing mechanical properties and formability,the in-depth deformation mechanisms at elevated temperature are still unclear.To investigate the functions of grain size on hot workability and deformation mechanisms,three groups of Mg-1.2Zn-0.2Y alloy specimens with different grain sizes were hot compressed and then studied by combining constitutive model,processing map and microstructural observations.The results showed that the enhanced hot workability accompanying low deformation activation energy and small instability regime was obtained with refined grain size.During hot deformation,the decreased grain size in Mg1.2Zn-0.2Y alloy mainly improved the plastic deformation homogeneity,especially for the weakened local straining around grain boundaries.As a result,the dynamic recrystallization nucleation and texture development at lower strain level were influenced by the initial grain size.At higher strain magnitude,the growth and coarsening of dynamic recrystallized grains would further release strain localization and improve hot workability,while the texture was less impacted.Further,unlike the primary basal slip and deformation twinning in the specimen with coarse grain at low temperature,non-basal slips of dislocations were initiated with less deformation twins in the specimens with refined grain size.展开更多
由于镁合金凝固温度区间很长,所以容易产生热裂。作为新型的高强度变形镁合金,Mg-Zn-Y(ZW系)合金在半连续铸造过程中极易发生热裂。采用"CRC"(Constrained Rod Casting)铸造热裂试验及冷却曲线热分析方法研究了ZW系中ZW22、Z...由于镁合金凝固温度区间很长,所以容易产生热裂。作为新型的高强度变形镁合金,Mg-Zn-Y(ZW系)合金在半连续铸造过程中极易发生热裂。采用"CRC"(Constrained Rod Casting)铸造热裂试验及冷却曲线热分析方法研究了ZW系中ZW22、ZW42、ZW44、ZW26、ZW62合金的凝固路径,凝固最后阶段剩余液相分数以及锆细化等因素和其热裂倾向的关系。热裂纹位置因子、宽度因子等热裂敏感性因子的表征结果表明,合金的热裂倾向从大到小顺序为:无Zr的ZW62>ZW62>ZW22,ZW42和ZW44>ZW26合金。无Zr的ZW62合金比其他合金具有更大热裂倾向与几方面因素有关:具有最长的凝固温度区间;从枝晶干涉点到凝固终了温度间形成W相,阻碍枝晶间剩余液体的流动性,不利于枝晶间补缩;最后凝固阶段剩余液相最少,且该阶段固相分数随温度降低增长缓慢;粗大组织和发达的枝晶。展开更多
The hot tearing susceptibility of MgZn2.5YxZr0.5 （x=0.5, 1, 2, 4, 6） alloys was evaluated by thermodynamic calculations based on Clyne-Davies model. The microstructure and morphology of hot tearing regions of the al...The hot tearing susceptibility of MgZn2.5YxZr0.5 （x=0.5, 1, 2, 4, 6） alloys was evaluated by thermodynamic calculations based on Clyne-Davies model. The microstructure and morphology of hot tearing regions of the alloys were observed by X-ray diffraction and scanning electron microscopy. The solidification temperature and shrinkage stress during the solidification of MgZn2.5YxZr0.5 alloys in the“T”type hot tearing permanent-mold were acquired with the attached computer. The effect factors of hot tearing susceptibility of MgZn2.5YxZr0.5 alloys, such as the solidification temperature interval, the variation of solid fraction in vulnerable region, the residual liquid fraction in the final stage, the type of the second phase of the alloys were discussed based on the above calculation and observation. The results demonstrated that the hot tearing susceptibility in the investigated alloys was found as follows：MgZn2.5Y2Zr0.5＆gt;MgZn2.5Y0.5Zr0.5＆gt;MgZn2.5Y4Zr0.5＆gt;MgZn2.5Y6Zr0.5＆gt;MgZn2.5Y1Zr0.5. The highest hot tearing susceptibility of MgZn2.5Y2Zr0.5 alloy related to the following reasons： the largest freezing range, the biggest changing of the variation of solid fraction in vulnerable region, the least liquid film in the final stage of solidification, the formation of the second phase which worsens the liquid flow and interdendritic feeding after dendrite coherency.展开更多
Long period stacking ordered（LPSO） structure phases were prepared by conventional solidification method in Mg（94）Zn3YxGd（3-x）（x=3,2,1.5,1,mole fraction） alloys,the microstructures,corrosion and compressive mec...Long period stacking ordered（LPSO） structure phases were prepared by conventional solidification method in Mg（94）Zn3YxGd（3-x）（x=3,2,1.5,1,mole fraction） alloys,the microstructures,corrosion and compressive mechanical properties of which were investigated,separately.The results reveal that the microstructures of the as-cast Mg（94）Zn3YxGd（3-x） alloys,with n（Zn）/n（Y＋Gd）=1：1,consist of α（Mg） phase,Mg3Zn3RE2（W） phase,Mg（12）ZnRE（14H-LPSO） phase and a few bright cube-shaped Mg-Y-Gd phases.The formation and the distribution of LPSO-phase in the alloys can be influenced by the content of Gd.The volume fraction of 14H-LPSO phase increases first and then decreases with the increase of the Gd content.For the electrochemical impedance spectroscopy（EIS） measurement,a R（Q（R（QR））） model was used to fit the test results in 3.5%（mass fraction） NaCl solution at room temperature.The corrosion current densities of all samples are about 10-（-5） A/cm-2.When x（Gd）≤1%,Mg-Zn-Y-（Gd）alloy shows good corrosion resistance,which is better than that of the commercial AZ91 D magnesium alloy.The corrosion rate increases when the Gd content is higher than 1.5%.At room temperature,the compressive properties of Mg-Zn-Y-（Gd） alloys increase remarkably with the increase of the volume fraction of LPSO phase.In addition,the pinning effect of W-phase and dispersive cube-shaped Mg-Y-Gd phase is beneficial to improving the mechanical properties of as-cast Mg（94）Zn3YxGd（3-x） alloy in deformation process.展开更多
基金supported by Chongqing Talent Plan:Leading Talents in Innovation and Entrepreneurship,China(No.CQYC201903051)University Innovation Research Group of Chongqing,China(No.CXQT20023)+4 种基金Qingnian Project of Science and Technology Research Program of Chongqing Municipal Education Commission,China(No.KJQN202001106)China Postdoctoral Science Foundation(No.2021M700556)Natural Science Foundation of Chongqing,China(No.cstc2021jcyj-bsh X0114)Natural Science Foundation of China(Nos.U20A20234,51874062)Chongqing Foundation and Advanced Research Project,China(No.cstc2019jcyj-zdxm X0010)。
基金supported by the National Natural Science Foundation of China(51774124,52074114)Hunan Provincial Natural Science Foundation of China(2019JJ40017,2020JJ5062)+1 种基金Key Technologies R&D in Strategic Emerging Industries and Transformation in High-tech Achievements Program of Hunan Province(2019GK4045)Graduate Training and Innovation Practice Base of Hunan Province.
文摘Despite the industrial significance of grain size for enhancing mechanical properties and formability,the in-depth deformation mechanisms at elevated temperature are still unclear.To investigate the functions of grain size on hot workability and deformation mechanisms,three groups of Mg-1.2Zn-0.2Y alloy specimens with different grain sizes were hot compressed and then studied by combining constitutive model,processing map and microstructural observations.The results showed that the enhanced hot workability accompanying low deformation activation energy and small instability regime was obtained with refined grain size.During hot deformation,the decreased grain size in Mg1.2Zn-0.2Y alloy mainly improved the plastic deformation homogeneity,especially for the weakened local straining around grain boundaries.As a result,the dynamic recrystallization nucleation and texture development at lower strain level were influenced by the initial grain size.At higher strain magnitude,the growth and coarsening of dynamic recrystallized grains would further release strain localization and improve hot workability,while the texture was less impacted.Further,unlike the primary basal slip and deformation twinning in the specimen with coarse grain at low temperature,non-basal slips of dislocations were initiated with less deformation twins in the specimens with refined grain size.
文摘由于镁合金凝固温度区间很长,所以容易产生热裂。作为新型的高强度变形镁合金,Mg-Zn-Y(ZW系)合金在半连续铸造过程中极易发生热裂。采用"CRC"(Constrained Rod Casting)铸造热裂试验及冷却曲线热分析方法研究了ZW系中ZW22、ZW42、ZW44、ZW26、ZW62合金的凝固路径,凝固最后阶段剩余液相分数以及锆细化等因素和其热裂倾向的关系。热裂纹位置因子、宽度因子等热裂敏感性因子的表征结果表明,合金的热裂倾向从大到小顺序为:无Zr的ZW62>ZW62>ZW22,ZW42和ZW44>ZW26合金。无Zr的ZW62合金比其他合金具有更大热裂倾向与几方面因素有关:具有最长的凝固温度区间;从枝晶干涉点到凝固终了温度间形成W相,阻碍枝晶间剩余液体的流动性,不利于枝晶间补缩;最后凝固阶段剩余液相最少,且该阶段固相分数随温度降低增长缓慢;粗大组织和发达的枝晶。
基金Project (2011BAE22B01) supported by the National Key Technologies R&D Program,ChinaProject (2013CB632203) supported by the National Basic Research Program of China
文摘The hot tearing susceptibility of MgZn2.5YxZr0.5 （x=0.5, 1, 2, 4, 6） alloys was evaluated by thermodynamic calculations based on Clyne-Davies model. The microstructure and morphology of hot tearing regions of the alloys were observed by X-ray diffraction and scanning electron microscopy. The solidification temperature and shrinkage stress during the solidification of MgZn2.5YxZr0.5 alloys in the“T”type hot tearing permanent-mold were acquired with the attached computer. The effect factors of hot tearing susceptibility of MgZn2.5YxZr0.5 alloys, such as the solidification temperature interval, the variation of solid fraction in vulnerable region, the residual liquid fraction in the final stage, the type of the second phase of the alloys were discussed based on the above calculation and observation. The results demonstrated that the hot tearing susceptibility in the investigated alloys was found as follows：MgZn2.5Y2Zr0.5＆gt;MgZn2.5Y0.5Zr0.5＆gt;MgZn2.5Y4Zr0.5＆gt;MgZn2.5Y6Zr0.5＆gt;MgZn2.5Y1Zr0.5. The highest hot tearing susceptibility of MgZn2.5Y2Zr0.5 alloy related to the following reasons： the largest freezing range, the biggest changing of the variation of solid fraction in vulnerable region, the least liquid film in the final stage of solidification, the formation of the second phase which worsens the liquid flow and interdendritic feeding after dendrite coherency.
基金Project(51374084)supported by the National Natural Science Foundation of ChinaProject supported by the Power Electronics Science and Education Development Program of Delta Environmental&Educational Foundation,ChinaProject(2010K10-08)supported by the Science and Technology Plan(Industrial Research)of Shaanxi Province,China
文摘Long period stacking ordered（LPSO） structure phases were prepared by conventional solidification method in Mg（94）Zn3YxGd（3-x）（x=3,2,1.5,1,mole fraction） alloys,the microstructures,corrosion and compressive mechanical properties of which were investigated,separately.The results reveal that the microstructures of the as-cast Mg（94）Zn3YxGd（3-x） alloys,with n（Zn）/n（Y＋Gd）=1：1,consist of α（Mg） phase,Mg3Zn3RE2（W） phase,Mg（12）ZnRE（14H-LPSO） phase and a few bright cube-shaped Mg-Y-Gd phases.The formation and the distribution of LPSO-phase in the alloys can be influenced by the content of Gd.The volume fraction of 14H-LPSO phase increases first and then decreases with the increase of the Gd content.For the electrochemical impedance spectroscopy（EIS） measurement,a R（Q（R（QR））） model was used to fit the test results in 3.5%（mass fraction） NaCl solution at room temperature.The corrosion current densities of all samples are about 10-（-5） A/cm-2.When x（Gd）≤1%,Mg-Zn-Y-（Gd）alloy shows good corrosion resistance,which is better than that of the commercial AZ91 D magnesium alloy.The corrosion rate increases when the Gd content is higher than 1.5%.At room temperature,the compressive properties of Mg-Zn-Y-（Gd） alloys increase remarkably with the increase of the volume fraction of LPSO phase.In addition,the pinning effect of W-phase and dispersive cube-shaped Mg-Y-Gd phase is beneficial to improving the mechanical properties of as-cast Mg（94）Zn3YxGd（3-x） alloy in deformation process.
