AZ61镁合金降温多向压缩中的动态析出及其对晶粒细化和力学性能的影响
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摘要
对AZ61镁合金进行降温多向压缩变形,利用OM,SEM/EBSD及TEM技术对其晶粒细化和析出相变化进行了观察和分析。结果表明:在623~483 K温度范围内降温多向压缩时AZ61镁合金晶粒急剧细化,低角晶界通过吸收位错转变成高角晶界,而降温变形会明显抑制晶粒长大和晶界高角化,5道次变形后还存在大量中低角晶界,平均晶粒尺寸约为0.8μm。变形初期析出的第二相尺寸较大,随着变形道次的增加,第二相细化的同时数量明显增多。降温变形可促进动态析出,使得析出相分布更加细小、弥散。动态析出使得AZ61相对AZ31镁合金具有更高的硬度。AZ61镁合金经降温变形后强度和延性得到同步提升,尤其是5道次变形后伸长率显著提高,这是细小第二相在中低角晶界上动态析出造成的。
Dynamic precipitation and its effect on grain refinement and mechanical properties of AZ61 Mg alloy during multi-directional forging in temperature range from 623 K to 483 K were investigated by OM, SEM/EBSD and TEM techniques. Dynamic precipitation of Mg17 Al12 phase does happen at the early stage of multi-directional forging and grain size is significantly refined to 0.8 μm after five passes deformation. The initial size of precipitates is relatively big, and then precipitates become dispersed and are refined to nanometer scale. The nanometer dispersed precipitation retards the dislocation movement, along with the temperature decreasing, resulting in the high density of dislocations and low medium angle grain boundaries inside the grain. The strength and ductility of AZ61 Mg alloy are simultaneously improved after multi-directional forging under decreasing temperature. The dramatic improvement of ductility is found after the whole five passes deformation finished, which can be attributed to the dynamic precipitation occurring on the low or medium angle grain boundary.
Dynamic precipitation and its effect on grain refinement and mechanical properties of AZ61 Mg alloy during multi-directional forging in temperature range from 623 K to 483 K were investigated by OM, SEM/EBSD and TEM techniques. Dynamic precipitation of Mg17 Al12 phase does happen at the early stage of multi-directional forging and grain size is significantly refined to 0.8 μm after five passes deformation. The initial size of precipitates is relatively big, and then precipitates become dispersed and are refined to nanometer scale. The nanometer dispersed precipitation retards the dislocation movement, along with the temperature decreasing, resulting in the high density of dislocations and low medium angle grain boundaries inside the grain. The strength and ductility of AZ61 Mg alloy are simultaneously improved after multi-directional forging under decreasing temperature. The dramatic improvement of ductility is found after the whole five passes deformation finished, which can be attributed to the dynamic precipitation occurring on the low or medium angle grain boundary.
引文
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[15]MIURA H,YANG X,SAKAI T.Evolution of ultra-fine grains in AZ31 and AZ61 Mg alloys during multi-directional forging and their properties[J].Mater Trans,2008,49(5):1015-1020.
[16]YU H,PARK S H,YOU B S.Development of extraoridinary high-strength Mg-8Al-0.5Zn alloy via a low temperature and slow speed extrusion[J].Mater Sci Eng A,2014,610:445-449.
[17]YANG X Y,MIURA H,SAKAI T.Dynamic evolution of new grains in magnesium alloy AZ31 during hot deformation[J].Mater Trans,2003,44(1):197-203.
[18]杨续跃,姜育培.镁合金热变形下变形带的形貌和晶体学特征[J].金属学报,2010,46(4):451-457.YANG Xu-yue,JIANG Yu-pei.Morphology and crystallographic characteristics of deformation bands in Mg alloy under hot deformation[J].Acta Metall Sin,2010,46(4):451-457.
[19]CLARK J B.Age hardening in Mg-9wt.%Al alloy[J].Acta Metall,1968,16(2):141-152.
[20]MATHIS K,GUBICZA J,NAM N H.Microstructure and mechanical behavior of AZ91 Mg alloy processed by equal channel angular pressing[J].J Alloys Compd,2005,394:194-199.
[21]CACERES C H,ROVERA D M.Solid solution strengthening in concentrated Mg-Al alloys[J].J Light Met,2001,1(3):151-156.
[22]HUTCHINSON C R,NIE J F,GORSSE S.Modeling the precipitation processes and strengthening mechanisms in a Mg-Al-(Zn)AZ91 alloy[J].Metall Mater Trans A,2004,36(8):2093-2015.
[23]YE Y X,YANG X Y,LIU C Z,SHEN Y Z,ZHANG X K,SAKAI T.Enhancement of strength and ductility of Cu-Sn-Zn alloy by iron addition[J].Mater Sci Eng A,2014,612:246-252.
[24]YANG Qiang,BU Fan-qiang,QIU Xin,LI Yang-de,LI Wei-rong,SUN Wei,LIU Xiao-juan,MENG Jiang.Strengthening effect of nano-scale precipitates in a die-cast Mg-4Al-5.6Sm-0.3Mn alloy[J].J Alloys Compd,2016,665:240-250.
[2]THIRUMURUGAN M,KUMARAN S.Extrusion and precipitation hardening behavior of AZ91 magnesium alloy[J].The Chinese Journal of Nonferrous Metals,2013,23(6):1595-1601.
[3]余琨,黎文献,王日初,马正青.变形镁合金的研究,开发及应用[J].中国有色金属学报,2003,13(2):277-288.YU Kun,LI Wen-xian,WANG Ru-chu,MA Zheng-qing.Research,development and application of wrought magnesium alloys[J].The Chinese Journal of Nonferrous Metals,2003,13(2):277-288.
[4]张笃秀,李祎,叶友雄,沈阳志,杨续跃.微量Fe对冷轧超细晶Cu-30Zn-0.15Fe合金等温退火组织演化的影响[J].金属学报,2016,52(3):369-377.ZHANG Du-xiu,LI Yi,YE You-xiong,XHEN Yang-zhi,YANG Xu-yue.Effect of minor Fe addition on microstructure evolution of ultrafine grained cold rolling Cu-30Zn-0.15Fe alloy subjected to isothermal annealing[J].Acta Metall Sin,2016,52(3):369-377.
[5]MILITZER M,SUN W P,JONAS J J.Modelling the effect of deformation-induced vacancies on segregation and precipitation[J].Acta Metall,1994,42(1):133-141.
[6]ZHAO S T,MENG C L,MAO F X,HU W,GOTTSTEIN G.Influence of severe plastic deformation on dynamic strain aging of untrafine grained Al-Mg alloys[J].Acta Mater,2014,76(2):54-67.
[7]刘六法,丁汉林,丁文江.AZ91镁合金挤压过程中β相的动态析出及其对组织和拉伸性能的影响[J].稀有金属材料与工程,2009,38(1):104-109.LIU Liu-fa,DING Han-ling,DING Wen-jiang.Dynamic precipitation ofβphase during extrusion process and its effects on the microstructures and tensile properties of AZ91magnesium alloy[J].Rare Metal Materials and Engineering,2009,38(1):104-109.
[8]王红霞,周康康,梁伟,龚家林,曹晓卿,赵兴国.Mg15Al镁合金ECAP变形过程中β相的碎化机理及动态析出行为[J].中国有色金属学报,2011,21(9):1794-1800.WANG Hong-xia,ZHOU Kang-kang,LIANG Wei,GONG Jia-lin,CAO Xiao-qing,ZHAO Xing-guo.Fragmentation mechanism and dynamic precipitation behavior ofβphase in Mg15Al magnesium alloy during ECAP[J].The Chinese Journal of Nonferrous Metals,2011,21(9):1794-1800.
[9]GUO F,ZHANG D F,YANG X S,JIANG L Y,PAN F S.Strain-induced precipitation of Mg17Al12 phase in Mg-8Al alloys sheets rolled at 748 K[J].Mater Sci Eng A,2015,636:516-521.
[10]杨续跃,孙欢,吴新星,马继军,秦佳,霍庆欢.AZ21镁合金降温多向压缩过程中的组织和微观织构演化[J].金属学报,2012,48(1):129-134.YANG Xu-yue,SUN Huan,WU Xin-xing,MA Ji-jun,QIN Jia,HUO Qing-huan.Evolutions of microstructure and microtexture in AZ21 Mg alloy during multi-directional forging under decreasing temperature conditions[J].Acta Metall Sin,2012,48(1):129-134.
[11]YANG X Y,SUN Z Y,XING J,HIROMI M,TAKU S.Grain size and texture changes of magnesium alloy AZ31 during multi-directional forging[J].The Chinese Journal of Nonferrous Metals,2008,18(2):200-204.
[12]MIURA H,YU G,YANG X.Multi-directional forging of AZ61Mg alloy under decreasing temperature conditions and improvement of its mechanical properties[J].Mater Sci Eng A,2011,528:6981-6992.
[13]JIANG M G,YAN H,CHEN R S.Twinning,recrystallization and texture development during multi-directional impact forging in an AZ61 Mg alloy[J].J Alloys Compd,2015,650:399-409.
[14]SOMJEET B,SATYAM S.Evolution of sub-micron grain size and weak texture in magnesium alloy Mg-3Al-0.4Mn by a modified multi-axial forging process[J].Scr Mater,2012,66(2):89-92.
[15]MIURA H,YANG X,SAKAI T.Evolution of ultra-fine grains in AZ31 and AZ61 Mg alloys during multi-directional forging and their properties[J].Mater Trans,2008,49(5):1015-1020.
[16]YU H,PARK S H,YOU B S.Development of extraoridinary high-strength Mg-8Al-0.5Zn alloy via a low temperature and slow speed extrusion[J].Mater Sci Eng A,2014,610:445-449.
[17]YANG X Y,MIURA H,SAKAI T.Dynamic evolution of new grains in magnesium alloy AZ31 during hot deformation[J].Mater Trans,2003,44(1):197-203.
[18]杨续跃,姜育培.镁合金热变形下变形带的形貌和晶体学特征[J].金属学报,2010,46(4):451-457.YANG Xu-yue,JIANG Yu-pei.Morphology and crystallographic characteristics of deformation bands in Mg alloy under hot deformation[J].Acta Metall Sin,2010,46(4):451-457.
[19]CLARK J B.Age hardening in Mg-9wt.%Al alloy[J].Acta Metall,1968,16(2):141-152.
[20]MATHIS K,GUBICZA J,NAM N H.Microstructure and mechanical behavior of AZ91 Mg alloy processed by equal channel angular pressing[J].J Alloys Compd,2005,394:194-199.
[21]CACERES C H,ROVERA D M.Solid solution strengthening in concentrated Mg-Al alloys[J].J Light Met,2001,1(3):151-156.
[22]HUTCHINSON C R,NIE J F,GORSSE S.Modeling the precipitation processes and strengthening mechanisms in a Mg-Al-(Zn)AZ91 alloy[J].Metall Mater Trans A,2004,36(8):2093-2015.
[23]YE Y X,YANG X Y,LIU C Z,SHEN Y Z,ZHANG X K,SAKAI T.Enhancement of strength and ductility of Cu-Sn-Zn alloy by iron addition[J].Mater Sci Eng A,2014,612:246-252.
[24]YANG Qiang,BU Fan-qiang,QIU Xin,LI Yang-de,LI Wei-rong,SUN Wei,LIU Xiao-juan,MENG Jiang.Strengthening effect of nano-scale precipitates in a die-cast Mg-4Al-5.6Sm-0.3Mn alloy[J].J Alloys Compd,2016,665:240-250.