Dynamic Recrystallization Behavior of Mg-11Gd-3Y-0.5Nd-Zr Alloy with Two Typical Initial Orientations
-
摘要:
对锻态Mg-11Gd-3Y-0.5Nd-Zr合金进行520 ℃×18 h的退火,再分别沿平行于和垂直于锻造方向取样（0°,90°试样）并沿试样轴向进行高温压缩,研究了不同变形量（25%,50%,70%）高温压缩过程中的动态再结晶行为,分析了塑性变形机制及其对动态再结晶的影响。结果表明：随着变形量增加,0°试样和90°试样的动态再结晶面积分数均逐渐增大；90°试样的动态再结晶面积分数相比0°试样更小,尤其在变形量50%下二者相差最大；0°试样和90°试样的塑性变形机制均为棱柱面滑移；90°试样的无滑移系启动晶粒数量相比0°试样更少,棱柱面滑移施密特因子更接近0.5,小角度晶界密度更大,接近1的晶间变形协调因子占比更大,说明其滑移更容易启动,晶间变形协调能力也更强,变形更分散,更难激活动态再结晶。
Abstract:The forged Mg-11Gd-3Y-0.5Nd-Zr alloy was annealed at 520 ℃ for 18 h. Then the 0° sample and 90° sample were taken parallel to and perpendicular to the forging direction respectively, and hot compression was carried out along the sample axial direction. The dynamic recrystallization behavior of the samples under hot compression with different deformation (25%, 50%, 70%) was studied. The mechanism of plastic deformation and its influence on dynamic recrystallization were analyzed. The results show that the dynamic recrystallization area fraction of the 0° sample and 90° sample increased with the increase of the deformation. The dynamic recrystallization area fraction of 90° sample was smaller than that of 0° sample, especially when the deformation was 50% the difference between those two was largest. The plastic deformation mechanism of 0° sample and 90° sample was prismatic plane slip. The number of initiating grains of the non-slip system of 90° sample was less comparied to that of 0° sample, the Schmidt factor for prismatic plane slip was closer to 0.5, the low angle grain boundary density was larger, and the proportion of intergranular deformation coordination factor close to 1 was larger, indicating that the slip of the 90° sample was easier to start, the intergranular deformation coordination ability was stronger, the deformation was more dispersed, and was more difficult to activate dynamic recrystallization.
-
Keywords:
- magnesium alloy /
- initial orientation /
- hot compression /
- dynamic recrystallization
-
0. 引言
镁合金由于具有比强度高、比刚度高、阻尼性能好等优点,广泛应用于航空航天、交通运输、电子通信等领域[1-4]。然而,镁合金具有塑性低的缺点,限制了其实际应用。为了同步提高镁合金的塑性和强度,研究人员提出向合金中引入一种双峰分布晶粒组织,该组织由拉长的变形晶粒（粗晶）和等轴的动态再结晶晶粒（细晶）构成[5-7],形成该组织结构的关键在于动态再结晶。目前,促进动态再结晶的方法主要包括：控制变形条件,例如提高变形温度、增加变形量、降低应变速率等[8]；调控初始晶粒尺寸和初始取向,当初始晶粒尺寸低于某一临界值时,合金容易发生动态再结晶,当晶粒初始取向有利于位错的滑移和攀移时,合金中的位错密度增加,为动态再结晶提供了驱动力[9-10]。TANG等[11]研究发现,通过调控镁合金挤压棒材中初始晶粒尺寸,可以控制动态再结晶,从而实现变形粗晶粒和再结晶细晶粒比例的调控。AL-SAMMAN等[12]在不同温度和应变速率下对挤压态AZ31镁合金进行单轴压缩试验,发现初始取向会影响合金的变形行为和动态再结晶行为。近年来,相关研究多集中于初始取向对变形温度较低的Mg-Al-Zn等合金的动态再结晶行为的影响,对于高稀土含量Mg-Gd-Y系耐热镁合金方面的研究较少[13-15]。为此,作者分别沿平行于锻造方向和垂直于锻造方向在Mg-11Gd-3Y-0.5Nd-Zr合金上取样,并进行了沿试样轴向的高温压缩试验,研究了其在不同变形量（25%,50%,70%）高温压缩过程中的动态再结晶行为,分析了塑性变形机制及其对动态再结晶的影响,以期为高性能镁合金的组织调控提供参考。
1. 试样制备与试验方法
熔铸原料为纯镁、Mg-30Gd中间合金、Mg-30Y中间合金、Mg-30Nd中间合金和Mg-30Zr中间合金。按照名义成分（质量分数/%）为Mg-11Gd-3Y-0.5Nd-Zr进行配料,在GR2-12型坩埚熔化炉中进行熔炼、精炼后,浇注到预热至200 ℃的铁模中,保护气体为纯度99.9%的氩气,制备得到尺寸为150 mm×100 mm×50 mm的铸锭。在铸锭上电火花线切割出尺寸为50 mm×50 mm×50 mm的试样,在SX3-8-10型箱式电阻炉中进行520 ℃×24 h的固溶处理,水冷。在YW32-315T型伺服液压机上进行锻造,锻造前将试样加热至500 ℃并保温1 h,锻造采用多向锻造和单向锻造相结合的方式,多向锻造18道次后单向锻造至试样厚度约为20 mm,单道次变形量均为10%,道次间保温时间为30 min。在锻造后的试样上分别沿平行于和垂直于单向锻造方向制取尺寸为ϕ10 mm×15 mm的圆柱试样,即圆柱圆面分别垂直于和平行于单向锻造方向,分别记作0°试样和90°试样。将圆柱试样进行520 ℃×18 h退火处理,水冷,在Gleeble 3500型热模拟试验机上进行高温压缩试验,压缩方向平行于试样轴向,试验温度为500 ℃,初始应变速率为0.5 s−1,变形量分别为25%,50%,70%。试样经机械预磨、机械抛光、体积分数为4%硝酸乙醇溶液浸蚀15~25 s后,采用EVO Zeiss MA10型扫描电子显微镜（SEM）观察显微组织；另取样经机械研磨、柠檬酸+体积分数4%硝酸乙醇混合溶液腐蚀后,采用SEM的电子背散射衍射模式（EBSD）分析晶粒取向,并采用HKL Channel 5和MTEX数据分析软件统计动态再结晶面积分数。
2. 试验结果与讨论
2.1 动态再结晶面积分数
图1中FD为锻造方向,TD为横向,可见：在锻造过程中试验合金部分晶界处发生了动态再结晶,晶粒尺寸大小不一,分布不均匀,平均晶粒尺寸为66 μm。
图2中测试面为圆柱圆面,TD1和TD2均属横向,可见：退火后0°试样的平均晶粒尺寸为162 μm,相比锻造后大幅增加,这是因为长时间退火使合金内部发生了再结晶和晶粒长大,形成了由较均匀等轴晶构成的组织；退火后试样中不同区域平均取向差较小,计算得到几何必需位错密度为2.72×1012 m−2,且存在较强的基面织构。
![]()
图 2 退火后0°试样IPF图、KAM图和(0001)极图Figure 2. Inverse polar figure (a) , kernel average misorientation diagram (b) and (0001) polar diagram (c) of 0° sample after annealing图3中晶粒A和C为棱柱面滑移启动晶粒,晶粒B和D为无滑移系启动晶粒。可见：25%变形量下高温压缩后,0°试样大多数晶界处均出现少量动态再结晶晶粒,90°试样只在部分晶界处出现了极少量的动态再结晶晶粒；变形量为25%下高温压缩后试样内部产生较多位错,计算可得0°,90°试样的几何必需位错密度分别为1.91×1013,2.00×1013 m−2,说明载荷方向垂直还是平行于锻造方向对几何位错密度影响不大。通过统计位错集中区域（区域Ⅰ、Ⅱ、Ⅲ、Ⅳ）的几何必需位错密度可知,相比90°试样,0°试样位错集中区域的几何必需位错密度较小,这可能是因为其动态再结晶程度提高。
![]()
图 3 25%变形量下高温压缩后0°和90°试样的IPF图、KAM图Figure 3. Inverse polar figure (a, c) and kernel average misorientation diagram (b, d) of 0° sample and 90° sample after hot compression with deformation of 25%由图4可见：变形量为50%下,0°试样的动态再结晶晶粒数量远远多于90°试样。计算可得0°,90°试样的平均几何必需位错密度分别为1.62×1013,2.00×1013 m−2；与变形量为25%下相比,0°试样的几何必需位错密度下降幅度更大,这是因为此时试样产生了更多的动态再结晶晶粒,消耗了更多位错。统计得到变形量分别为25%,50%,70%下,0°试样的动态再结晶面积分数分别为10.8%,44.2%,89.8%,90°试样的分别为3.7%,24.6%,79.2%；变形量为70%时试样动态再结晶面积分数均较高。在相同变形量下,0°试样的动态再结晶面积分数高于90°试样,其中,变形量50%条件下相差最大。
![]()
图 4 50%变形量下高温压缩后0°和90°试样的IPF图和KAM图Figure 4. Inverse polar figure (a, c) and kernel average misorientation diagram (b, d) of 0° sample and 90° sample after hot compression with deformation of 50%2.2 塑性变形机制及其对再结晶的影响
可以通过晶内取向差轴（IGMA）图判断当前状态下晶粒滑移系的启动情况[16]。由于晶粒较多,仅选取图3中晶粒A、B、C、D进行IGMA分析。由图5可见：变形量为25%下,0°试样A晶粒和90°试样C晶粒的IGMA峰值均集中在〈0001〉轴附近,说明棱柱面滑移启动,塑性变形主要由棱柱面滑移主导和协调,而0°试样B晶粒和90°试样D晶粒的IGMA峰值小于2.0,说明无滑移系启动；0°试样中无滑移系启动的晶粒数量多于90°试样,且无滑移启动晶粒分布更集中。此外,由于变形量25%下0°和90°试样的几何必需位错密度相近,而90°试样中启动滑移晶粒更多,说明该试样中有更多的空间去协调变形,从而更不易形成塞积,储能更小,动态再结晶更不容易发生。
![]()
图 5 50%变形量下高温压缩后0°试样和90°试样中典型晶粒的IGMA图和无滑移系启动晶粒分布Figure 5. In-grain misorientation axes images (a, c) and no slip system initiating grain distribution (b, d) of 0° sample and 90° sample after hot compression with deformation of 50%根据文献[17]可知,施密特因子越接近0.5,晶粒滑移越易启动。由图6可见：退火后90°试样的棱柱面滑移平均施密特因子为0.4,而0°试样的仅为0.13,说明初始晶粒取向对高温压缩变形过程中滑移启动难易程度的影响非常大；变形量为25%下,0°和90°试样的平均施密特因子分别为0.20,0.33,与退火后的差异减小,其中90°试样平均施密特因子更接近0.5,因此棱柱面滑移更容易,在变形量为25%~50%范围内柱面滑移始终占主导地位,变形更分散,与0°试样的再结晶面积分数差异性持续增大；而变形量为50%下,0°和90°试样的平均施密特因子分别为0.23,0.28,两者近乎相同,说明变形量增加,0°和90°试样的棱柱面滑移平均施密特因子差异减小。
![]()
图 6 不同变形量下高温压缩后0°试样和90°试样的棱柱面滑移施密特因子图Figure 6. Schmid factor figure for prismatic slip of 0° sample and 90° sample after hot compression with different deformations位错滑移的活跃程度还可以通过小角度（2°~4°）晶界密度来反映,小角度晶界密度越大,塑性变形时位错滑移越活跃[18]。由图7可见：变形量为25%,50%下,相比0°试样,90°试样的小角度晶界分布更密集。计算可得变形量为25%下,0°,90°试样的小角度晶界密度分别为0.23,0.29 μm−1,变形量为50%下分别为0.14,0.24 μm−1。90°试样的小角度晶界密度更大,说明该试样位错滑移更活跃,动态再结晶更难发生。
![]()
图 7 不同变形量下高温压缩后0°试样和90°试样的小角度晶界分布Figure 7. Low angle grain boundary distribution of 0° sample and 90° sample after hot compression with different deformations滑移传递机制可以协调变形,从而提高材料塑性[19-24]。两个相邻晶粒的滑移方向间的角度以及滑移面法向间的夹角越小,滑移就越容易在相邻晶粒间进行传递,可用公式[21]表示,如下：
(1) 式中：m´为晶间变形协调因子；ψ为两个相邻晶粒的滑移方向间的夹角；k为两个相邻晶粒的滑移面法线间的夹角。
m′越趋近于1,相邻晶粒间越易发生滑移传递,越趋近于0,滑移传递越难发生。由图8可见：变形量为25%下,90°试样中接近1的晶间变形协调因子占比更大,说明该试样内部晶粒间可以更好地协调滑移传递,位错不易塞积,所以动态再结晶程度更小。
![]()
图 8 25%变形量下高温压缩后0°试样和90°试样的晶间变形协调因子分布Figure 8. Intergranular deformation coordination factor of 0° sample and 90° sample after hot compression with deformation of 25%3. 结论
（1）随着沿试样轴向高温压缩变形量增加,Mg-11Gd-3Y-0.5Nd-Zr合金的动态再结晶面积分数逐渐增大。相比之下,90°试样（垂直于锻造方向取样）的动态再结晶面积分数相比0°试样（平行于锻造方向取样）更小,在变形量50%下二者相差最大。
（2）0°和90°试样的塑性变形机制均为棱柱面滑移。相比之下,90°试样的无滑移系启动的晶粒数量更少,棱柱面滑移施密特因子更接近0.5,小角度晶界密度更大,接近1的晶间变形协调因子占比更大,说明其滑移更容易启动,晶间变形协调能力也更强,变形更分散,更难激活动态再结晶。
-
![]()
图 2 退火后0°试样IPF图、KAM图和(0001)极图
Figure 2. Inverse polar figure (a) , kernel average misorientation diagram (b) and (0001) polar diagram (c) of 0° sample after annealing
![]()
图 3 25%变形量下高温压缩后0°和90°试样的IPF图、KAM图
Figure 3. Inverse polar figure (a, c) and kernel average misorientation diagram (b, d) of 0° sample and 90° sample after hot compression with deformation of 25%
![]()
图 4 50%变形量下高温压缩后0°和90°试样的IPF图和KAM图
Figure 4. Inverse polar figure (a, c) and kernel average misorientation diagram (b, d) of 0° sample and 90° sample after hot compression with deformation of 50%
![]()
图 5 50%变形量下高温压缩后0°试样和90°试样中典型晶粒的IGMA图和无滑移系启动晶粒分布
Figure 5. In-grain misorientation axes images (a, c) and no slip system initiating grain distribution (b, d) of 0° sample and 90° sample after hot compression with deformation of 50%
![]()
图 6 不同变形量下高温压缩后0°试样和90°试样的棱柱面滑移施密特因子图
Figure 6. Schmid factor figure for prismatic slip of 0° sample and 90° sample after hot compression with different deformations
![]()
图 7 不同变形量下高温压缩后0°试样和90°试样的小角度晶界分布
Figure 7. Low angle grain boundary distribution of 0° sample and 90° sample after hot compression with different deformations
-
[1] WU G H ,WANG C L ,SUN M ,et al. Recent developments and applications on high-performance cast magnesium rare-earth alloys[J]. Journal of Magnesium and Alloys,2021,9（1）：1-20. [2] 王硕,许道奎,王东亮,等. 超轻镁锂合金强化方法的研究现状[J]. 机械工程材料,2023,47（5）：94-101. WANG S ,XU D K ,WANG D L ,et al. Research progress on strengthening methods of ultra-lightweight Mg-Li alloy[J]. Materials for Mechanical Engineering,2023,47（5）：94-101.
[3] 刘华燊,孙有平,何江美,等. 轧制方式与速度对ZK60镁合金热轧板显微组织和力学性能的影响[J]. 机械工程材料,2023,47（12）：19-25. [4] ZHANG J H ,LIU S J ,WU R Z ,et al. Recent developments in high-strength Mg-RE-based alloys：Focusing on Mg-Gd and Mg-Y systems[J]. Journal of Magnesium and Alloys,2018,6（3）：277-291. [5] 李博超,范玲玲,崔壮,等. 异构镁制备及强韧化机理的研究现状[J]. 中国有色金属学报,2024,34（7）：2147-2172. [6] 陈佳俊,唐昌平,谢红梅,等. 双峰分布晶粒在铜、铝、镁合金中的研究进展[J]. 材料热处理学报,2022,43（3）：1-10. [7] ZHA M ,ZHANG H M ,YU Z Y ,et al. Bimodal microstructure-A feasible strategy for high-strength and ductile metallic materials[J]. Journal of Materials Science and Technology,2018,34（2）：257-264. [8] TANG C P ,LIU W H ,CHEN Y Q ,et al. Hot deformation behavior of a differential pressure casting Mg-8Gd-4Y-Nd-Zr alloy[J]. Journal of Materials Engineering and Performance,2017,26（1）：383-391. [9] FIGUEIREDO R B ,LANGDON T G. Principles of grain refinement in magnesium alloys processed by equal-channel angular pressing[J]. Journal of Materials Science,2009,44（17）：4758-4762. [10] FIGUEIREDO R B ,LANGDON T G. Grain refinement and mechanical behavior of a magnesium alloy processed by ECAP[J]. Journal of Materials Science,2010,45（17）：4827-4836. [11] TANG C P ,CUI L ,JIANG H C ,et al. The role of initial grain size on bimodal-grained microstructure and mechanical properties of an extruded Mg-Gd-Y-Nd-Zr alloy[J]. Journal of Materials Research and Technology,2023,23：4663-4677. [12] AL-SAMMAN T ,GOTTSTEIN G. Dynamic recrystallization during high temperature deformation of magnesium[J]. Materials Science and Engineering：A,2008,490（1/2）：411-420. [13] RONG W ,ZHANG Y ,WU Y J ,et al. The role of bimodal-grained structure in strengthening tensile strength and decreasing yield asymmetry of Mg-Gd-Zn-Zr alloys[J]. Materials Science and Engineering：A,2019,740：262-273. [14] LI B ,TENG B G ,WANG E D. Effects of accumulative rolling reduction on the microstructure characteristic and mechanical properties of Mg-Gd-Y-Zn-Zr sheets processed by hot rolling[J]. Materials Science and Engineering：A,2019,765：138317. [15] RAMEZANI S M ,ZAREI-HANZAKI A ,ABEDI H R ,et al. Achievement of fine-grained bimodal microstructures and superior mechanical properties in a multi-axially forged GWZ magnesium alloy containing LPSO structures[J]. Journal of Alloys and Compounds,2019,793：134-145. [16] CHUN Y B ,BATTAINI M ,DAVIES C H J ,et al. Distribution characteristics of in-grain misorientation axes in cold-rolled commercially pure titanium and their correlation with active slip modes[J]. Metallurgical and Materials Transactions A,2010,41（13）：3473-3487. [17] 郑子樵. 材料科学基础[M]. 2版. 长沙：中南大学出版社,2013. ZHENG Z Q. Fundamentals of materials science[M]. 2nd ed. Changsha：Central South University Press,2013.
[18] WANG B S ,XIN R L ,HUANG G J ,et al. Effect of crystal orientation on the mechanical properties and strain hardening behavior of magnesium alloy AZ31 during uniaxial compression[J]. Materials Science and Engineering：A,2012,534：588-593. [19] LIU X ,QIAN Y ,FAN Q B ,et al. Plastic deformation mode and α/β slip transfer of Ti-5Al-2.5Cr-0.5Fe-4.5Mo-1Sn-2Zr-3Zn titanium alloy at room temperature[J]. Journal of Alloys and Compounds,2020,826：154209. [20] GENÉE J ,SIGNOR L ,VILLECHAISE P. Slip transfer across grain/twin boundaries in polycrystalline Ni-based superalloys[J]. Materials Science and Engineering：A,2017,701：24-33. [21] LUSTER J ,MORRIS M A. Compatibility of deformation in two-phase Ti-Al alloys：Dependence on microstructure and orientation relationships[J]. Metallurgical and Materials Transactions A,1995,26（7）：1745-1756. [22] 梁瑞洋,杨平,毛卫民. 冷轧压下率及初始高斯晶粒取向度对超薄取向硅钢织构演变与磁性能的影响[J]. 材料工程,2017,45（6）：87-96. LIANG R Y ,YANG P ,MAO W M. Effects of cold rolling reduction and initial goss grains orientation on texture evolution and magnetic performance of ultra-thin grain-oriented silicon steel[J]. Journal of Materials Engineering,2017,45（6）：87-96.
[23] 董勇,刘吉兆. 初始取向对大应变轧制AZ31镁合金板材显微组织和力学性能的影响[J]. 中国有色金属学报,2014,24（7）：1700-1706. DONG Y ,LIU J Z. Effects of initial orientation on microstructure and mechanical properties of AZ31 magnesium alloy sheets fabricated by large strain rolling[J]. The Chinese Journal of Nonferrous Metals,2014,24（7）：1700-1706.
[24] 贾志伟,李莉,柳金龙,等. 初始组织和磁性能对激光刻痕处理取向硅钢铁损降幅的影响[J]. 上海金属,2022,44（1）：16-21. JIA Z W ,LI L ,LIU J L ,et al. Effect of initial microstructure and magnetic properties on iron loss reduction of oriented silicon steel after laser scribing[J]. Shanghai Metals,2022,44（1）：16-21.
下载:
计量
- 文章访问数: 7
- HTML全文浏览量: 6
- PDF下载量: 9
