轧制工艺对Mg-10Gd-4.8Y-0.6Zr合金显微组织和力学性能的影响

Mg-10Gd-4.8Y-0.6Zr铸态合金经525℃、16 h均匀化退火后,在500℃轧制成总变形量为84%的板材,轧制后在200℃进行时效处理。观察合金的微观组织变化,并测试合金的力学性能。结果表明:轧制变形明显细化了晶粒尺寸,轧制后组织中存在方块相和长条状相;轧制初期组织中存在大量孪晶,孪晶能很好地协调塑性变形,并诱发了孪生动态再结晶;随着轧制变形量的增大,孪晶数量减少,再结晶方式以晶界弓出形核为主。轧制T5态合金具有优异的高温力学性能,200、250、300和350℃时抗拉强度分别为392、381、251和112 MPa,350℃拉伸时伸长率达到107.0%。     

挤压温度对Mg-1Gd合金织构演变的影响

采用电子背散射衍射(EBSD)分析方法观察了Mg-1wt%Gd合金在退火过程中的织构演变,研究了挤压温度和退火温度对微观组织及织构的影响。结果表明:在低温挤压下,剪切带形核是主要的再结晶机制,退火后形成了很强的2织构类型;而在高温挤压下,剪切带数量较少,退火后织构几乎没有发生变化。因此,剪切带上的形核及2晶粒的择优取向生长是Mg-1Gd合金中2织构形成的主要原因。     

Mg-4Zn-0.5Er-1Y镁合金板材的组织与力学性能

研究了Mg-4Zn-0.5Er-1Y变形合金轧制板材在经200～380℃,保温0.5～4h退火处理后,合金显微组织的演变及其力学性能的变化规律。结果表明,该合金退火后均出现明显的动态再结晶组织,且晶粒比较细小,基体中存在大量含有稀土元素的第二相,这些第二相在热轧状态下破碎成细小的颗粒,促进了动态再结晶晶粒的异质形核。合金退火处理后的强度较原轧制态降低,但塑性却得到明显的改善。最佳退火温度为350℃,保温0.5h后晶粒尺寸约为8μm,抗拉强度为276MPa,伸长率达到最大为22.5%。经过计算可知,该合金再结晶晶界迁移激活能为22.76kJ/mol,同时建立了该合金再结晶晶粒长大的动力学模型。     

孪晶类型对AZ31镁合金静态再结晶的影响

对轧制下压方向平行和垂直晶粒c轴的两类板材进行150℃轧制(5%下压量)后,利用背散射电子衍射分析(EBSD)研究了轧制试样中不同类型的孪晶组织对静态再结晶的晶粒形核、微观组织及织构的演变的影响。结果表明:含有大量{1011-}-{1012-}双孪晶的样品中,二次孪生有效促进再结晶形核,显著细化晶粒。再结晶晶粒取向规律性不强,有效削弱基面织构。而含有大量{1012-}拉伸孪晶的样品,拉伸孪晶不能有效促进再结晶形核。退火过程中基体不断长大,当再结晶驱动力足够大时,基体会吞并周围拉伸孪晶,同时诱发织构改变,基体取向的织构逐渐增强,拉伸孪晶取向的织构逐步减弱。     

汽车用Mg-6Zn-0.55Zr合金的轧制工艺研究

对挤压态Mg-6Zn-0.55Zr合金进行了轧制试验,并采用光学显微镜、万能试验机研究了轧制及轧制后退火对挤压态Mg-6Zn-0.55Zr合金显微组织与力学性能的影响。结果表明:挤压态合金经轧制温度320℃,道次压下率为60%、30%、10%的3道次轧制,板材边缘无裂纹产生,表面质量良好。轧制态合金的晶粒内有大量孪晶与位错,经240℃×1 h退火后,合金完全静态再结晶,等轴晶粒较为细小、均匀,合金的抗拉强度和伸长率分别达到316 MPa和29.6%,综合力学性能最佳。     

Mg-4.4Li-2.5Zn-0.46Al-0.74Y合金高温变形流动应力、组织演变与本构分析

采用多向锻造与轧制(MDFR)制备了 Mg-4.4Li-2.5Zn-0.46Al-0.74Y合金,利用拉伸机、OM和XRD等研究了热拉伸流动应力、组织演变、本构模型与变形机理.结果表明,合金多向锻造晶粒细化机理为机械式剪切破碎与动态再结晶细化.合金在523～573 K时,热变形组织主要发生动态回复与动态再结晶;≥573 K时,热变形组织主要发生晶粒长大;在623 K发生由晶粒长大引起的应变硬化.合金退火组织由α(Mg)、β(Li)、Al2Y、Al12Mg17、LiAl和Mg2Y相组成.本构分析表明,合金应力指数为4.4,变形激活能为120.40 kJ/mol;623 K、1.67×10-4s-1条件下,对应240％延伸率的位错密度和数量与原子扩散计算表明,合金在该条件下的变形机理为晶格扩散控制的位错蠕变.晶粒长大模型确定该条件下的晶粒长大指数q= 2,比例因子α'= 0.2.     

GH4169合金非均匀组织在加热过程中的演化机理

通过对第二相状态、晶界取向差及晶粒尺寸演化的分析,研究了GH4169合金不均匀组织在加热过程中的演化机理.结果表明,GH4169合金中d相的体积分数在低温下随温度的升高和时间的延长而增加;在高温时随温度的升高而降低,随时间的延长先增加后降低至恒定值.第二相的钉扎作用表现为:晶内析出的d相和g"相阻碍位错的运动,沿晶界析出的d相阻碍再结晶晶粒的形核和长大,碳化物阻碍晶粒长大.小角度晶界的体积分数随加热温度的升高和时间的延长而降低;高温下,退火孪晶的生长使得小角度晶界含量增加.GH4169合金的组织演化机理主要包括:亚晶长大、再结晶晶粒的长大和退火孪晶的长大.新的再结晶晶粒主要通过亚晶长大过程获得,亚晶长大过程主要通过小角度晶界的转动和位错的迁移完成.晶粒长大过程受到抑制时,合金通过退火孪晶的形核及长大耗散其吸收的热量.     

AZ31镁合金中拉伸孪晶静态再结晶的分析

基于前期工作对压缩孪晶静态再结晶的分析,主要利用XRD和EBSD技术进一步研究AZ31镁合金中拉伸孪晶静态再结晶过程中组织和织构的演变规律,以及再结晶初期新晶粒的取向特征,结果表明:拉伸孪晶不能有效地促进再结晶形核,其细化晶粒的效果不显著,其再结晶速率显著延迟于压缩孪晶;退火过程中并没有生成新的再结晶织构组分,表现为初始基面织构的减弱;新晶粒优先在拉伸孪晶的变体交叉处,或拉伸孪晶与压缩孪晶的交叉处形核,但其取向规律性不强,没有遵循初始拉伸或压缩孪晶内的取向规律,同时还对拉伸与压缩孪晶的再结晶行为进行了比较。     

静态退火对Mg-Gd-Y-Zr挤压合金的微结构与织构影响

本文研究了Mg-9Gd-4Y-0.6Zr挤压合金在静态退火过程中的微结构与织构的演变。采用金相显微术、扫描电子显微术、透射电子电子显微术、差热分析仪、XRD织构测试仪及EBSD分析技术表征了合金的晶粒长大、析出相沉淀及织构改变。结果表明,退火初期的晶粒尺寸下降是由再结晶引起的;晶间不均匀变形诱发了晶间的局部析出,继而抑制了再结晶过程。织构分析表明,热挤压产生了常见的基面纤维织构和不常见的柱面纤维织构,即c轴平行于挤压方向;在静态再结晶过程中,新晶粒形核会弱化柱面纤维,而晶粒长大过程会强化柱面纤维。晶界与亚晶界上的大量析出相抑制了织构改变。     

退火温度对铝钛强韧的CrCoNi中熵合金组织与性能的影响

通过电子背散射衍射(EBSD)和维氏硬度测试,研究不同退火温度下新型铝钛强韧的CrCoNi中熵合金组织演变规律和硬度变化。结果表明,退火温度较高(1100℃)时,合金的退火孪晶密度较高,且孪晶形貌更加平直规整;再结晶和晶粒长大和退火温度并非简单的线性关系,超过临界温度合金再结晶和晶粒长大过程明显加快,在1100℃下退火1 h可得到平均晶粒尺寸20.89μm的等轴晶组织,由于加工应力释放,合金硬度下降到302.9 HV0.2。     

Annealing behaviour of Mg-3Al-1Zn alloy sheet obtained by a combination of high-temperature rolling and subsequent warm rolling

The recrystallization and grain growth behaviour of Mg-3Al-1Zn alloy sheets with a deformation microstructure, obtained by a combination of high-temperature rolling and subsequent warm rolling, was investigated at different stages of annealing. The basal texture was significantly weakened as a result of the formation of new grains with a largely altered c-axis orientation relative to the initial basal orientation owing to discontinuous static recrystallization during primary recrystallization. The new grains nucleated mostly at the pre-existing grain boundaries rather than at the intersections of twins or within the twins. Subsequent grain growth led to further progression of the texture weakening accompanied by an enhancement in the basal pole inclination.     

Mg-7Gd-5Y-1Nd-xZn-0.5Zr(x=0,1,2)挤压态合金微观组织和力学性能

采用扫描电子显微镜、电子背散射衍射、透射电子显微镜、高角度环形暗场?扫描透射,分析了Mg-7Gd-5Y-1Nd-xZn-0.5Zr(x=0,1,2,质量分数,%)挤压态合金微观组织结构和力学性能,旨在探索Zn对于合金性能影响的微观机制。结果表明:在Mg-7Gd-5Y-1Nd-0.5Zr合金中添加Zn元素,不仅形成LPSO结构,也促进了Mg5(RE,Zn)颗粒的析出,并与Zr形成Zn-Zr相。LPSO结构不仅能阻碍晶粒长大,细化晶粒;也能够阻碍动态再结晶,从而形成动态再结晶晶粒和变形晶粒共存的双模结构,动态再结晶晶粒为á0001?//ED织构,变形晶粒为á1010?//ED织构。微米级大尺寸Mg5(RE,Zn)颗粒会导致应力集中,引起裂纹的萌生,降低合金的塑性;均匀分布的亚微米级Mg5(RE,Zn)颗粒起第二相强化作用,并能钉扎晶界,阻碍晶粒长大。对比3种挤压态合金,Mg-7Gd-5Y-1Nd-2Zn-0.5Zr合金获得了最优的力学性能,其抗拉强度、屈服强度和伸长率分别为365 MPa、276 MPa和17.5%。     

Relating Initial Texture to Deformation Behavior During Cold Rolling and Static Recrystallization Upon Subsequent Annealing of an Extruded WE43 Alloy

Deformation behaviors during cold rolling and static recrystallization behaviors upon subsequent annealing of an extruded WE43 alloys with different initial textures were investigated in this study. Three types of differently textured WE43 initial alloys were labeled as samples I, II and III. The results showed that multiple twinning modes and basal slip dominated the deformation of samples during cold rolling. Cold-rolled sample I activated the larger number of double twins with high strain energy, accompanied by the more uniform strain distribution, than cold-rolled samples II and III. During subsequent annealing, recrystallized grains preferentially occurred in double twins, twin-twin intersections and grain boundaries, thereby making cold-rolled sample I have the more rapid recrystallization rate. Similar recrystallization textures formed in three types of cold-rolled samples at the recrystallization nucleation stage, and they never largely changed with the annealing time due to the uniform grain growth induced by the solute drag and the precipitation pinning at grain boundaries. After full recrystallization, the grain growth was controlled by the solute drag, instead of precipitates which were re-dissolved into the matrix. Finally, the nucleation and growth kinetics of static recrystallization were calculated, and the effects of initial texture on activation energies of recrystallization nucleation and growth were discussed.     

MICROSTRUCTURES AND PROPERTIES OF RECIPROCATINGLY EXTRUDED Mg-6.4Zn-1.IY ALLOYS

An icosahedral Mg3 YZn6 quasicrystalline phase can be produced in Mg-Zn-Y system alloys when a proper amount of Zn and Y is contained, and it is feasible to prepare the quasicrystal phase-reinforced low-density magnesium alloy. In this article, phase constituents and the effect of reciprocating extrusion on microstructures and properties of the as-cast Mg-6.4Zn-1.1 Y alloy are analyzed. The microstructure of the as-cast Mg-6.4Zn-1.1 Y alloy consists of the a-Mg solid solution, icosahedral Mg3 YZn6 quasicrystal, and Mg3 Y2Zn3 and MgZn2 compounds. After the alloy was reciprocatingly extruded for four passes, grains were refined, Mg3 Y2 Zn3 and MgZn2 phases dissolved into the matrix, whereas, Mg3YZn6 precipitated and distributed uniformly. The alloy possesses the best performance at this state; the tensile strength, yield strength, and elongation are 323.4 MPa, 258.2 MPa, and 19.7%, respectively. In comparison with that of the as-cast alloy, the tensile strength, yield strength, and elongation of the reciprocatingly extruded alloy increase by 258.3%, 397.5%, and 18 times, respectively. It is concluded that reciprocating extrusion can substantially improve the properties of the as-cast Mg-6.4Zn-1.1 Y alloy, particularly for elongation. The high performance of the Mg-6.4Zn-1.1 Y alloy after reciprocating extrusion can be attributed to dispersion strengthening and grain-refined microstructures.     

Microstructure and Texture Evolution of Mg-14Gd-0.5Zr Alloy during Rolling and Annealing under Different Temperatures

Mg alloys containing high rare earth (RE) elements are hard to be rolled due to their low ductility and high strength at low temperatures. Therefore, rolling at high temperatures is necessary for these alloys. In this work, a Mg-14Gd-0.5Zr (wt%) alloy was rolled one pass with 40% reduction at high temperatures over 450 °C. The effects of rolling temperature on the microstructure and dynamic recrystallization behavior were analyzed in detail by the electron backscattered diffraction (EBSD) method. The results revealed that the alloy shows good rollability at high temperature due to the activity of non-basal dislocations and twins. However, dynamic recrystallization is difficult to take place because of the easy activation of multi-slip system and thus more accumulated strain energy. However, Gd segregation was observed at the grain boundary and it is inferred that the segregation can partially enhance the dynamic recrystallization ratio. Statically recrystallized grains with large size took place after short-term inter-pass annealing treatment ranging from 450 °C to 500 °C, and formed basal texture. The result suggests that the formation of basal texture during short-term annealing treatment was attributed to the growth of dynamic recrystallized grains caused by weakened Gd segregation.     

Nd对铸态及轧制态Mg-Zn-Y合金组织及性能的影响

在Mg-3.5Zn-0.6Y合金中添加不同含量(0、0.4%、0.8%、1.2%)的稀土元素Nd,研究其对Mg-3.5Zn-0.6Y合金铸态及轧制态显微组织与力学性能的影响。结果表明,添加0.4%、0.8%的Nd的合金晶粒较细小,呈等轴晶,并且含有Mg41Nd5和Mg24Y5相。镁合金在热轧时第二相被破碎,晶粒变得更加细小。铸态合金经400℃×12h扩散退火,轧制态合金经400℃×0.5h退火后抗拉强度及伸长率最大,分别为234MPa、14.6%和265MPa、11.7%。     

Microstructure and mechanical properties of extruded Mg-6.5Gd-1.3Nd-0.7Y-0.3Zn alloy

The Mg-6.5Gd-1.3Nd-0.7Y-0.3Zn alloy ingot and sheet were prepared by casting and hot extrusion techniques,and the microstructure,age hardening behavior and mechanical properties were investigated.The results show that the as-cast alloy mainly containsα-Mg solid solution and compounds of Mg5RE and Mg24RE5(RE=Gd,Y and Nd)phases.The grain size is refined after hot extrusion,and the Mg5RE and Mg24RE5 compounds are broken during the extrusion process.The extruded alloy exhibits remarkable age hardening response and excellent mechanical properties in the peak-aging state.The ultimate tensile strength,yield strength and elongation are 310 MPa,201 MPa and 5.8%at room temperature,and 173 MPa,133 MPa and 25.0%at 300℃,respectively.     

MICROSTRUCTURE OF Mg-6.4Zn-1.1Y ALLOY FABRICATED BY RAPID SOLIDIFICATION AND RECIPROCATING EXTRUSION

In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1 Y magnesium alloy with a thickness of 50-60 um were obtained by a melt spinning single-roller device, and the flakes were then processed into rods by reciprocating extrusion and direct extrusion. The microstructure of the alloy was analyzed by optical microscope and SEM, and the constituent phases were identified by XRD. Phase transformation and its onset temperature were determined by differential thermal analyzer (DTA). The analysis result shows that rapid solidification for Mg-6.4Zn-1.1Y alloy can inhibit the eutectic reactions, broaden the solid solubility of Zn in a-Mg solute solution, and impede the formation of Mg3 Y2 Zn3 and MgZn2 compounds, and thus help the icosahedral Mg3 YZn6 quasicrystal formed directly from the melt. The mierostrueture of the flakes consists of the a-Mg solid solution and icosahedral Mg3 YZn6 quasierystal. Dense rods can be made from the flakes by two-pass reciprocating extrusion and direct extrusion. The interfaces between flakes in the rods can be welded and jointed perfectly. During the reciprocating extrusion and direct extrusion process, more Mg3 YZn6 compounds are precipitated and distributed uniformly, whereas the rods possess fine microstructures inherited from rapidly solidified flakes. The rods contain only two phases: amagnesium solid solution as matrix and fine icosahedral Mg3 YZn6 quasicrystal which disperses uniformly in the matrix.     

Microstructure and mechanical properties of Mg-6Al magnesium alloy with yttrium and neodymium

The effects of rare earth (RE) elements Y and Nd on the microstructure and mechanical properties of Mg-6Al magnesium alloy were investigated. The results show that a proper level of RE elements can obviously refine the microstructure of Mg-6Al magnesium alloys, reduce the quantity of/β-Mg17Al12 phase and form Al2Y and AI2Nd phases. The combined addition of Y and Nd dramatically enhances the tensile strength of the alloys in the temperature range of 20-175℃. When the content of RE elements is up to 1.8%, the values of tensile strength at room temperature and at 150℃ simultaneously reach their maximum of 253 MPa and 196 MPa, respectively.The main mechanisms of enhancement in the mechanical properties of Mg-6Al alloy with Y and Nd are the grain refining strengthening and the dispersion strengthening.