ECAP处理后ZK40的组织及超塑性

研究了镁合金ZK40经等通道挤压1道次和4道次后的超塑性和微观组织.在523 K进行的拉伸实验表明，随着挤压道次的增加，ZK40的延伸率也得到了提高.实验通过对ZK40作不同条件下的拉伸测试，得到了超塑性表现最好的温度和应变速率.经4道次等通道挤压后的ZK40在523K的温度和1×10^-4/s的应变速率下其断裂延伸率达到了660%.微观组织的分析表明，ZK40在等通道处理过程中，晶粒随着挤压道次的增加不断细化，而且晶粒的等轴性和均匀性得到显著改善.     

大晶粒NiAl超塑性变形及其机理的研究

为解决本质脆性NiAl金属间化合物超塑性加工问题,研究了在高温条件下大晶粒度等原子比NiAl的超塑性变形行为及其机理.结果表明在1 000和1 100℃下,应变速率为1.67×10-4s-1～1.67×10-2s-1,该材料表现出超塑性行为.拉伸延伸率普遍超过200%,应变速率敏感性指数大于0.30.对拉伸试样的金相及TEM分析表明,在高温变形过程中,位错的运动包括滑移和攀移两种方式,超塑性是由动态回复及再结晶过程来实现的.     

AZ31镁合金轧制弱基面织构板材热变形行为研究

本文采用AZ31镁合金轧制弱织构板材进行热拉伸行为研究。使用Gleeble-3500型热模拟试验机,在变形温度为300℃～420℃、应变速率为0.001 s^-1～1.0 s^-1的条件下,进行高温拉伸试验,研究了变形参数对真实应力-应变曲线和样品微观组织的影响。同时,利用Arrhenius本构模型建立了本构方程,并依据试验结果绘制了热加工图。结果表明：合金的峰值应力和对应应变值随着温度的升高和应变速率的降低而不断减小。随着温度的升高,动态再结晶晶粒的体积分数明显减小,合金平均晶粒尺寸变大。当应变速率为0.1 s^-1,同时在低温(300℃, 340℃)时,合金发生完全动态再结晶,晶粒细小且分布均匀。另外,镁合金轧制弱织构板材的激活能Q为170.98 kJ/mol,且最佳热变形区域为变形温度300℃～350℃及应变速率0.01 s^-1～0.1 s^-1。     

Ti-6Al-4V合金超塑性变形行为的人工神经网络预测

为了研究钛合金的超塑性变形行为,对Ti-6Al-4V双相钛合金进行了超塑性变形试验.构建了以超塑性变形温度、应变速率、晶粒尺寸为输入变量且以峰值应力和稳态应力为输出变量的三层BP人工神经网络模型,预测了该合金在不同超塑性变形条件下的流变应力值,并对该模型的隐含层数、神经元个数、输入输出数据、算法函数进行了合理优化.结果...     

多道次搅拌摩擦加工制备的5083铝合金细晶材料超塑性研究

通过多道次搅拌摩擦加工5083铝合金材料,细化材料晶粒,使用倒置金相显微镜分析其晶体结构、微观形貌,然后对试样进行高温拉伸实验,通过分析其材料的延伸率、应力和应变的情况,研究试样材料的超塑性性能。研究表明:经过多道次搅拌摩擦加工后,材料晶粒细化均匀;通过高温拉伸试验,其延伸率是未进行加工的2.6倍。多道次搅拌摩擦加工成本较低,具备加工大面积铝合金材料的能力,这种加工方式在铝合金晶粒细化的加工中有着广阔的应用前景。     

快凝PM Al—Li合金高应变速率超塑性变形机制

对PM－Al-Li合金在高应变速率超塑性变形行为进行了研究,对其变形机制进行了讨论,研究表明,PM－Li合金在超塑变形过程中晶粒会发生形变诱发动态长大,其长大速率主要受应变速率所控制;在变形过程中,随着就变速率的增加,晶界滑动的协调机制由晶内位错滑移协调逐步向晶粒变形协调转变;PM－Al-Li合金在570℃以上变形时,绝热加热现象的发生会导致液相的产生,并且液相的体积分数随应速率的增加而增大,合金的延伸率随着液相体积分数的增加而急剧下降。     

热处理对一种两相钛合金超塑性及组织的影响

对经不同制度处理的一种富β的α+β型钛合金(SPZ)的超塑性性能及组织进行了研究.结果表明,700℃/1 h AC处理后,合金具有良好的室高温性能;应变速率高达1.11×10-3/s时,合金在740℃~800℃温度范围内显示出超塑性,超塑拉伸延伸率均超过1600%;760℃,合金拉伸延伸率可高达2149%.扫描电镜(SEM)观察发现,SPZ合金的变形行为具有明显细晶超塑性的特点.应变速率为2.22×10-3/s时,740℃、780℃变形后晶粒尺寸分别为1.51mm3、.21 mm.超塑变形后合金的晶粒尺寸比变形前的有所增大;超塑性温度越高,晶粒长大程度越高.     

不同初始组织材料超塑性m值模型与验证

为确定超塑性机理和本构方程,需要计算m值.采用铸造、轧制和退火方法获得细晶AA7075铝合金板材,采用高温拉伸机和图像分析仪研究了合金m值的变化,针对等轴晶粒和带状晶粒的材料超塑性变形,建立了m值与应变关系模型.模型证明等轴晶粒组织恒速度超塑性变形m值随应变增加而减小和带状晶粒组织超塑性变形m值随应变增加而增大.理论预测得到等轴细晶AA7075铝合金和AA7475+0.7Zr铝合金和带状晶粒的Mg-8.5%Li合金和包含小角度晶界的AA7475铝合金超塑性实验结果的支持.模型预测与实验结果吻合,内在组织变化是m值变化的根本原因.     

ZK60镁合金高应变速率锻造成形

采用Gleeble-1500对ZK60合金进行锻造模拟,分析了合金高应变速率可锻性;并采用空气锤对合金成功地进行高应变速率多向锻造,研究了其组织演变和力学性能。结果表明:高应变速率(≥10 s-1)锻造成形时,孪生和动态再结晶对变形储能的消耗以及变形温升对散热造成的塑性下降的弥补,可防止合金在高应变速率锻造时产生裂纹。此外,由于再结晶同时在晶界和孪晶上产生,获得了比低应变速率锻造成形更为均匀的再结晶组织,因此高应变速率锻造成形是一种高效可行的镁合金塑性加工工艺。经高应变速率多向锻造成形后,可形成壳状粗晶和核状细晶构成的双峰晶粒组织,应变∑Δε=2.64时,粗晶和细晶组织的平均晶粒尺寸分别为10μm和1μm。由于双峰晶粒组织的形成,合金表现出良好的综合力学性能,抗拉强度和延伸率分别达到330.2 MPa、24.8%,表明高应变速率多向锻造成形是制备高性能镁合金的有效途径。     

LF6防锈铝合金的超塑性实验研究

采用形变热处理工艺，使工业用ＬＦ６合金板材得到细小、等轴的晶粒组织。在５０５℃以初始应变速率ε＝１．６７×１０－４ｓ－１拉伸，得到最高延伸率４６５．５％，流动应力２．４９ＭＰａ．研究结果表明：拉伸过程中晶粒长大是由变形和热作用共同引起的。     

Property and microstructure analysis of ZK60 alloy superplastic sheet

It was investigated that the superplastic mechanical properties of fine-grained ZK60 magnesium alloy sheets at the temperature range of 200-420 ℃ and strain rate range of 5.56 × 10-4 -5.56 ×10-2 s-1 by tensile tests.And the microstructure evolution during the superplastic deformation of ZK60 magnesium alloy was examined by metallurgical microscope and transmission electronic microscope (TEM).The results showed that fine-grained ZK60 magnesium alloy starts to exhibit superplasticity from 250 ℃ and the maximum elongation is about 1106% at 400 ℃ and 5.56 × 10-4 s-1.The strain rate sensitivity is significantly enhanced with the increase of temperature and with the decrease of strain rate.The predominate superplastic mechanism of ZK60 magnesium alloy is grain boundary slide (GBS) at the temperature range of 300-400 ℃.The grains of ZK60 alloy remain equaxial after superplastic deformation,and dynamic continuous recrystallization (DCRX) is an important softening mechanism and grain stability mechanism during the superplastic deformation of the alloy.The curved grain boundaries and crumpled bands at grain boundaries after deformation prove GBS generates during superplastic deformation of ZK60 magnesium alloy.     

Superplastic deformation behavior and mechanism of 1420 Al-Li alloy sheets with elongated grains

True stress-true strain curve, microstructure and texture information were obtained to investigate the superplastic deformation behavior of 1420 Al-Li alloy sheets with initial elongated grains. From the true stress-true curve, the stress increases with the increase of strain to 0.15, then dramatically decreases with the increase of strain to 0.80, and finally keeps almost a horizontal line. Meanwhile, initial elongated grains are gradually changed into equiaxed grains and the initial strong Brass {0 1 1} 〈2 1 1〉 and S {1 2 3} 〈6 3 4〉 orientations are turned into nearly random orientation with increasing strain. All these results suggest that dislocation activity is the dominant mechanism during the first stage, then dynamic recrystallization occurs, and grain rotation is expected as an accommodation for grain boundary sliding (GBS). At larger strains, grain boundary migration (GBM) becomes necessary to accommodate GBS.     

Microstructure and flow stress of Mg-12Gd-3Y-0.5Zr magnesium alloy

The microstructure and flow stress of the Mg-12Gd-3Y-0.5Zr magnesium alloy was investigated by compression test at temperatures ranging from 350 to 500 ℃ and the strain rates ranging from 0.01 to 20 s-1. The flow stress of the magnesium alloy increased with strain rate and decreased with deformation temperature. Flow stress can be expressed in terms of the Zener-Hollomon parameter Z, which describes the combined influence of the strain rate and temperature using an Arrhenius function.The values of the deformation activation energy were estimated to be 245.9 and 171.5 kJ/mol at deformation temperatures below 400 ℃ and above 400 ℃, respectively. Two constitutive equations were developed to quantify the effect of the deformation conditions on the flow stress of the magnesium alloy. The effects of deformation temperature and strain rate on the microstructure of the magnesium alloy were also examined and quantified by measuring the volume fraction of dynamically recrystallized grain Xd. Xd increased with increasing of deformation temperature. When the deformation temperature was below 475 ℃, Xd decreased with strain rate until it reached 0.15 s-1, then it increased again. When the deformation temperature was above 475 ℃, Xd increased with strain rate.     

Ti-15-3合金高温变形的微观组织

Ti-15-3合金的组织和性能对工艺参数十分敏感，生产中不易获得组织和性能稳定一致的产品，通过在Gleeble-1500型热加工模拟试验机上进行的等温恒应变速率压缩试验和金相及透射分析，研究了变形温度、变形程度和变形速率对Ti-15-3合金热变形的显微组织的影响，分析表明，Ti-15-3合金高温变形时容易发生动态回复，高温大变形下低速变形时有发生少量的再结晶，这些研究对于制定该合金合理的热变形工艺，保证产品的质量和提高使用性能具有重要的理论价值和实际意义。     

Deformation behavior of Cu-12wt%Al alloy wires with continuous columnar crystals in dieless drawing process

The microstructure and mechanical properties of Cu-12wt%Al alloy wires which are composed of continuous columnar crystals after dieless drawing forming at drawing speed of 1.0―1.4 mm/s and deformation temperature of 600―900℃ were analyzed, and deformation behavior of the alloy during dieless drawing forming was experimentally investigated. The results showed that in the abovemen-tioned conditions, recrystallization phenomenon was not found during dieless drawing forming. When a drawing speed of 1.0 mm/s was...     

Superplasticity of Mg-5.8Zn-1Y-Zr alloy sheet fabricated by combination of extrusion and hot-rolling processes

Superplastic behaviors of quasicrystal phase containing Mg-5.8Zn-1Y-0.48Zr alloy sheets fabricated by combination of extrusion and hot-rolling processes have been investigated at temperature ranging from 623 to 753 K and at the strain rates ranging from 10-4 to 10-2 s-1 by uniaxial tensile tests. An excellent superplasticity with the maximum elongation to failure of 1020% was obtained at 753 K and the strain rate of 1.04×10-3 s-1 and its strain rate sensitivity, m, is as high as up to 0.75. The microstructure was stable during superplastic deformation due to the uniformly distributed fine quasicrystal particles. In addition, micro-cavities and their coalescences were observed in the superplastic deformation of the ZW61 magnesium alloy. Grain boundary sliding (GBS) was considered to be the main deformation mechanism during the superplastic deformation. Dislocation creep controlled by atom diffusion through grain boundaries or interior grains is suggested mainly to accommodate the GBS in super-plastic deformation.     

热循环峰值温度对2091Al－Li合金焊接HAZ显微组织和拉伸性能的影响

研究了焊接热循环峰值温度对２０９ｌＡｌ－Ｌｉ合金焊接ＨＡＺ显微组织和拉伸性能的影响。采用热模拟机模拟ＨＡＺ焊接热循环，对模拟试件进行拉伸试验、显微组织观察及断口分析。结果表明：随着峰值温度上升，焊接ＨＡＺ强度下降，而延伸率增高。     

动态时效对Al-Cu-Mg-Ag合金组织与力学性能的影响

对Al-Cu-Mg-Ag新型耐热铝合金进行预时效+中温轧制变形+终时效的动态时效工艺处理,采用硬度测试、拉伸性能测试,结合金相显微组织分析和透射电子显微分析,探究动态时效对其力学性能与微观组织的影响。结果表明：动态时效能够提高合金的时效硬化速率,随着变形量的增大,合金的峰时效时间逐渐减小,峰值硬度逐渐增大。动态时效能够改变晶粒形貌,随着变形量的增大,晶粒的纵横比增大,位错数量增多,强化相数量增多尺寸减小,使得合金强度随着变形量的增大而逐渐增大,但伸长率逐渐减小。变形量为50%合金的强度最高,抗拉强度和屈服强度最大,分别为527.4 MPa和467.0 MPa,伸长率保持在较高值9.1%。     

Al-5Fe-1.2Si-1Mg-0.6Cu-0.5Mn合金轧制变形行为及组织性能

为了细化Al-5%Fe基合金中粗大的脆性针状或针片状富铁相,采用电磁搅拌及固态挤压技术制备Al-5%Fe-1.2%Si-1%Mg-0.6%Cu-0.5%Mn合金轧制坯锭,研究Al-5%Fe基合金的轧制变形能力及合金的组织性能,并用热压缩实验模拟了铝铁合金在783~693K、变形速率为0.01~10s^-1条件下的热变形行为.结果表明：该合金高温变形时存在明显的稳态流变特征,流动应力对应变速率和温度敏感.板材力学性能较挤压态有大幅度提升,其室温下的抗拉强度和伸长率最高达到354.5MPa和7.6%,比挤压态分别提高了105.6%和184.6%.轧制对铝铁合金中富铁相的破碎作用十分明显.     

Plastic deformation behavior of ZK60 magnesium alloy with addition of neodymium

The hot deformation simulation of a ZK60 magnesiuln alloy at different temperatures from 373 to 673 K and different strain rates of 0.1, 0.01 and 0.002 s^-1 was studied by using the Gleebe-1500 simulator. The plastic deformation behavior was measured and the deformation activation energy was calculated. The microstructures of ZK60 magnesium alloy with an addition of neodymium during the deformation process were observed by using Polyvar-MET optical microscope and Tecnai G^2 20 TEM. The results show that the working hardening, the dynamic recovery and the dynamic recrystallization occur during the plastic deformation process at different temperatures and strain rates. The dynamic recrystallization starts when the temperature is over 473 K and the DRX grain size after hot deformation is only 5-10 μm. So the refined grains improve both the tensile strength and the elongation of alloys at room temperature. Neodymium is added into the alloy and a precipitate phase Mg12Nd that impedes the movement of dislocations is formed, which benefits to increasing mechanical properties of ZK60 magnesium alloy.