Effect of rolling and heat treatment on tensile behaviour of wrought Al-SiCp composites prepared by stir-casting

Al 6061- and Al 7108-SiCp composites (Al-PMMC) were prepared by stir-casting with SiCp size of 8 and 15 μm and volume fraction (Vf) of 0–20%. These composites were then subjected to successive hot rolling at 450 °C using a strain rate of 1 s⁻¹ while the intermediate period of heating between each two successive rolling steps was 1 min to 1 h. Tensile test was conducted on the as-rolled composite strips with 3.0, 1.1 and 0.4 mm thicknesses using 81, 94 and 98% reductions, subsequently, with a tensile rate of 10 MPa s⁻¹. Different tensile properties including ultimate tensile strength UTS, Young's modulus and elongation, were determined. The tensile behaviour was analysed in view of matrix alloy type and SiCp size and Vf. The effect of T6 treatment on the microstructure and tensile properties was also presented. Generally, successive hot rolling resulted in decreasing casting defects such as void and SiCp agglomeration present in the as-cast composites and hence enhanced mechanical properties were achieved. Almost 240 and 390% improvement in ultimate tensile strength (UTS) for 6061 and 7108 composite was obtained, respectively. The improvement in strength was remarkable for composites rolled to 0.4 mm. Annealing improved the elongation% at break of the 10–15% Vf composite more than 3 times. UTS of rolled composite was enhanced by T6 treatment at 176 °C and 120 °C for 6061 and 7108 composites. The effect of T6 treatment on the composite tensile behaviour was discussed.     

Microdistortion behavior of Al alloy reinforced by SiCp

Al alloy reinforced with SiCp was fabricated by the method of pressureless infiltration.The effects of factors such as SiCp size,volume fraction,matrix material and heat treatment process on microdistortion behavior of Al alloy were investigated.The results show that microdistortion decreases along with lessening of SiCp size and increasing of SiCp volume fraction.Matrix material has influence on the microdistortion behavior,and solution-aging can improve the microdistortion behavior.Stress and residual strain related to microdistortion behavior were simulated by FEM.It is found that the distribution of strain and stress is not symmetrical; residual strain and stress at interface are higher than those at the other places;at the sharp-angled area of a particle,matrix has the highest strain and stress where plastic distortion is caused at first;the microdistortion and stress far from the interface are smaller.     

高强合金钢50SiMnVB动态再结晶模型研究

通过热模拟压缩试验研究了50SiMnVB合金钢在应变速率为0.01-10s-1、温度为800-1000 ℃条件下的高温热变形行为.利用金相显微镜观察了合金压缩变形后的显微组织,结果表明:50SiMnVB合金钢在高温热变形过程中发生了典型的动态回复和动态再结晶行为,其中,动态再结晶以连续再结晶的形式进行,且应变速率越小、...     

6061铝合金低温快速流变行为的研究

采用圆柱体试样，在Gleeble-1500型动态热模拟试验机上进行低温快速压缩试验，研究了6061铝合金低温下快速变形的流变行为，并分析了其变形组织。结果表明，6061铝合金的流变应力随变形温度升高而降低，随应变速率提高而增大；在高应变速率下，发生了不连续动态再结晶；温升强烈地受变形程度的影响；低温快速变形可获得晶粒细小的组织。     

Kinetics and critical conditions for initiation of dynamic recrystallization during hot compression deformation of AISI 321 austenitic stainless steel

Dynamic recrystallization behavior of AISI 321 austenitic stainless steel were studied using hot compression tests over the range of temperatures from 900 °C to 1200 °C and strain rates from 0.001 s^-1 to 1 s^-1. The critical strain and stress for initiation of dynamic recrystallization were determined by plotting strain hardening rate vs. stress curves and a constitutive equation describing the flow stress at strains lower than peak strain. Also, the strain at maximum flow softening was obtained and the effect of deformation conditions (Z parameter) on the critical strain and stress were analyzed. Finally, the volume fraction of dynamic recrystallization was calculated at different deformation conditions using these critical values. Results showed that the model used for predicting the kinetics of dynamic recrystallization has a great consistency with the data, in the form of θ-ε curves, directly acquired from experimental flow curves.     

铸态ER8车轮钢的热变形行为及本构模型研究

采用Gleeble-1500D热模拟试验机,在变形温度为900～1250℃、应变速率为0.001～1 s-1的条件下对铸态ER8车轮钢进行热压缩试验,得到真应力-真应变曲线.结果发现:其真应力-真应变曲线符合动态再结晶型软化机制,变形初始阶段,材料发生硬化,真应力快速增加,随着变形的继续,材料发生动态回复,加工硬化速率...     

低温处理对SiCp／6061Al复合材料残余应力的影响

对时效状态及－６０℃和－１９６℃低温处理状态的Ｓｉｃ_ｐ／６０６１Ａｌ（ＳｉＣ体积分数为２０％）复合材料中的热残余应力进行了Ｘ射线应力测定及有限元分析．实验与计算结果均表明，随着低温处理温度的下降，复合材料基体相中的平均残余应力由拉应力逐渐变成了压应力，增强相中的平均残余应力由压应力逐渐变成了拉应力．但是，低温处理后材料内部仍然存在着应力梯度和应力集中，基体相中仍然存在着拉应力区．     

Hot deformation behavior and microstructure evolution of a Mg–Gd–Nd–Y–Zn alloy

The hot deformation behavior of homogenized Mg–6.5Gd–1.3Nd–0.7Y–0.3Zn alloy was investigated during compression at temperatures of 250–400 ℃ and at strain rates ranging from 0.001 to 0.100 s~(-1). Microstructure analyses show that the flow behaviors are associated with the deformation mechanisms. At the lower temperatures(250–300 ℃), deformation twinning is triggered due to the difficult activation of dislocation cross-slip. Dynamic recrystallization(DRX) accompanied by dynamic precipitation occurs at the temperature of 350 ℃ and influences the softening behavior of the flow.DRX that develops extensively at original grain boundaries is the main softening mechanism at the high temperature of 400 ℃ and eventually brings a more homogeneous microstructure than that in other deformation conditions. The volume fraction of the DRXed grains increases with temperature increasing and decreases with strain rate increasing.     

AZ31镁合金铸轧和常规轧制板的变形组织及形变特征

在变形温度为150～400 ℃、应变速率为0.3～0.000 3 s~(-1)条件下,在Gleeble1500热模拟机上采用等温拉伸试验对AZ31镁合金铸轧和常规轧制板的高温塑性及组织演变进行研究.结果表明:两种AZ31镁合金板的峰值应力和峰值应变均随着变形温度的降低和应变速率的增加而逐渐增大.铸轧板的应变硬化指数和应变速率敏感系数均大于常规轧制板的.在高温低应变速率变形条件下,铸轧板的晶界滑移引起的空洞尺寸、体积分数和密度均大于常规轧制板的.低应变速率下拉伸变形后的动态再结晶晶粒尺寸随温度的升高逐渐增加;不同变形条件下铸轧板的晶粒尺寸均小于常规轧制板的;再结晶晶粒尺寸和Z参数呈幂律关系.     

BT25钛合金β相区动态再结晶行为及数值模拟

利用Gleeble-3500 型热模拟试验机对BT25 钛合金进行单道次等温压缩实验,分别采用Najafizadeh-Jonas 加工硬化率模型和Cingara-McQueen 流变应力模型研究了合金在变形温度1040～1100℃,应变速率0.001～1 s-1 和最大压下率为60％的条件下动态再结晶的临界条件,分析真...     

电子封装用SiC_p/铝基复合材料的触变性能

采用Gleeble-1500热模拟机,研究了半固态SiCp/铝基复合材料在不同触变温度和变形速率下的触变性能和组织特征。结果表明,随着应变的增加,复合材料应力首先快速增加,然后快速减小,最后又有缓慢增加的趋势。此外,随着变形温度降低或变形速率升高,复合材料的半固态压缩变形应力均增加。经过压缩变形后,自由变形区比大变形区分布有更多的SiCp,含量达到55%(体积分数)左右,且平均尺寸小于20μm。细SiCp在压缩变形后主要集中于自由变形区,这表明通过半固态触变成形产生的液固相分离可产生高SiCp区域,从而符合电子封装材料的要求。     

Effect of Hot Deformation on Texture and Microstructure in Fe-Mn Austenitic Steel During Compression Loading

Hot compression tests of a new high-Mn austenitic steel were carried out at deformation temperatures of 700, 800, 900, and 1000 °C under strain rate of 0.01 s^?1. The hot deformation behavior was investigated by the analyses of flow curves, texture, and deformed microstructures. Microstructures of the deformed specimens and macrotexture were examined using electron backscatter diffraction and x-ray diffraction methods, respectively. The results showed that the flow stress depended strongly on the deformation temperature and decreased by increasing deformation temperature. The microstructural evidence indicated that the dynamic recrystallization (DRX) process of experimental steel was initiated at 800 °C with necklace structure. The volume fraction of DRX grains was considerably increased by increasing deformation temperature to 1000 °C. Texture of the DRX grains tended to become a weak texture and was associated with the formation of Goss and R-Cube components. Meanwhile, martensitic transformation was detected in the hot-deformed austenite. The martensitic transformation was the most difficult in the DRX grains because of the effect of small grain size. The tendency of transformation was decreased after compression at 1000 °C.     

The Precipitation Behavior and Hot Deformation Characteristics of Electron Beam Smelted Inconel 740 Superalloy

The Inconel 740 superalloy was prepared by the electron beam smelting (EBS) technology, the precipitation behavior and strengthening mechanism were studied, and the hot deformation characteristics of EBS 740 superalloy were investigated. The results indicate that the EBS 740 superalloy is mainly strengthened by the mechanism of weakly coupled dislocation shearing, and the resulting critical shear stress is calculated to be 234.6 MPa. The deformation parameters show a great influence on the flow behavior of EBS 740 superalloy. The strain rate sensitivity exponent increases with the increasing of deformation temperature, and the strain hardening exponent shows a decreasing trend with the increasing of strain. The activation energy of EBS 740 above 800 °C is measured to be 408.43 kJ/mol, which is higher than the 740H superalloy. A hyperbolic-sine-type relationship can be observed between the peak stress and Zener–Hollomon parameter. Nevertheless, the influence of deformation parameters is found to be considerably different at temperatures below and above 800 °C. The size of dynamic recrystallization (DRX) grains decreases with the increasing of strain rate when the strain rate is lower than 1/s, and reverse law can be found at higher strain rate. As a result, a piecewise function is established between the DRX grain size and hot working parameters.     

变形条件对SiCp/2014Al复合材料力学行为和晶粒度的影响

研究了变形温度,应变速率和变形程度等热加工参数对ＳｉＣｐ／２０１４Ａｌ复合材料力学行为和晶粒度的影响。结果表明,该材料的流动应力对变形温度和应变速率比较敏感。变形每升高４０℃,流动应力降低５￣１０ＭＰａ,应变速率每提高一个数量级,流动应力增加１．３￣１．８们。提高应变整编有利于获得细晶组织。以足够的变形程度锻造以及适当提高锻后冷却速度均有利于获得细晶组织。根据实验结果确定了该材料的流动应力与热加工     

Constitutive Equation and Processing Map for Hot Deformation of SiC Particles Reinforced Metal Matrix Composites

Flow behavior and microstructures of Al/15% SiCp were investigated by hot compression tests using Gleeble-1500 thermomechanical simulator at temperatures ranging from 440 to 500 °C with strain rates of 0.001-1.0 s⁻¹. The high-temperature deformation behaviors of Al/15% SiCp were analyzed based on the true stress-true strain curves. The results show that the softening mechanism at low strain rate (0.001 s⁻¹) is dynamic recovery, and at high strain rates (0.01, 0.1, and 1 s⁻¹) is dynamic recrystallization (DRX). Based on these experimental data, a set of constitutive equations for Al/15% SiCp are described by the Zener-Hollomon parameter, and the coefficients of equations are found to be functions of strain. The constitutive equations reveal the dependence of flow stress on strains, strain rates, and temperatures. Furthermore, the mean error between the experimental and the calculated flow stress was computed. The result shows that the calculated results from constitutive equations are in good agreement with the experimental results. To demonstrate the potential workability of Al/15% SiCp, the processing map was established. The stable zones and the instability zones in processing map are identified and verified through micrographs. As a result, the optimum strain rates and temperatures for effective hot working of Al/15% SiCp were determined.     

SiCp/6061Al合金复合材料的单轴循环变形行为及其时间相关特性

对T6热处理后的6061Al合金与SiCp／6061Al合金复合材料（14％,21％SiCp）的室温单轴循环变形行为进行了实验研觅讨论了基体合金和其复合材料在不同加载条件下的循环软／硬化行为和棘轮变形特征．实验研究表明：复合材料在宏观层次上体现出与基体相类似的应变循环特性和棘轮变形规律,即复合材料在非对称应力循环下也将产生一定的棘轮变形,并随应力幅值和平均应力的增加而增加;颗粒的引入使复合材料抵抗棘轮变形的能力增强,棘轮变形随颗粒含量升高而下降;复合材料的棘轮行为具有明显的时间相关特性,棘轮应变值依赖于应力率和峰值保持时间．研究得到了一些有助于复合材料循环变形行为本构描述的结论．     

Microstructure characterization of Al-cladded Al–Zn–Mg–Cu sheet in different hot deformation conditions

Al-cladded Al–Zn–Mg–Cu sheets were compressed up to 70% reduction on a Gleeble–3500 thermo-mechanical simulator with temperatures ranging from 380 to 450 °C at strain rates between 0.1 and 30 s^?1. The microstructures of the Al cladding and the Al–Zn–Mg–Cu matrix were characterized by electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD). The microstructure is closely related to the level of recovery and recrystallization, which can be influenced by deformation temperature, deformation pass and deformation rate. The level of recovery and recrystallization are different in the Al cladding and the Al–Zn–Mg–Cu matrix. Higher deformation temperature results in higher degree of recrystallization and coarser grain size. Static recrystallization and recovery can happen during the interval of deformation passes. Higher strain rate leads to finer sub-grains at strain rate below 10 s^?1; however, dynamic recovery and recrystallization are limited at strain rate of 30 s^?1 due to shorter duration at elevated temperatures.     

Al-Mg-Si 合金的高温流变过程动态再结晶研究

采用热力模拟试验机对Al-0.83Mg-0.59Si铝合金进行热压缩实验,研究了变形温度300～500 ℃、变形速率0.001～10 s-1下材料的动态再结晶行为。实验得到Al 0.83Mg 0.59Si合金在300～500 ℃变形时,软化机制以动态再结晶为主;流变应力会随着变形温度的降低和变形速率的升高而升高,较低变形速率下,动态再结晶行为更充分,应力软化现象更明显。统计实验所得流变应力曲线数据,建立了热变形本构方程,确定了合金热变形激活能Q为480.243 kJ/mol 。基于加工硬化率曲线,建立了其动态再结晶临界应变模型。结果表明,Al-0.83Mg-0.59Si铝合金的流变应力随温度的升高和变形速率的降低而降低,动态再结晶是其主要的软化机制。临界应力与峰值应力存在线性关系：σc=0.85σp-5.061 58。引入Zener Hollomon参数来描述变形条件对临界条件的影响,得到临界应变与Z参数的关系为：εc=0.000 134Z0.051 64。     

ZL270LF铝合金的热变形行为与组织演变

通过热压缩实验研究了ZL270LF铝合金在变形量为70%,温度为300~550 ℃,应变速率为 0.01~10 s^-1范围的热变形行为,建立了流变应力本构方程模型,绘制出了二维热加工图,确定了最佳热加工区域,采用电子背散射衍射（EBSD）和透射电子显微镜（TEM）技术研究了该合金的组织演变规律。结果表明：ZL270LF铝合金的流变应力随变形温度的升高和应变速率的降低而降低,热变形激活能为309.05 kJ/mol,最优热加工区为温度470~530 ℃、应变速率为0.01~1 s^-1。该合金在热变形过程中存在3种不同的DRX机制,即连续动态再结晶（CDRX）、不连续动态再结晶（DDRX）和几何动态再结晶（GDRX）,其中CDRX是ZL270LF铝合金动态再结晶的主要机制。     

Dynamic Recrystallization during Hot Deformation of 304 Austenitic Stainless Steel

The kinetics of dynamic recrystallization (DRX) during hot compression of 304 austenitic stainless steel was studied over the temperature range of 900-1200 °C and strain rate range of 0.002-0.1 s^?1. The initiation and evolution of DRX were investigated using the process variables derived from flow curves. By the regression analysis for conventional hyperbolic sine equation, the activation energy for DRX was determined as Q = 475 kJ mol^?1. The temperature and strain rate domain where DRX occurred were identified from the strain rate sensitivity contour map. The critical stress (and strain) for the initiation of DRX was determined from the inflection point on the work hardening rate (θ = dσ/dε) versus flow stress (σ) curve. The saturation stress of the dynamic recovery (DRV) curve was calculated from the θ-σ plot at the same condition at which DRX occurred. Progress of fraction recrystallization was determined from the difference between the generated DRV curve and the experimental DRX curve. In addition, the microstructural evolution at different strain levels during DRX was characterized and compared with the calculated fraction recrystallization.