等通道侧向挤压和板材挤压法制备细晶ZK60镁合金板材的热剪切变形本构分析（英文）

采用不同道次等通道侧向挤压(DECLE)和板材挤压成形发制备细晶ZK60合金板材。经过3和5道次DECLE和后续挤压后,退火样品中的粗大晶粒(68μm)分别变为6.0μm和5.2μm的细小晶粒。基于冲孔剪切实验(SPT)结果建立本构方程,研究合金的热剪切变形行为。SPT的温度范围为200～300℃,应变率范围为0.003～0.33 s^-1。计算结果表明,所有条件下制备的样品的活化能为125～139 k J/mol,应力指数为3.5～4.2,表明主要的热变形机制是位错蠕变,由位错攀移和溶质拖曳机制控制。材料常数n和Q取决于晶粒尺寸,第二相颗粒比例等微观结构因素,通过三维曲面曲线预测了二者的关系。此外,挤压后的ZK60板材具有相似的强基面织构,因此,合金在SPT过程中具有相同的变形机制与相近的n和Q值。     

经不同熔体处理的易拉罐用铝材的热压缩变形组织

采用动态热/力模拟实验技术对经不同熔体处理的易拉罐用铝材进行高温压缩变形实验,并用光学显微镜、透射电镜分析探讨其热变形组织特征。结果表明:冶金质量影响易拉罐用铝材的动态再结晶组织特征,在未处理或常规熔体处理状态下存在枝晶网胞结构,晶粒组织不均匀;高效熔体处理使易拉罐用铝材在较低的温度下即可通过亚晶合并方式发生动态再结晶,并在变形温度573~673 K、应变速率0.1~1.0 s-1、变形量约0.7的较宽的热变形工艺条件下可获得细小且分布较均匀的再结晶晶粒组织。     

On the rule-of-mixtures of the hardening parameters in TWIP-cored three-layer steel sheet

Although twinning-induced plasticity (TWIP) steels have high tensile strength with high strain hardening and large uniform elongation due to the formation of deformation twins during plastic deformation, sheet formabilities of TWIP steels are relatively poor. In this study, to overcome this problem, TWIP-cored three-layer architectured steel sheets are produced using cladding with low carbon steel sheaths. For an optimum design of layer architectured materials, strain hardening exponent n and strain rate sensitivity m of the layer sheets are theoretically and experimentally investigated. The forced-based rule-of-mixtures well reproduces the experimental values of the equivalent n and m. Contrary to the conventional rule-of-mixtures, the equivalent n and m of the TWIP-cored mild steel-sheath layered sheets are governed not only by volume fractions and n and m of parent materials but also by the strength of strong layer.     

Comparative study of the influence of various melt-treatment methods on hot deformation behavior of 3003 Al alloy

3003 Al alloy samples with various metallurgical qualities were obtained by various melt-treatment methods and were deformed by isothermal compression in the deformation temperature range of 300°C to 500°C at strain rates between 0.0l and 10.0 s⁻¹ with a Gleeble-1500 thermal simulator. The results show that there is a close relationship between melt-treatment and subsequent thermal deformation. The hot deformation activation energy (Q) bears a linear relationship with the inclusion content (H) of 3003 Al alloy prepared by various melt-treatment methods, that is Q = 35.62 H + 171.58. The activation energy of the 3003 Al alloy prepared by the highly efficient melt-treatment is the lowest (174.62 kJ·mol⁻¹), which is beneficial to the material hot plastic deformation. The critical strain of the 3003 Al alloy prepared by various melt-treatment methods is investigated through the work hardening rate. Finally, the critical conditions of the investigated alloy were determined to predict the occurrence of dynamic recrystallization.     

Flow softening and microstructural evolution of TC11 titanium alloy during hot deformation

Hot compression tests on samples of the TC11 (Ti–6.5Al–3.5Mo–1.5Zr–0.3Si) titanium alloy have been done within the temperatures of 750–950 °C and strain rate ranges of 0.1–10 s^?1 to 40–60% height reduction. The experimental results show that the flow stress behavior can be described by an exponential law for the deformation conditions. The hot deformation activation energy (Q) derived from the experimental data is 538 kJ mol^?1 with a strain rate sensitivity exponent (m) of 0.107. Optical microstructure evidence shows that dynamic recrystallization (DRX) takes place during the deformation process. Moreover, only α DRX grains are founded in the titanium alloys. The influences of hot working parameters on the flow stress behavior and microstructural features of TC11 alloy, especially on the type of phase present, the morphologies of the α phase, grain size and DRX are analyzed. The optimum parameters for hot working of TC11 alloy are developed.     

罐用铝材高温流变应力行为的研究

用热模拟试验方法对压力罐用铝材(简称"铝原块")进行热压缩变形,探讨了熔体处理和变形条件对该材料高温流变应力行为的影响.结果表明:经不同熔体处理的铝原块均存在稳态流变特征;应变速率达10.00s-1时,流变曲线上均出现峰值应力,即该材料出现了动态再结晶;稳态变形阶段的流变应力与应变速率或变形温度分别满足双曲正弦函数关系和Arrhenius关系;与未处理的、常规处理的铝原块相比,经高效熔体处理的铝原块的真应力值及进入稳态阶段所对应的真应变值均较小,热变形激活能也有较明显的降低;此外还求出经高效熔体处理的铝原块的高温流变应力方程.     

Characterization of hot deformation behavior of as-forged TiAl alloy

The deformation behavior of as-forged Ti–43Al–9V–Y alloy was investigated by hot compression tests in the temperature range of 1100–1225 °C and strain rate range of 0.01–0.5 s⁻¹. The results show that the alloy exhibits negative temperature sensitivity and positive strain rate sensitivity. The stress exponent (n = 3.02) and the apparent activation energy (Q = 342.27 kJ/mol) of the present alloy are lower than that of previous reported TiAl alloys, which suggests that the as-forged Ti–43Al–9V–Y alloy exhibits better deformability at low temperatures and high strain rates. A processing map for hot working was developed on the basis of a dynamic material model. The deformation mechanisms were analyzed by the processing map. The optimum processing condition at the strain of 0.6 is 1180–1210 °C/0.01–0.05 s⁻¹. A crack-free Ti–43Al–9V–Y sheet was prepared by hot rolling at these optimized parameters. EBSD results show that dynamic recrystallization is more likely to occur for γ phase.     

Constitutive modeling of hot deformation behavior of X20Cr13 martensitic stainless steel with strain effect

Hot deformation behavior of X20Cr13 martensitic stainless steel was investigated by conducting hot compression tests on Gleeble–1500D thermo-mechanical simulator at the temperature ranging from 1173 to 1423 K and the strain rate ranging from 0.001 to 10 s^?1. The material constants of α and n, activation energy Q and A were calculated as a function of strain by a fifth-order polynomial fit. Constitutive models incorporating deformation temperature, strain rate and strain were developed to model the hot deformation behavior of X20Cr13 martensitic stainless steel based on the Arrhenius equation. The predictable efficiency of the developed constitutive models of X20Cr13 martensitic stainless steel was analyzed by correlation coefficient and average absolute relative error which are 0.996 and 3.22%, respectively.     

Strain-rate sensitivity of powder metallurgy superalloys associated with steady-state DRX during hot compression process

Strain-rate sensitivity (SRS) is an important parameter to describe the thermodynamic behavior in plastic deformation process. In this research, the variation of SRS associated with steady-state DRX in P/M superalloys was quantitatively investigated. Based on the theoretical analysis and microstructural observation of the alloy after deformation, the SRS coefficient was employed to identify the deformation mechanism of the alloy. Meanwhile, the corresponding relationship between SRS coefficient m, stress exponent n and deformation mechanism was revealed. The stress exponent n in the Arrhenius constitutive model of P/M superalloys was calculated. In addition, it is found there is a relatively stable stress exponent range (n = 4-6), indicating that dislocation evolution played as the major hot deformation mechanism for P/M FGH4096 superalloy. Furthermore, the Bergstrom model and Senkov model were used and combined together to estimate the SRS coefficient in the steady-state DRX and the m value maintains at 0.2-0.22, which are consistent with the microstructural evolution during hot deformation process. The SRS coefficient distribution map and power dissipation efficiency distribution map were finally constructed associated with the microstructural evolution during hot deformation, which can be used to optimize the processing parameters of the superalloys.     

BEHAVIOR OF FLOW STRESS OF ALUMINUM SHEETS USED FOR PRESSURE CAN DURING COMPRESSION AT ELEVATED TEMPERATURE

The behavior of flow stress of Al sheets used for pressure can prepared by different melt-treatment during plastic deformation at elevated temperature was studied by isothermal compression test using Gleeble1500 dynamic hot-simulation testing machine. The results show that the AI sheets possess the remarkable characteristic of steady state flow stress when they are deformed in the temperature range of 350-500℃ at strain rates within the range of 0.01-10.0s^-1. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate, and an Arrhenius relationship with the temperature, which implies that the process of plastic deformation at elevated temperature for this material is thermally activated. Compared with the AI pieces prepared by no or conventional melt-treatment, hot deformation activation energy of AI sheets prepared by high-efficient melt-treatment is the smallest （ Q= 168.0kJ/mol）, which reveals that the hot working formability of this material is very better, and has directly to do with the effective improvement of its metallurgical quality.     

考虑应变补缩的6063铝合金高温流变应力本构方程(英文)

为了建立精确模拟6063铝合金高温流变应力的本构方程,在温度为573~773 K和应变速率为0.5~50 s-1的条件下,采用Gleeble-1500热模拟机进行等温热压缩实验。结果表明:可以采用参数Z描述温度和应变速率对6063铝合金热变形行为的影响,建立的本构方程中的材料常数(α,n,Q和A)可以表示成应变的4次多项式函数。模拟结果表明:所建立的本构方程能精确预测6063铝合金高温流变应力,因此,本构方程适合用于模拟热变形过程,如挤压和锻造,并且可以在工程应用中正确设计变形参数。     

Hot deformation behavior of Mg-7.22Gd-4.84Y-1.26Nd-0.58Zr magnesium alloy

The behavior evolvement of Mg-7.22Gd-4.84Y-1.26Nd-0.58Zr(GWN751K) magnesium alloy during the hot deformation process was discussed.The flow stress behavior of the magnesium alloy over the strain rate range of 0.002 to 2.000 s-1 and in the temperature range of 623 to 773 K was studied on a Gleeble-1500D hot simulator under the maximum deformation degree of 60%.The experimental results showed that the relationship between stress and strain was obviously affected by strain rate and deformation temperature.The flow stress of GWN751K magnesium alloy during high temperature deformation could be represented by the Zener-Hollomon parameter in the hyperbolic Arrhenius-type equation.The stress exponent n and deformation activation energy Q were evaluated by linear regression analysis.The stress exponent n was fitted to be 3.16.The hot deformation activation energy of the alloy during hot deformation was 230.03 kJ/mol.The microstructures of hot deformation were also influenced by strain rate and compression temperature strongly.It was found that the alloy could be extruded at 723 K with the mechanical properties of σ0.2 = 260 MPa,σb = 320 MPa,and δ = 18%.     

Effect of Hot Band Annealing on Forming Limit Diagrams of Ultra-Pure Ferritic Stainless Steel

In order to better understand the texture evolution, coincidence site lattice (CSL) and forming limit diagrams (FLDs) of ferritic stainless steels with and without hot band annealing, the texture evolution and CSL of ferritic stainless steels with 15% Cr content were studied by using x-ray diffraction and electron back-scattered diffraction technique. The strain hardening exponent n value, the strength coefficient K value, and Plastic strain ratio r value are the key parameters for the FLD. It was found out that the FLD_o of plane strain condition and the stretchability were mainly influenced by their n value and K value, respectively. The higher n value and K value, better was the stretchability of investigated steels. The intensity of the γ-fiber dominated by {111} 〈112〉 was improved significantly in the cold rolled and annealed sheets because of a hot band annealing treatment and the sharp increase of Σ13b CSL boundaries. The increase of the formability is attributed to the significantly increase of the r value.     

Influence of initial texture on formability of AZ31B magnesium alloy sheets at different temperatures

Repeated unidirectional bending (RUB) process was carried out to improve the texture of AZ31B magnesium alloy sheets. Influence of initial texture on formability of AZ31B magnesium alloy sheets at different temperatures was investigated. Compared with the as-received sheets, the limiting drawing ratio of the RUB processed sheets increased to 1.3 at room temperature, 1.5 at 50 °C and 1.7 at 100 °C, respectively. The improvement of the press formability at lower temperatures can be attributed to the texture modification, which led to a smaller Lankford value and a larger strain hardening exponent. However, the press formability of the sheet with a weakened basal texture has no advantage at higher temperature. This is due to much smaller r-value that results in severe thinning in thickness direction during the stamping process which is unfavorable to forming. Anyhow it is likely that the texture control has more effect on the press formability at lower temperature.     

Temperature-Dependent Flow Behavior and Microstructural Evolution During Compression of As-Cast Mg-7.7Al-0.4Zn

The microstructure and mechanical properties improve substantially by hot working. This aspect in as-cast Mg-7.7Al-0.4Zn (AZ80) alloy is investigated by compression tests over temperature range of 30-439°C and at strain rates of 5 × 10^?2, 10^?2, 5 × 10^?4 and 10^?4 s^?1. The stress exponent (n) and activation energy (Q) were evaluated and analyzed for high-temperature deformation along with the microstructures. Upon deformation to a true strain of 0.80, which corresponds to the pseudo-steady-state condition, n and Q were found to be 5 and 151 kJ/mol, respectively. This suggests the dislocation climb-controlled mechanism for deformation. Prior to attaining the pseudo-steady-state condition, the stress-strain curves of AZ80 Mg alloy exhibit flow hardening followed by flow softening depending on the test temperature and strain rate. The microstructures obtained upon deformation revealed dissolution of Mg₁₇Al₁₂ particles with concurrent grain growth of α-matrix. The parameters like strain rate sensitivity and activation energy were analyzed for describing the microstructure evolution also as a function of strain rate and temperature. This exhibited similar trend as seen for deformation per se. Thus, the mechanisms for deformation and microstructure evolution are suggested to be interdependent.     

Warm Temperature Deformation Behavior and Processing Maps of 5182 and 7075 Aluminum Alloy Sheets with Fine Grains

The tensile deformation behavior and processing maps of commercial 5182 and 7075 aluminum alloy sheets with similarly fine grain sizes (about 8 μm) were examined and compared over the temperature range of 423–723 K. The 5182 aluminum alloy with equiaxed grains exhibited larger strain rate sensitivity exponent (m) values than the 7075 aluminum alloy with elongated grains under most of the testing conditions. The fracture strain behaviors of the two alloys as a function of strain rate and temperature followed the trend in their m values. In the processing maps, the power dissipation parameter values of the 5182 aluminum alloy were larger than those of the 7075 aluminum alloy and the instability domains of the 5182 aluminum alloy were smaller compared to that of the 7075 aluminum alloy, implying that the 5182 aluminum alloy had a better hot workability than the 7075 aluminum alloy.     

3003铝合金热变形行为

采用不同熔体处理工艺获得3种不同冶金质量的3003铝合金,通过Gleeble-1500热模拟试验机对3003铝合金进行变形温度为300℃~500℃,应变速率为0.01s-1~10s-1高温等温压缩实验。结果表明,3003铝合金具有正的应变速率敏感性,热变形激活能Q与含杂量H呈线性关系,经高效综合处理的3003铝合金热变形激活能最低为174.62kJ.mol-1,有利于材料热塑性变形。采用加工硬化率计算不同熔体处理的3003铝合金的临界应变值,获得了经不同熔体处理的3003铝合金发生动态再结晶的临界条件。     

Mg-6Zn-1Al-0.3Mn 镁合金的热压缩变形行为及变形组织

采用Gleeble热模拟方法研究Mg?6Zn?1Al?0.3Mn 变形镁合金在温度为200~400°C,应变速率为0.01~7 s?1条件下的热压缩变形行为。结果表明,变形温度和应变速率显著影响其热变形行为。通过计算获得了热变形激活能及应力指数分别为Q=166 kJ/mol,n=5.99,且其本构方程为ε&=3.16×1013[sinh(0.010σ)]5.99exp [?1.66×105/(RT)]。热压缩显微组织观察表明：在应变速率为0.01~1 s?1的条件下,在250°C热压缩变形时初始晶粒晶界及孪晶处发生了部分动态再结晶,而在高温(350~400°C)条件下,发生了完全动态再结晶且再结晶晶粒尺寸随着应变速率的增加而减小。获得的较优的变形条件为温度330~400°C、应变速率为0.01~0.03 s?1以及350°C、应变速率为1 s?1。     

Constitutive modeling and understanding of the hot compressive deformation of Mg–9.5Zn–2.0Y magnesium alloy with reduced number of strain-dependent constitutive parameters

The hot compressive flow behavior of the cast Mg–9.5Zn–2.0Y alloy as a function of strain was analyzed, and the degree of dependence of the parameters (A: material constant, n ₂: stress exponent, Q _c: activation energy for plastic flow and α: stress multiplier) of the constitutive equation (\(\dot \varepsilon = A{\left[ {\sinh \left( {\alpha \sigma } \right)} \right]^{{n_2}}}\exp \left( {\frac{{ - {Q_c}}}{{RT}}} \right)\)) upon the strain was examined in a systematic manner. This is to explore the possibility of representing the hot compressive deformation behavior of metallic alloys in a simple way by using a reduced number of strain-dependent constitutive parameters. The analysis results for several different cases can be interpreted as follows: (1) Q _c can be treated as being strain-independent, which is physically sensible; (2) while only the microstructure changes as a function of strain at low flow stresses, as the flow stress increases, the power-law creep deformation and power-law breakdown mechanisms change; (3) the regime where only A is strain dependent expanded to higher strain rates and lower temperatures as the strain increased, suggesting that the number of the strain-dependent parameters decreases as the initial microstructure is refined by dynamic recrystallization, and the microstructure approaches a steady state.