Growth behavior of hydrogen micropores in aluminum alloys during high-temperature exposure

X-ray microtomography was used to observe hydrogen micropores and their growth behavior at high temperatures in several aluminum alloys. High-density micropores were observed in high-purity Al–Mg alloys, but their density and volume fraction were much lower in pure aluminum. Our results have revealed that the growth behavior of micropores is dominated by Ostwald ripening. About 53% of hydrogen is trapped in micropores in Al–Mg alloy with low hydrogen content, making micropores the predominant hydrogen trap site. Although total hydrogen content is similar to that in the alloy, the ratio of hydrogen trapped in micropores is below 7% in pure aluminum. This difference is attributable to the lack of hydrogen precipitation sites in pure aluminium. Although the overall amounts of hydrogen at dislocations and grain boundaries are small in all the materials, the occupancies for these trap sites were concluded to be very high.     

Phase-stability dependence of plastic deformation behavior in Ti-Nb-Ta-Zr-O alloys

The authors investigated the effects of alloy content on mechanical properties to make clear a correlation between plastic deformation behavior and β-phase stability in Ti-Nb-Ta-Zr-O alloys. It was realized that there was specific compositional area in which the alloy exhibited little work hardening and minimum Young’s modulus value. The specific area was expressed by the bond order (Bo), based on theDV-Xα method, of 2.87 and the averaged electron/atom ratio (e/a) of 4.24, which corresponded to those of a multifunctional β titanium alloy, “Gum Metal.” These electronic conditions also minimized ideal strength required for plastic deformation without any dislocation activity. The deformation behavior of alloys in the specific compositional area revealed that the unique behavior could be characterized by a “giant fault.” It was also confirmed that such a compositional area corresponded to the phase boundary between the α″ martensite and β phases at room temperature. This paper was presented at the Beta Titanium Alloys of the 00’s Symposium sponsored by the Titanium Committee of TMS, held during the 2005 TMS Annual Meeting & Exhibition, February 13–16, 2005 in San Francisco, CA.     

Al-Zn-Mg-Cu-Zr铝合金的高温热压缩变形行为(英文)

在温度为300-450°C和应变速率为0.01-10s-1的变形条件下,对Al-Zn-Mg-Cu-Zr合金(7056和7150铝合金)进行热压缩实验。结果表明:在一定的应变峰值出现后,流动应力随应变增加单调下降,呈现出流动软化。峰值应力取决于温度补偿应变速率Z的大小,可用包含Zener-Hollomon参数的双曲正弦关系来描述合金热流变行为。7056合金的变形激活能为244.64kJ/mol,而7150合金的为229.75kJ/mol;在同样的变形条件下,前者的峰值应力却低于后者。在高Z值条件下,在延长晶粒的亚晶粒中存在大量析出物;而在低Z值条件下,再结晶化的晶粒内出现完整的亚晶。7150合金中存在细小亚晶和大量析出物,由于亚结构强化和析出硬化造成其峰值应力比7056合金高。     

6061铝合金高温流变行为

利用Gleeble-3500热模拟实验机,对6061铝合金在变形温度为350℃、400℃、430℃、460℃、480℃和500℃,应变速率为0.001s-1、0.01s-1、0.1s-1、1s-1和10s-1条件下进行高温压缩实验,得到的真应力-真应变曲线形态基本符合铝合金的热变形力学特征。采用Arrhenius双曲正弦关系描述6061铝合金的高温流变行为,确定其激活能Q=163.4366kJ·mol-1;基于动态材料模型理论绘制6061铝合金热加工图,确定其最佳热加工区域温度为T=420℃~450℃。     

Mechanisms of grain refinement in aluminum alloys in the process of severe plastic deformation

A study of the mechanisms of grain refinement in the process of severe plastic deformation of two aluminum alloys, i.e., 2219 bearing nanometric particles of Al₃Zr and low-alloy Al-3% Cu, is described. The alloys are deformed by the method of equal channel angular pressing at 250°C to a maximum strain degree of about 12. The angles of (sub)grain boundaries in alloy 2219 are determined with the help of transmission electron microscopy by the method of Kikuchi lines. The evolution of the microstructure in alloy Al-3% Cu is studied with the help of grain-boundary maps obtained by the method of electron back-scattered diffraction. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 14–19, February, 2006.     

2E12铝合金的高温塑性变形流变应力行为

通过在Gleeble-l500热模拟试验机上进行等温热压缩试验,研究2E12铝合金在变形温度为300～500℃和应变速率为0.0l～l0 s-1条件下的流变应力行为,计算、推导出用包含Arrhenius项的Zener-Hollomon参数描述2E12合金高温压缩流变行为的表达式,并分析形变热、变形温度和应变速率等参数对流变应力的影响规律。结果表明:应变速率和变形温度对2E12合金的流变应力影响显著,流变应力随着温度的升高而降低,随着应变速率的提高而增大;在ε≥1 s-1时,形变热导致流变应力降低,且幅度随着应变速率的增大而增大,随着变形温度的升高而降低。     

Particle cracking and rotation during plastic deformation of 7075 aluminum alloy

The utility of a novel digital image processing technique for automatic detection and separation of cracked constituent particles was applied to quantitatively characterize the microstructural damage on Fe-rich intermetallic particles that were cracked in a 7075 Al-alloy. This cracking of the Fe-rich intermetallic particles was due to a function of strain under uniaxial tension, compression, and torsion. The comparison of the data on the strained samples revealed that at tensile strain, the number fraction of the cracked Fe-rich particles was significantly higher than those at torsion while the compression strains and the average volume of the cracked Fe-rich particles increased when the strain increased. The percentage-cracked particles had a linear relationship with all of the strains for all of the loading conditions. Significant rotations of Fe-rich intermetallic particles occurred during the deformation of this alloy under torsion. These rotations tended to align themselves along the direction of applied/induced tensile stretch, which in turn affected the progression of damage due to particle cracking.     

On the evolution of surface roughness during deformation of polycrystalline aluminum alloys

Surface roughening of polycrystalline Al–Mg alloys during tensile deformation is investigated using white light confocal microscopy. Materials are tested that differ only in grain size. A height–height correlation technique is used to analyze the data. The surface obeys self-affine scaling on length scales up to a correlation length which approximately equals the grain size and above which no height correlation is present. The self-affine scaling exponent increases initially with strain and saturates at a value around 0.9. A linear relation is observed between root-mean-square roughness and both strain and grain size. The observed roughness is explained as the result of the combined effect of a self-affine roughening on a subgrain scale and a grain scale roughening caused by orientation differences between neighboring grains.     

Elevated-temperature coarsening behavior in aluminum alloys

Coarsening kinetics of the equilibrium phase in the Al- rich end of the Al- Ti- Cu and Al- Ti- Ni systems have been studied using transmission electron microscopy as a function of annealing times at 698 K. The equilibrium phase in the Al- Ti- Ni system coarsens at a rate that is 6 times faster than that in the Al- Ti- Ni phase. This difference in the coarsening kinetics is related to the amount of mismatch of each of the equilibrium phases with respect to the Al- matrix.     

Forced chemical mixing in immiscible alloys during severe plastic deformation at elevated temperatures

The forced chemical mixing of atoms in model immiscible alloys during severe plastic deformation (SPD) has been investigated as a function of temperature and the heat of mixing using molecular dynamics computer simulations. At low temperatures, A₇₅B₂₅ alloys form solid solutions during SPD for heats of mixing less than ～20 kJ mol^?1, but tend to phase separate at larger values. At high temperatures these alloys show more extensive precipitation, with the precipitate morphology dependent on the heat of mixing. Analysis of the high-temperature mixing kinetics reveals that the precipitation process involves two separate mechanisms. The first derives from long-range diffusion mediated by shear-induced vacancies, while the second is due to local rearrangements of atoms induced by the forced mixing of atoms.     

铝合金板在循环塑性变形下的韧性断裂行为模拟(英文)

基于数值模拟的方法研究在循环塑性变形下铝合金板的力学行为。首先,通过Cockcroft-Latham韧性断裂准则得到材料的断裂极限应力图,并通过实验对成形极限应力图进行验证。数值模拟结果表明:滚边时弯曲中心的应变路径可以认为是平面应变状态;采用绳式滚边方法可以改善在弯曲中心线上的应力集中现象。从滚边断口的扫描电镜照片可以发现,循环塑性变形对铝合金板的韧性断裂行为有影响。     

高温变形条件下5A02铝合金的塑性成形性能

随着工业技术的发展和能源问题的突出,铝合金以其质量轻、耐腐蚀性能好、成形性能和加工性能良好等优势成为轻型化首选的材料类型之一。以5A02铝合金冷轧板材为研究对象,通过单向拉伸试验和金相试验对不同变形温度、应变速率条件下5A02铝合金的塑性性能进行分析,并且借助试验数据和Zener-Hollomo参数模型,对高温条件下5A02铝合金的本构模型进行研究。研究结果表明：5A02铝合金在高温条件下变形时,应变速率和变形温度对延伸率的影响很大。在应变速率为0.01s-1、0.001 s-1、0.0005 s-1和0.0001 s-1条件下,当变形温度大于250℃时,5A02铝合金的延伸率大于100%。当变形温度为150℃~250℃时,5A02铝合金的真实应力-应变曲线属于动态回复型,而当变形温度大于250℃时,流变应力曲线存在明显的软化现象。     

大塑性变形6013铝合金的时效特性与力学性能

利用X射线衍射分析（XRD）、差示扫描量热法（DSC）和拉伸试验,研究不同温度等通道转角挤压（ECAP）和常规静态时效处理后6013 Al-Mg-Si铝合金的微观结构、时效行为、析出动力学以及力学性能。XRD测得的ECAP变形后合金的平均晶粒尺寸在66-112 nm范围内,平均位错密度在1.20×10^14-1.70×10^14 m^-2范围内。DSC分析表明,由于ECAP后试样比常规时效处理试样拥有更细小的晶粒和更高的位错密度,因此,ECAP变形后合金的析出动力学更快。与未变形合金相比,ECAP后试样的屈服强度和抗拉强度都得到了显著提高。室温ECAP后试样的强度达到最大,其屈服强度是静态峰时效屈服强度的1.6倍。细晶强化、位错强化以及由于ECAP过程中的动态析出而产生的析出相强化,是ECAP合金获得高强度的几种主要强化机制。     

Earing behavior and crystallographic texture of aluminum alloys during cold rolling

Earing behavior and crystallographic texture during cold rolling have been investigated for two commercial can body aluminum alloys. It is found that earing behavior can be inferred from texture information. The recrystallization texture causes 90° earing, while the deformation texture results in 45° earing. A strong recrystallization texture (or a high 90° earing) of a hot band causes a later appearance of lower 45° earing in the final gauge sheet and thus is desirable for industry. The earing behavior is better indicated by the delta function, which is characterized as the intensity difference between the deformation texture and the softening texture. The results indicate that the earing behavior during cold rolling can be quantitatively monitored by the crystallographic texture. In addition, effects of the texture inhomogeneity through-thickness have also been investigated and discussed.     

Ductile fracture behavior of 5052 aluminum alloy sheet under cyclic plastic deformation at room temperature

Ductile fracture behavior of a 5052 aluminum alloy sheet undergoing cyclic plastic deformation is investigated in order to clarify the effect of cyclic plastic deformation on formability enhancement in incremental stretch sheet forming at room temperature. In the incremental forming, formability markedly increases owing to strain distribution and accumulation effects. The former effect is activated when the deformation region expands along tool paths. Thus, localization of deformation, which leads to necking or fracturing, can be prevented. On the other hand, local strain is accumulated without fracturing when a blank sheet is repeatedly subjected to out-of-plane deformation at the same position. In this paper, the effect of the strain accumulation due to cyclic deformation generated by bending and unbending is primarily focused on to discuss the effect on deformability. To apply cyclic plastic straining to the specimen, a cyclic stretch-bending test was adopted. A cyclic tensile test was also conducted for larger bending curvature. The experimental results show that cyclic bending–unbending affects the ductility of sheet metals. The fractography obtained by scanning electric microscopy also indicates that fewer and smaller voids are observed particularly on bending the inner side than on the outer side.     

大塑性变形制备超细晶粒铝及铝合金材料

结合目前国内外大塑性变形制备超细晶粒材料的现状,重点阐述了累积轧制、高压扭转和等通道挤压等具有实际生产意义的制取超细晶粒铝及铝合金材料的技术,分析了这些制备超细晶粒铝及铝合金材料技术细化晶粒的机制;展望了大塑性变形制取超细晶粒铝及铝合金材料的发展前景.     

强塑性变形中Al-Cu二元合金相的溶解行为

研究了不同变形特性的Al-Cu合金相在等通道挤压(ECAP)和多向压缩(MAC)强塑性变形中的溶解行为.结果表明:可变形粒子θ′′和θ′在强变形中由于自身的应变,产生了具有高能量的亚晶界和剪切变形带,导致溶解发生,且由于表面能的作用使溶解持续进行;而对于难变形的θ粒子而言,只有破碎后的尖锐菱角部分由于表面能的作用而发生溶解;相对纯剪切应力的ECAP方法,MAC方法由于压应力分量的作用能够在析出相内部更有效地引入应变能,从而加速其溶解.     

摩擦条件对铝合金挤压变形流动行为的影响

通过有限元模拟和实验,对不同摩擦挤压过程中铝合金变形流动行为的机理进行分析,并利用罗德系数和应力偏量不变量(J2)等特征量进行变形分区.结果表明:采用积极摩擦可使挤压时的"死区"缺陷完全消失,且塑性区内材料的应变类型由3种变为均一的拉伸类变化,显著地提高了挤压过程中坏料横断面上金属流速的均匀性,更利于金属的挤出成形.