压下率对泡沫铝夹层板制备的影响

以空气雾化的AlSi 12合金粉和TiH2粉末为原料,采用粉末包套轧制法成功制备出泡沫铝夹层板.通过对包套轧制进行了理论分析,结合SAYN-CG90数码相机、扫描电镜(SEM)和显微硬度仪等检测方法,系统研究了不同压下率对制备预制体的致密度和界面结合,以及泡沫铝夹层板泡孔结构的影响.结果表明:当压下率为70%的时候,可以获得表面平直、完整,粉体均匀、致密的预制坯,并且实现面板与芯层的有效结合,最终获得泡孔结构完整和均匀的泡沫铝三明治板.     

The effect of grain size, strain rate, and temperature on the mechanical behavior of commercial purity aluminum

Commercial purity aluminum AA1050 was subjected to equal channel angular extrusion (ECAE) that resulted in an ultrafine-grained (UFG) microstructure with an as-received grain size of 0.35 μm. This UFG material was then annealed to obtain microstructures with grain sizes ranging from 0.47 to 20 μm. Specimens were compressed at quasi-static, intermediate, and dynamic strain rates at temperatures of 77 and 298 K. The mechanical properties were found to vary significantly with grain size, strain rate, and temperature. Yield stress was found to increase with decreasing grain size, decreasing temperature, and increasing strain rate. The work hardening rate was seen to increase with increasing grain size, decreasing temperature, and increasing strain rate. The influence of strain rate and temperature is most significant in the smallest grain size specimens. The rate of work hardening is also influenced by strain rate, temperature, and grain size with negative rates of work hardening observed at 298 K and quasi-static strain rates in the smallest grain sizes and increasing rates of work hardening with increasing loading rate and grain size. Work hardening behavior is correlated with the substructural evolution of these specimens.     

The combined effect of grain size and strain rate on the dislocation substructures and mechanical properties in pure aluminum

The effect of grain size on the development of dislocation substructures has been studied as a function of strain rate. Pure aluminum rods with grain diameters of 70, 278, and 400 μm were deformed in tension at room temperature to various percent strains at strain rates of 0.01, 0.25, 2.5, and 5/min. It has been confirmed that the smaller grain size results in higher flow stress in this strain-rate range. The cell size strengthening described by the modified Hall-Petch (MHP) equation is applicable to samples with 70 and 278 μm grain sizes at all four strain rates used in this study, while 400 μm grain sizes show deviation from this because of inhomogeneities developed in the microstructure. The influence of strain rate on the slope of the MHP plots, for a grain size of 70 μm, is such that at lower strain rates, the slope does not change much, but at higher strain rates, there is an increase in the slope value. At all strain rates, the values of slopes from the MHP plots of the smaller grains are higher than for the larger grains.     

The effect of grain size and strain rate on the

The substructural developments taking place in nickel 200 with grain diameters of 47, 108, 141, and 274 μm have been studied at four different strain rates of 0.01, 0.25, 2.5, and 5/min during tensile testing at room temperature. The percent strain necessary to develop well-defined cell boundaries increases with an increase in grain size at a given strain rate. The cell size refinement takes place throughout the entire range of percent strains (up to 30 pct) in tension for the nickel samples with grain diameters of 47, 108, and 141 μm at all four strain rates used in this article. However, nickel, with the largest grain diameter of 274 μm, shows refinement and then sat- uration for tensile strains greater than 25 pct. The cell size strengthening described by the mod- ified Hall-Petch (MHP) equation at the selected four strain rates of this article indicates that the flow stress is higher for smaller grain size samples at a given cell size. The effect of strain rate on the slope from the MHP plots is such that even though it does not change with an increase in strain rate up to 0.25/min for the four grain sizes, the actual value of the slope decreases with an increase in grain size at a given strain rate. Beyond this strain rate, even though an increase in the slope value as a function of strain rate has been observed for all four grain diameter samples, the influence of grain size on the slope of the MHP plots is so small that it can be assumed that they may become grain size independent at extremely high strain rates. JYOTHI G. RAO, formerly Graduate Student, JYOTHI G. RAO, formerly Graduate Student, JYOTHI G. RAO, formerly Graduate Student,     

The effect of strain rate on the cyclic response of metals

Monotonie and cyclic strain hardening parameters were measured for five alloys: 7075-T6 aluminum; 6061-T651 aluminum, an α/β brass (alloy 365); copper-l. pct beryllium (alloy 172); and martensitic 4340E steel. Cyclic measurements were made under fully reversed strain control at constant strain rate. A maximum strain of ±0.015 and strain rates of 0.003, 0.03, 0.10, and 0.30 s^-1 were used. The cyclic stress-strain coefficientsK’ and exponentsn’ were found to be independent of strain rate and had the values: 7075-T6 (105 ksi, 0.06); 6061-T651 (60 ksi, 0.06); brass (132 ksi, 0.21); copper-beryllium (165 ksi, 0.13); 4340E steel (300 ksi, 0.19). Adiabatic heating imposed an upper limit < 0.3 s^-1) on the strain rate at which isothermal cyclic strain hardening tests could be performed. Formerly with Midwest Research Institute     

Strain hardening at high strain in aluminum alloys and its effect on strain localization

The modes of strain localization in the tensile testing of a sheet sample are diffuse necking, localized necking and, in some materials, localization in an unstable shear band. In a tensile test of a rate insensitive material, the normalized strain hardening parameter,H = (1/σ)(dσ/dε) has the values ofH = 1 for diffuse necking andH = 0.5 for localized necking. Curves ofH vs strain were obtained up to large values of plastic strain using the hydraulic bulge test. The materials selected were commercially important sheet alloys in the condition normally used for forming. It is shown that the materials have similarH vs strain curves in the range of uniform tensile straining, but the curves diverge widely at higher strains whereH falls below 1. This has important consequences on strain localization behavior. The limit strains of the alloys in simple tension and punch stretching show reasonable correlation with their values ofH and those alloys which are susceptible to catastrophic shear failure have low values ofH at high strains. Strain rate sensitivity adds to or subtracts from theH values obtained in this study and has an additional influence on strain localization. Formerly with Alcoa Laboratories, Alcoa Center, PA 15069, U.S.A     

泡沫铝材料的研究与应用

泡沫金属具有实体金属不具备的热、声、轻质、能量吸收等优异性能,成为一种新型结构功能材料.被誉为"金属明星"的多孔泡沫铝材料是目前研究最为热门、最具应用潜力的泡沫金属,具有密度小、耐高温、抗腐蚀、不易燃、耐候性好、导热率低、电磁屏蔽强、吸能降噪等优异性能,被广泛应用在汽车工业、航空航天、建筑工业等工程领域.本文综述了泡沫...     

The large strain deformation of some aluminum alloys

The stress-strain behavior of both non-heat-treatable and heat-treatable aluminum alloys has been examined over a large strain range by a variety of deformation modes. In superpurity aluminum deformed in torsion, the work hardening rate approaches zero at strains of four to five, while a definite saturation in the flow stress is observed at much lower strains in the precipitation hardened alloys. In the non-heat-treatable alloys, a saturation in the flow stress is not approached at even very large strains. Nevertheless, the stress-strain behavior of all the alloys can be reasonably represented by a saturation type stress-strain equation. The deformation behavior of the alloys can be qualitatively understood in terms of the dislocation accumulation processes and slip morphology in the different alloys. Finally, it is shown that alloys deformed on a commercial rolling mill exhibit equivalent stress-strain behavior to that found in these laboratory deformation studies.     

The continuity of plastic strain rate

The question of plastic strain rate continuity during instantaneous changes in total strain rate is addressed. This issue has important implications for models of plastic deformation kinetics. The particular case of a total strain rate change represented by the start of a stress relaxation test is considered in detail. It is concluded from a theoretical analysis that extreme experimental precision is required to detect plastic strain rate continuity at the start of stress relaxation. It is shown that the degree of experimental precision required depends on both material and experimental variables. Supporting experiments confirm plastic strain rate continuity in aluminum, iron and 304SS.     

粉末烧结法制备开孔泡沫铝压缩性能的研究

采用粉末烧结工艺制备开孔泡沫铝并研究了其压缩性能，不同形态的尿素和氯化钠颗粒作为造孔剂使泡沫铝的孔隙度控制在70％。结果表明：粉末烧结法制备的泡沫铝呵以容易地控制孔隙度及孔径的大小，并且孔结构很好地保持了造孔剂的形状。不同的孔结构对泡沫铝的压缩性能具有显著影响，球形孔结构得到了最佳的压缩效果。     

The tensile stress diagram assuming an elastic hyperbolic sine strain rate law

The tensile stress-strain relations are considered in the microstrain region assuming that there exists an anelastic strain whose strain rate dependence varies as the hyperbolic sine of the relaxable strain. The equations giving the stress-strain curves for the cases of loading, unloading, and reloading are derived. The equations are compared with experimental curves obtained using zirconium specimens prestrained at 77°K to obtain an anelastic strain component.     

泡沫铝制备过程中增粘剂的选择

研究了铝熔体中添加不同种类增粘剂后的增粘效果,并通过对制备泡沫体的宏观观测和微观检测,研究了铝熔体增粘方式对泡沫体结构的影响及各种增粘剂的增粘机理. 结果表明:铝熔体中加入金属钙、镁、氧化铝和粉煤灰后,其物相组成发生改变,增粘剂存在形式和增粘机理不同,得到的泡沫体在结构上差别也很大.     

泡沫铝及其复合材料的研究进展

泡沫金属是一种由金属基体和气孔组成的新型结构功能材料,相对于实体金属材料,泡沫金属材料以牺牲了强度等力学性能为代价,获得了诸如热、声、能量吸收、轻质等优越性能,成为一种新型结构功能材料。泡沫铝是一种在铝基体中形成很多气孔的轻质多孔金属材料,同时兼有金属和气泡特征,它密度小、耐高温、防火性能强、抗腐蚀、隔音降噪、导热率低、电磁屏蔽性高、耐候性强、有过滤能力、渗透性好,具有良好的阻尼特性和电磁屏蔽能力,广泛应用在冶金、化工、航空航天、船舶、电子、汽车制造和建筑业等领域。对泡沫铝制备方法和物理性能的研究有利于提高其性能、扩大其应用领域,本文概述了泡沫铝的制备方法、物理性能及增强泡沫铝基复合材料的研究进展。     

Effect of strain and strain rate on the bauschinger effect response of three different steels

The Bauschinger behavior after a strain reversal was evaluated for samples with microstructures representative of production sheets for a low-carbon (LC) steel, a high-strength low-alloy (HSLA) steel, and a dual-phase (DP) steel. The microstructures were produced in the samples by laboratory hot rolling and heat treatment. Bauschinger tests were run at strain rates of 0.0001, 0.001, and 0.01 s⁻¹, with tensile prestrains between 1 and 7 pct. After the reversal, the samples were strained 2 pct in compression. The Bauschinger effect is described by a Bauschinger effect parameter (BE), which is the difference between the steel strength at reversal and the 0.05 pct offset yield strength on the reversal, normalized by the steel strength at reversal. It is found that the Bauschinger effect is a continuous increasing function of the strength of the steel, provided the steel is prestrained at least 2.5 pct or beyond the yield point elongation. A single trend line describes the Bauschinger effect variation with steel strength, for all three steels in the present study and for an aluminum-killed drawing quality (AKDQ) steel from a previous investigation. No strain rate influence on the BE was found, due to the limited strain rate range and data uncertainty.     

The effect of cooling rate from the melt on the recrystallization behavior of aluminum alloy 6013

In most commercial operations, the plant metallurgist likely has little control over the solidification rate of the process. However, solidification rate is affected by the dimensions of the ingot, and product form (plate ingot vs extrusion billet, for example) determines the dimensions of the ingot to be cast. Consequently, understanding the effects of solidification rate might be useful in explaining differences in microstructure that are often observed in various product forms cast from equivalent compositions. To provide this microstructural information, the effect of cooling rate from the melt on the microstructural changes in hot-rolled and solution heat treated (SHT) aluminum alloy 6013 was investigated. The range of cooling rates in this investigation is comparable to what might be observed through the thickness of a plate ingot. Over the cooling rate range investigated (0.5 to 5 K/s), recrystallization behavior of the alloy appears to be primarily affected by the size and number density of the coarse α(AlFeMnSi) constituent particles, which act as sites for particle stimulated nucleation (PSN) of recrystallized grains. At intermediate cooling rates (1.5 K/s), the resistance to recrystallization is at a minimum. As the cooling rate increases beyond 1.5 K/s, the number of particles available for PSN decreases; thus, there is a decrease in the fraction of recrystallized grains after heat treating. On the other hand, as the cooling rate is decreased from 1.5 K/s, the size of the constituents increases; however, their number decreases, once again leading to a decrease in the fraction of recrystallized grains observed after heat treatment.