Tensile properties of some copper- and zinc-based alloys: Effects of strain rate and test temperature

This study analyzes the effects of test temperature and strain rate on the tensile properties of some copper-and zinc-based alloys. The copper-based alloys comprised a leaded-tin and an aluminum bronze, whereas the zinc-based alloys were added with various quantities of aluminum. The aluminum bronze attained maximum room-temperature tensile strength, whereas that of the leaded-tin bronze was the least. Among the zinc-based alloys, the one comprising 27.5 mass% aluminum exhibited superior tensile strength, followed by those alloyed with 11.5, 37.5, and 47.5 mass% aluminum in a descending order. Increasing strain rate tended to improve the tensile strength of the alloys. Tensile strength was reduced with an increase in test temperature irrespective of the alloy composition. The aluminum bronze possessed maximum strength regardless of temperature. The leaded-tin bronze attained least strength property at low temperatures, whereas higher test temperatures led to superior strength than the zinc-based alloys. The temperature sensitivity of the strength of the zinc-based alloys decreased with their aluminum content. Tensile elongation of the alloys tended to increase with an increase in strain rate and test temperature. Leaded-tin bronze was least affected in either case. The alloy also attained least elongation irrespective of test conditions. The aluminum bronze showed maximum elongation, at least at high strain rates. In the case of the zinc-based alloys, intermediate range of aluminum concentration led to better elongation. The elongation property of the alloys was affected by temperature in different manners. In a few cases, the elongation initially increased followed by a reduction beyond a specific test temperature, whereas, in other cases, a continuous increase with temperature was noted. The observations made have been discussed in terms of the nature of different microconstituents of the alloys whose effectiveness changes with test conditions. The response of the samples has been further substantiated with their fractographic features and subsurface characteristics.     

Superplastic-like behavior of Al-high Si alloys produced from rapidly solidified powders and ribbons

The high temperature tensile properties of hyper-eutectic Al-Si alloys were studied at temperatures between 683 and 813 K at initial strain rates between 8.3X10⁻⁴ and 4.2X10⁻¹s⁻¹. The alloys were prepared from prealloyed powders and ribbons, which were respectively fabricated by the centrifugal atomization and melt spinning, through the hot extrusion process at an extrusion ratio of 110:1. The extruded alloy bars prepared from the powders and ribbons, i.e. the powder-extruded and ribbon-extruded bars, have homogenous micro-structures with the fine silicon particles dispersed in the aluminum matrices for the Al-25Si and Al-15Si alloys. The maximum elongation-to-failure of the powder-extruded bar and the ribbon-bar are almost equal, 150%, for the Al-25Si alloy, In the Al-15Si alloy, the ribbon-extruded bar has superior elongation compared to the powder-extruded bar, that is, these are respectively 520% and 400%. The maximum elongation was attained at the relatively high strain rate of 10⁻²s⁻¹ independent of the silicon content and solidification process.     

Formation of nano-sized grains in Cu and Cu−Fe−P alloys by accumulative roll bonding process

Mechanical properties and formation of nano-sized grains in Cu and Cu−Fe−P alloys by the accumulative roll bonding (ARB) process were investigated. Nano-sized grains were successfully obtained in OFC and PMC-90 alloys by the ARB process after the third cycle. Once the 200 nm grains formed, further reduction in the grain size was not observed up to 8 ARB process cycles. For both alloys, the tensile strength values increased drastically in the initial stage of the ARB process. The tensile strength values of both alloys tended to saturate after the third ARB process cycle. The tensile elongation value greatly decreased by 1 cycle of the ARB process due to the strain hardening. After the third cycle of the ARB process, each alloy showed a gradual increase in tensile elongation due to the dynamic recovery. For PMC-90 alloy, the strength value was higher than that of OFC due to addition of the alloying elements. With increased annealing temperature, the nanosized grains tended to grow in OFC at 150°C, and after annealing at 200°C, coarse grains formed. On the other hand, in PMC-90 alloy, there was no grain growth up to 250°C due to the alloying elements (Fe, P).     

热处理对选区激光熔化GH3536合金晶界与拉伸行为的影响

采用选区激光熔化制备了GH3536合金,并分别进行固溶处理和热等静压处理,研究不同热处理手段对GH3536合金的组织形貌、晶界形态及室温拉伸行为的影响。结果表明:沉积态试样的组织由超细柱状亚晶粒与熔池界组成,存在气孔与微裂纹等缺陷;选区激光熔化试样分别经固溶处理和热等静压处理后,二者致密度均上升,组织转变为由交替分布的大小不等等轴晶粒组成,但热等静压的沿晶界析出M_(23)C_6相,形成锯齿状的弯曲晶界;沉积态试样的拉伸性能表现出各向异性的特点,固溶处理可消除拉伸性能的各向异性,但抗拉强度和屈服强度均有下降,延伸率明显上升。热等静压态试样与固溶态试样相类似,但其抗拉强度、屈服强度和延伸率均有进一步的提高;3种形态合金的断裂机制均为微孔聚集型的韧性断裂。     

快速凝固Cu-5Ag-0.5Zr-0.4Cr-0.35Nb合金的组织与力学性能

采用快速凝固方法制备了Cu-5Ag-0.5Zr及Cu-5Ag-0.5Zr-0.4Cr-0.35Nb(wt%)合金粉末,采用热等静压将粉末压制成坯料,随后进行热锻、冷轧处理。测试了合金在室温及高温(500 ℃)下的力学性能,并分析了合金的显微组织及断口形貌。结果表明,冷轧态合金具有更优异的室温拉伸性能,冷轧态Cu-Ag-Zr合金抗拉强度为739.3 MPa,伸长率7.1%,这与铜基体中密集的Cu₄AgZr颗粒及纳米级Ag颗粒有关。除Cu₄AgZr颗粒及Ag颗粒外,Cr、Nb元素的添加还生成高温稳定的Cr₂Nb颗粒,同时提高了合金的室温和500 ℃拉伸强度。冷轧态Cu-Ag-Zr-Cr-Nb合金的室温极限抗拉强度和伸长率分别为799.1 MPa与5.3%。因为热锻态合金晶粒尺寸粗大,Ag颗粒尺寸细小,相比冷轧态合金拥有更好的抗高温弱化性能。热锻态Cu-Ag-Zr-Cr-Nb和Cu-Ag-Zr合金的500 ℃抗拉强度分别为186.8和129.2 MPa,而冷轧态Cu-Ag-Zr-Cr-Nb和Cu-Ag-Zr合金在500 ℃抗拉强度分别仅为113.1和95.4 MPa。     

B含量对FeCrCoNiMn高熵合金组织及力学性能的影响

采用真空电弧熔炼炉制备了FeCrCoNiMnBx高熵合金,并对其微观组织和力学性能进行测试。未加入B元素时,合金组织具有单一FCC结构的胞状晶。B含量≥0.05时(at%),组织由FCC结构和具有树枝状和纳米颗粒状(Cr,Fe)₂B组成。随B含量的增加,合金的抗拉强度逐渐增加,硼含量为0.2(at%)时,合金的抗拉强度达到最大值610 MPa,但延伸率只有7%。B含量为0.1时,合金的综合力学性能最佳,抗拉强度为550MPa,延伸率为20%。故加入适量的B元素能提高高熵合金综合力学性能。     

Microstructural Characteristic and Mechanical Behavior of Nodular Silicon Hypereutectic Al-Si Alloys

The microstructure and mechanical properties of Al-Si-Cu-Mg alloys containing 12 wt.% to 30 wt.% Si are discussed. The eutectic and primary silicon particles are nodulized by a designed modification practice followed by a solution heat treatment of 6 h to 8 h at 510°C to 520°C. Metallographic analysis was used to measure structural characteristics of the Si-rich structures. Spheroidization of silicon phase leads to an increase in tensile strength and ductility of alloys at room temperature and 300°C compared with commercial Al-Si alloy. Increasing Si concentration causes the ultimate tensile strength and elongation at room temperature to fall due to the appearance of coarse silicon particles, but the ultimate tensile strength at 300°C remains unchanged.     

等轴细晶Ti-45Al-7Nb合金的高温机械性能及变形机制

采用粉末冶金法制备了双相等轴细晶Ti-45Al-7Nb（原子分数）合金,研究了该合金在温度为900、950和1000 ℃以及应变速率为1×10^-3、1×10^-4和5×10^-5 s^-1条件下的高温力学性能,并讨论了相应的变形机理。结果表明,在高温或低应变率下,Ti-45Al-7Nb合金的极限拉伸强度逐渐降低,但伸长率显著增加。由于细小晶粒容易实现变形和协调,其伸长率明显高于粗晶粒合金。高温拉伸后,合金在裂缝处形成大量的空洞,并在裂缝前部形成大量垂直于拉伸方向的长裂纹。此外,晶界的滑动、晶粒的孪生和动态再结晶也导致了合金变形,从而提高了微观组织的延展性。     

Superplastic Behavior of Copper-Modified 5083 Aluminum Alloy

An AA5083 aluminum alloy was modified with two different levels of Cu additions, cast by direct-chill method, and thermo-mechanically processed to sheet gauge. Copper additions reduced sheet grain size, decreased tensile flow stress and significantly increased tensile elongation under most elevated temperature test conditions. The high-Cu (0.8 wt.%) alloy had the finest grain size 5.3 μm, a peak strain-rate sensitivity of 0.6 at a strain-rate of 1 × 10⁻² s⁻¹, and tensile elongation values between 259 and 584% over the temperature range, 400-525 °C, and the strain rate range, 5 × 10⁻⁴ to 1 × 10⁻² s⁻¹, investigated. In biaxial pan forming tests, only the Cu-containing alloys successfully formed pans at the higher strain rate 10⁻² s⁻¹. The high-Cu alloy showed the least die-entry thinning. Comparison of ambient temperature mechanical properties in O-temper state showed the high-Cu alloy to have significantly higher yield strength, ultimate strength, and ductility compared to the base 5083 alloy. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6-9, 2005.     

热轧温度对低密度Nb-Ti-Al-V-Zr-C合金性能的影响

对经挤压开坯的一种低密度铌合金分别在1000,1100,1200℃下进行了热轧,并利用光学显微镜、扫描电镜和场发射透射显微镜对试样的组织形貌进行了表征;对合金的室温和高温拉伸强度、延伸率进行了测试。结果表明:在1200和1100℃温度下热轧时,合金均具有优良的室温和高温性能,室温强度在600MPa以上,室温塑性大于12%,高温下的强度在80MPa以上,高温塑性大于30%,且随轧制温度升高,抗拉强度降低,塑性增大;而在1000℃下热轧时,室温和高温力学性能均较低,且室温拉伸断口表现为脆性断裂。     

Tensile response of an Fe–40Al–0.7C–0.5B alloy

The uniaxial tensile properties of a B2 Fe–40Al based alloy containing 0.7 at.% carbon and 0.5 at.% boron have been obtained at room and elevated temperatures in air as a function of strain rate and compared to the response of a similar alloy without boron (i.e Fe–40Al–0.6C). Furthermore, tests were also conducted as a function of strain rate in oxygen at room temperature to elucidate the effect of environment on these properties. Both alloys contain a dispersion of a perovskite carbide within the grains and at grain boundaries. In addition, the quaternary alloy contains a fine dispersion of metastable borides and complex faults within the grains. Yield stress and tensile elongation appear strain rate insensitive (in the regime tested) for the boron-containing alloy at room temperature in oxygen, whereas some loss in elongation is encountered at the slowest rate in the ternary alloy; in all cases, fracture path is intergranular. In air, at room temperature, a strong strain-rate dependence of elongation is recognized in both alloys, their response being identical at the faster rates but diverging at the slow rates. A strong correlation is noted between the increase in percent transgranular cleavage and the drop in tensile elongation. The brittle-to-ductile transition temperature is sensitive to strain rate, shifting to higher temperatures rapidly with increasing strain rate. A variety of fracture paths is encountered depending on test temperature and strain rate.     

Application of experimental design to study and control properties and behaviour of cast Al–10 ? 8Si eutectic alloy

Abstract

An attempt was made to investigate the effect of compositional variationson the mechanical properties of an experimental T6 aged Al–10·8Si eutectic alloy. Experimental data were used to evaluate the regression coefficients of polynomial equations. The equations show that increasing Cu, Mn and Mg contents results in an increase in hardness and tensile strength. Copper makes the highest contribution of all three elements to the strength for the composition range studied. All four elements reduce the elongation and toughness, with Cu having the greatest effect. Detailed analysis indicates that the interaction coefficients of these variables do not appear to contribute significantly to the mechanical properties of the alloys. The accuracy of the equations in predicting the properties has been verified by carrying out random experiments in the range of variation of these four variables.     

The high-speed deformation behavior of TRIP steels

The high-speed deformation behavior of TRIP steel was investigated at strain rates ranging from 10⁻² s⁻¹ to 10³ s⁻¹. The effects of metallurgical factors, such as the rolling direction, thickness, and gage length, on the tensile properties at various strain rates were evaluated. The ultimate tensile strength, uniform elongation, strain rate sensitivity, absorbed energy, and strain-hardening exponent are reported. In general, the strength increases and the ductility decreases as the strain rate increases. The samples with a high amount of retained austenite had two distinct regions of strain rate sensitivity, showing high strain rate sensitivity over a strain rate of 10² s⁻¹. The tensile properties were not affected by the gage length and thickness of the tensile samples; however, the rolling direction of the tensile samples affected the UTS values slightly. The absorbed energy of the TRIP steel greatly exceeded that of HSLA steel.     

合金化对超薄铝合金翅片高温力学性能和组织的影响

采用高温拉伸试验、金相显微镜、扫描电镜等方法研究了Si、Zr、Fe合金化对超薄铝合金翅片高温性能和组织的影响。结果表明,3003和改性3003铝合金(3003mod)的强度均随着拉伸温度的升高而降低,而伸长率均先增大而后降低。3003mod铝合金在500℃时屈服强度较3003合金提高了32.2%。合金化显著提高了3003mod铝合金中纳米颗粒数量,降低了粗大微米相数量,其组织特征抑制了高温拉伸过程中的二次再结晶形核,较3003合金晶粒更粗、长宽比更大。二次再结晶是导致500℃下两种合金的伸长率较300℃下的急剧减小的根本原因。     

不同Zn/Cu质量比对Mg-Zn-Cu显微组织和性能的影响

论文采用光学显微镜、X射线衍射仪、扫描电子显微镜及显微硬度测试、室温和高温拉伸性能测试、蠕变性能测试研究了Ce和不同的Zn /Cu质量比对Mg-Zn-Cu显微组织和室温及高温力学性能的变化规律、高温变形性能、强化机制和抗蠕变性能的影响。研究结果表明,室温下挤压态Mg-8Zn-8Cu-Ce的拉伸强度和屈服强度分别为320 MPa和291 MPa,在423K温度下,拉伸强度仍高于220MPa。合金具有优良的蠕变性能,稳态蠕变速率为1.21×10_-8 s_-1,蠕变量仅为0.562%。在相同的变形温度下,铸造Mg-7Zn-3Cu-Ce的真实应力随着应变速率的增大而增大,表明合金是应变速率敏感材料。相同的应变速率下,合金的真实应力随着温度的升高而减小,但没有明显的动态再结晶和软化现象。     

真空感应重熔NiTi形状记忆合金室温拉伸力学性能

采用真空感应熔炼炉制备NiTi合金,并对重熔后的合金进行不同制度热处理。研究NiTi形状记忆合金边角料重熔合金不同温度时效后的室温拉伸力学性能。结果表明,NiTi形状记忆合金边角料重熔后,其室温屈服强度和抗拉强度均有不同程度的提高,断后延伸率略有增加,应力诱发马氏体相变对应的形状回复率降低;合金塑性变形能力随时效温度的升高而变差;合金中R相重新取向所提供的延伸率从总体上看比由单质原材料一次熔炼而成的合金要高。     

Influence of Applied Pressure on Tensile Behaviour and Microstructure of Squeeze Cast Mg Alloy AM50 with Ca Addition

The development of alternative manufacturing processes is essential for the success in applying Ca-containing magnesium alloys for automotive applications due to their relatively poor die castability. Squeeze casting with its inherent advantages has been demonstrated capable of minimizing the formation of casting defects in Mg-Al-Ca alloys. In this study, the effect of applied pressures on tensile behavior and microstructure of squeeze cast Mg-5wt.%Al-1%wt.%Ca alloy (AMX501) was investigated with the applied pressure varying from 3 to 90 MPa. The results of tensile testing indicate that the tensile properties of AMX501 alloy including ultimate tensile strength, yield strength, and elongation (E _f) increase from 153.7, 80 MPa and 3.26% to 183.7, 90.5, and 5.42% with increasing applied pressure levels from 3 to 90 MPa, respectively. The analysis of true stress versus strain curves shows that an increase in applied pressure levels result in high straining hardening rates during the plastic deformation of the alloy. Microstructural analysis and density measurements indicate that, as the applied pressure increases, the porosity levels of the alloy decrease considerably, despite of almost no significant reduction in grain sizes of the squeeze cast alloys due to their high aspect ratio of cylindrical castings. Hence, the improvement in tensile properties should be primarily attributed to casting densification resulting from applied pressures. The scanning electron microscopy observation on fractured surfaces reveals that the fracture modes of the squeeze cast alloys transit to ductile from brittle with increasing applied pressures.     

Microstructural characterisation and mechanical properties of Mg–xSn–5Al–1Zn alloys

Abstract

In this study, the microstructure and mechanical properties of as cast Mg–x Sn–5Al–1Zn alloys were investigated. The microstructures of the alloys were characterised by the presence of Mg₂Sn and Mg₁₇Al₁₂ precipitates. The greatest tensile strength and elongation were obtained at the alloy containing 5 wt-%Sn at room temperature. Microhardness of the alloys and volume fraction of the Mg₂Sn precipitates increased with increasing Sn content. Fractographic analysis demonstrated that dimple and cleavage facet were dominant mechanisms of these alloys tested at room and elevated temperature. The portion of cleavage facet was increased with the increment of Sn at the room and elevated temperatures.     

Dynamic tensile behaviors of AZ31B magnesium alloy processed by twin-roll casting and sequential hot rolling

The dynamic tensile behavior of twin-roll cast-rolled and hot-rolled AZ31B magnesium alloy was characterized over strain rates ranging from 0.001 to 375 s⁻¹ at room temperature using an elaborate dynamic tensile testing method, and the relationship between its mechanical properties and microstructures. It is observed that the sheet has a strong initial basal fiber texture and mechanical twinning becomes prevalent to accommodate the high-rate deformation. The yield strength and ultimate tensile strength monotonically increase with increasing the strain rate, while the strain hardening exponent proportionally decreases with increasing the strain rate due to twinning-induced softening. The total elongation at fracture distinctly decreases as the strain rate increases under quasi-static tension, while the effect of strain rate on the total elongation is not distinct under dynamic tension. Fractographic analysis using a scanning electron microscope reveals that the fracture is a mixed mode of ductile and brittle fracture.     

Mechanical properties of friction stir welded Al alloys with different hardening mechanisms

The mechanical properties of precipitation hardened Al 6061-T651 and Al 7075-T6 and strain hardened Al 5083-H32, friction stir welded with various welding parameters, were examined in the present study. 4 mm thick Al 6061-T651, Al 7075-T6, and Al 5083-H32 alloy plates were used for friction stir welding (FSW) with rotating speed varied from 1000 to 2500 rpm (rotation per minute) and welding speed ranging from 0.1 to 0.4 mpm (m/min). Each alloy displayed slightly different trends with respect to the effect of different welding parameters on the tensile properties of the FSWed Al alloys. The tensile elongation of FSWed Al 6061-T651 and Al 7075-T6 tended to increase greatly, while the tensile strength decreased marginally, with increasing welding speed and/or decreasing rotating speed. The tensile strength and the tensile elongation of Al 6061-T651 decreased from 135 to 154 MPa and 10.6 to 17.0%, respectively, with increasing welding speed from 0.1 to 0.4 mpm at a rotating speed of 1,600 rpm. Unlike the age-hardened Al 6061-T651 and Al 7075-T6, the strain-hardened Al 5083-H32 showed no notable change in tensile property with varying welding parameters. The change in the strength level with different welding parameters for each alloy was not as significant as the variation in tensile elongation. It was believed that the tensile elongation of FSWed Al alloys with varying welding parameters was mainly determined by the coarse particle clustering. With respect to the change in tensile strength during friction stir welding, it is hypothesized that two competing mechanisms, recovery by friction and heat and strain hardening by plastic flow in the weld zone offset the effects of different welding parameters on the tensile strength level of FSWed Al alloys.