The influence of alloy composition on microstructure and tensile behaviour of copper-lead alloys

Lead is a soft metal that possesses excellent antifriction and lubricating characteristics and is a desired addition to alloys which find use in friction-critical and low-load-bearing applications. The influence of alloy composition on microstructure, tensile properties and quasi-static fracture behaviour has been studied. Alloy composition, that is, lead content, was observed to have an influence on the size and distribution of lead globules in the copper matrix. The yield strength, ultimate tensile strength and elastic modulus of the alloy decreased with increase in lead content. The ductility of the alloys showed an improvement with increase in lead content. The influence of lead content on quasi-static fracture is discussed in detail.     

Mechanical properties of In-based eutectic alloy solders used in Josephson packaging

InBiSn and InSn eutectic alloy solders are used in the packaging of the cryogenic Josephson processor. The ductile behaviour of these alloys is important to the application of joints which experience large thermal stresses. In order to characterize the mechanical behaviour at cryogenic temperatures, tensile and shear strengths of bulk solders were measured at and below room temperature. It is found that the ultimate tensile and shear strengths of bulk solders increase as temperature decreases. At low temperatures, the ultimate tensile strength of InBiSn alloy is about three times less than that of InSn alloy. The ductility of both alloys reduces at low temperatures. The fracture surfaces of both bulk solders and solder joints having an interface material (Pd and Au thin films) to the electrical contact pads (Nb thin film) were examined using SEM. Ductile fracture mode was observed for all the specimens down to liquid nitrogen temperature.     

The influence of manganese addition on mechanical properties of commercial Al‐4Mg casting alloys

The aim of this study was to investigate the mechanical properties of Al‐Mg‐Si alloys aged to peak hardness with different dispersoid volume fraction. It was found that the tensile strength increases with dispersoid content, for alloys having similar ductility. The effect of an increasingly triaxial stress state on a fracture strain above mentioned alloys were measured using a series of notched tensile specimens whose notch root radius of curvature was changed. The alloy ductility was found to increase with dispersoid content and root radius and to decrease with increased stress triaxiality. The fracture toughness of these alloys was determined as a function of dispersoid content and notch root radius of curvature. It was observed that the fracture toughness increased as the dispersoid content and the notch root radius increased. scanning electron microscope analysis of the fracture surfaces revealed that fracture mechanism was transgranular fracture with dimples formation. It is argued that optimum mechanical properties in these alloys can be achieved at about 0.5 % Mn content.     

Microstructure,tensile properties and fracture behaviour of an Al-Cu-Li-Mg-Zr alloy 8090

The addition of lithium to aluminium alloys has the potential for providing a class of high strength alloys with exceptional properties suitable for aerospace applications. One such candidate is 8090, a precipitation hardenable Al-Li-Cu-Mg alloy. Detailed optical microscopical observations were used to analyse the intrinsic microstructural features of the alloy. It is shown that microstructural characteristics have a pronounced influence on tensile properties and fracture behaviour of the alloy in the peak-aged, maximum strength condition. Tensile test results indicate that the alloy has property combinations comparable with other high strength commercial aluminium alloys. The elongation and reduction in area are higher in the transverse direction of the extruded plate. A change in fracture mode was observed with direction of testing. We rationalize such behaviour based on the grain structure of the material, and the nature, distribution and morphology of the second-phase particles. An attempt is made to discuss the kinetics of the fracture process in terms of several competing mechanistic effects involving intrinsic microstructural features, deformation characteristics of the matrix, brittleness of the grain boundary precipitates and grain boundary failure. The role of stress on particle fracture is highlighted.     

Influence of deformation processing on tensile response of dispersion strengthened copper

Abstract

The influence of deformation processing on microstructure, tensile deformation, and fracture behaviour of an oxide dispersion strengthened copper alloy is presented and discussed. The strength of the alloy, in both the drawn and extruded microstructural conditions, decreased with an increase in test temperature. At a given temperature, the strength of the drawn microstructure was superior to that of the extruded counterpart. For both the drawn and extruded microstructures, the alloy maintained a high value of yield strengthultimate tensile strength ratio. The tensile fracture behaviour of the alloy was identical for both the drawn and extruded microstructures. Tensile deformation was essentially by inhomogeneous planar slip in the copper matrix and at locations remote from the dispersoid particles.     

Al-Zn-Mg-Cu系超高强度铝合金的研究现状与发展趋势

分析了近年来超高强度Al-Zn-Mg-Cu系铝合金的成分设计、工艺优化、显微组织分析、力学性能测试及微量元素的作用，对今后的发展动向提出了一些新的看法：采用传统铸造技术得到的铝合金，Zn含量的最大值在8wt％左右，抗拉强度低于700MPa；采用喷射成形技术，Zn含量最大值能够超过12wt％，同时抗拉强度可达800MPa以上，大大提高了铝合金的强度；超高强度铝合金的固溶强化相主要为MgZn2相；经回归时效处理(RRA)后，合金同时具有T6的强度和T7X的抗应力腐蚀性能；微量元素对超高强度铝合金的组织和性能具有显著的影响。     

Effect of Si content on microstructure and mechanical properties of Al–Si–Mg alloys

Microstructure and mechanical properties of as-cast and as-extruded Al–Si–Mg alloys with different Si content are investigated by tensile test, microstructure observation. High density of Si particles in the Al alloys can induce dynamic recrystallization during hot extrusion and it becomes more matured with an increase in the density of Si particles. The tensile strength of as-cast and as-extruded alloys can be improved with the increase of Si content and hot extrusion make the elongation of alloys increase dramatically. Considerable grain refining effect caused by recrystallization occurred during hot extrusion of S2 (equivalently commercial A356 alloy) and S3 (near eutectic alloy) alloys plays an important role in the improvement of elongation. A good combination of strength and elongation for the as-extruded S3 alloy indicates that near eutectic Al–Si alloys can be hot-extruded to produce aluminum profiles with high performance.     

Morphology and mechanical properties of melt-spun and conventionally cast aluminium,AlMg and AlSi alloys before and after hot extrusion

Rapidly solidified aluminium, AlMg (0 to 16.5 at % Mg) and AlSi (0 to 20.2 at % Si) alloys were produced by melt spinning. The AlMg ribbons were single-phase, whereas the AlSi ribbons were dual-phase. In the ribbons of both alloy systems the fineness of the microstructure increased with increasing alloying element content. The melt-spun ribbons were consolidated by hot extrusion. For comparison, conventionally cast alloys of corresponding compositions were extruded analogously. During the extrusion process in AlMg (16.5 at % Mg) and in the AlSi alloys precipitation occurred. The consolidation of the ribbons was markedly influenced by the oxide layer on the ribbon surfaces: in the AlSi consolidates a more intimate contact between the ribbons was apparent than in the aluminium and AlMg consolidates. In the extrudates of the conventionally cast alloys the grains and second-phase particles were much larger than in the consolidates. The observed dependence on alloy composition of hardness, ultimate tensile strength and elongation at fracture of both consolidated ribbons and extrudates of the conventionally cast alloys are discussed in terms of matrix grain size, solute content of the matrix, amount and size of second-phase particles and recrystallization behaviour. For all compositions of the alloys the Vickers hardness of the as-melt-spun ribbons was higher than that of the consolidated products, owing to recrystallization and precipitation provoked by the hot consolidation process. The ultimate tensile strength as well as the elongation at fracture of both consolidated ribbons and extruded conventionally cast alloys did not differ significantly for AlMg. However, due to a finer microstructure and a stronger inter-ribbon bonding, for AlSi alloys with a high silicon content the rapid solidification processing route did yield a product with significantly improved mechanical properties as compared with the extruded conventionally cast alloys.     

Ageing and toughness of silicon carbide particulate reinforced Al-Cu and Al-Cu-Mg based metal-matrix composites

Metal-matrix composites (MMC) comprising powder aluminium alloys reinforced by particulate ceramic are being developed for widespread aerospace structural applications ranging from fuselage and missile components to undercarriage parts. Most interest is centred on MMCs with an Al-Cu-Mg (2124) matrix alloy. These MMCs possess high levels of specific stiffness with high specific strengths but can exhibit lower ductility and toughness than conventional unreinforced aluminium alloys.To overcome these problems the effects of alloy composition on the ageing behaviour and notched tensile properties of Al-Cu-Mg and Al-Cu based alloys reinforced with 20 wt% silicon carbide particulate have been investigated.Al-Cu-Mg MMCs gave higher strengths and moduli than unreinforced sheet. Lowering the copper and magnesium content resulted in reduced strength but did not affect the rate of age hardening. The Al-Cu-MMCs gave the lowest strengths but the absence of natural ageing may prove advantageous, enabling sheet to be formed and subsequently heat-treted to the peak strength condition.     

Effects of zinc coating on magnesium alloy–steel joints produced by cold metal transfer method

Magnesium alloys are lap-joined to galvanised and bare steel sheets by a cold metal transfer method. The weld appearance, cross-section, tensile strength and fracture behaviour of these joints are characterised by scanning electron microscopy, tensile tests and energy-dispersive spectroscopy. The joints were found to have good weld appearance and satisfactory tensile strength. The spreadability and wettability of the Mg alloy–galvanised steel joint are superior to those of the Mg alloy–bare steel joint, but the tensile strength is lower. In particular, the presence of Zn on the galvanised steel sheet improves wettability but decreases tensile strength. Aluminium has a high affinity for Fe, and the thinner layer of Fe–Al improves the mechanical properties of the Mg alloy–bare steel joint.     

Ti-10Mo-XNb合金铸态组织和机械性能的研究

为了研究Nb元素对Ti-10Mo合金组织和性能的影响,采用钨电极熔化、离心浇注工艺制备了4种钛合金(Ti-10Mo-XNb,X=0,3,7,10),分析并测试了Nb元素对Ti-10Mo合金铸态组织和力学性能的影响.研究结果表明:随着Nb含量的增加,3种Ti-Mo-Nb合金的铸态组织和相组成发生了改变,Ti-10Mo-3Nb合金由等轴的α+β晶粒组成,Ti-10Mo-7Nb合金由等轴的β晶粒组成,Ti-10Mo-10Nb合金由少量等轴和大量枝状的β晶粒组成.另外,随着Nb含量的增加,3种Ti-Mo-Nb合金的维氏硬度、压缩强度、弹性模量降低,压缩率和抗弯强度升高,压缩断口和弯曲断口由脆性断裂向韧性断裂转变.Ti-Mo-Nb合金有望成为新型的生物医用材料.     

热处理对AZ31B镁合金轧板组织和性能的影响

研究了AZ31B镁合金轧板经不同温度、时间退火后的组织和性能及其再结晶行为。结果表明,热轧板材在退火过程中主要发生再结晶;退火后,强度略有下降,但伸长率明显提高;在523K下退火,保温60min,可获得平均晶粒直径为10μm的细晶组织,其抗拉强度为258MPa,断裂伸长率为22.3%,综合性能较好。热轧态板材呈脆性准解理断裂,退火后转变为韧性断裂。     

Structural modification of Al-Si eutectic alloy by Sr and its effect on tensile and fracture characteristics

Modification of the commercial A-S13 alloy and high purity Al-Si eutectic alloy has been successfully achieved using Al-5 Sr master alloy. The refined structure showed more fine and uniformly distributed eutectic silicon in the high purity alloy. The incidence of Al-dendrites due to modification was related to the movement of the eutectic point to the higher-silicon side. The chill-cast alloys showed better refined structure and higher mechanical properties in comparison with the sand-cast alloys. The modified chill-cast alloy exhibited the best mechanical properties. The ultimate. tensile strength of which reached 280 M Pa and the elongation was 9.2%. The fracture patterns changed from well faceted brittle appearance to smooth silky and dimple-like for the normal and modified alloys respectively. This reflects the change from brittle to ductile behaviour after modification. A model for the fracture mechanism was proposed to explain the observed higher ductility for the modified alloy.     

Correlation between ultimate tensile strength and solidification microstructure for the sand cast A357 aluminium alloy

Many studies have demonstrated a relationship between secondary dendrite arm spacing (SDAS) and the mechanical behaviour of cast aluminium–silicon alloys, both for tensile and fatigue strength. SDAS is related to the solidification time and can be predicted, with a good approximation, by finite-element simulation. However, other microstructural features can affect the tensile behaviour of cast aluminium alloys such as size and morphology of the eutectic Si particles, grain size, composition and morphology of the intermetallic compounds. The present investigation was aimed at finding valuable relationships between ultimate tensile strength and the previously mentioned microstructural parameters for the sand cast A357 aluminium alloy. The microstructural characterization was carried out by optical microscopy and image analysis on more than about 2500 micrographs. Starting from the microstructural parameters and taking into account the material hardness, a relationship able to predict the ultimate tensile strength of the alloy, with an error less than 5%, was found. This relationship can be used to evaluate the local values of the UTS in complex cast components knowing only the hardness and the microstructural parameters, even in positions where the extraction of tensile specimens is not possible.     

Bi-Pb-Sn-Cd易熔合金的设计与性能研究

根据铋基合金的特点与合金相图,设计了不同成分的Bi Pb Sn Cd易熔合金;并利用差热分析仪、X射线衍射仪及力学检测设备等研究了成分对合金熔点、组织和抗拉强度的影响。结果表明,设计的易熔合金由Bi、Pb7Bi3、Sn和Cd等物相组成;合金的熔点均在72℃左右。随Cd、Bi元素含量的增加,液相线温度逐渐降低;Cd元素对合金熔程、抗拉强度的影响最大,Sn元素次之,Pb元素的影响最小。正交试验表明,Bi 30Pb 15Sn 9Cd合金的综合性能最佳。     

Tensile and fracture behaviour of PP/wood flour composites

Polypropylene/wood flour composites with different fibre content were prepared. The effect of composition and the incorporation of maleinated polypropylene on the materials tensile and fracture and failure behaviour was investigated. Reliable fracture toughness data that will be useful for structural applications were obtained. In unmodified composites an increase in Young´s modulus was found with the addition of wood flour to PP, whereas tensile strength, strain at break and fracture toughness were observed to decrease as fibre content increased. The presence of MAPP was beneficial to tensile strength and ductility and had no significant effect on fracture toughness, as a result of enhanced fibre dispersion within the matrix and improved interfacial adhesion. Although reduced ductility and toughness were observed for the composites respect to the matrix, in the case of modified composites, environmentally friendly stiffer materials were obtained with cost saving without sacrificing strength.     

The effect of anodising on the fatigue performance of self-tapping aluminium screws

Self-tapping aluminium screws are an innovative joining technology for the assembly of lightweight components in industrial scale. It has been established in the past that porous anodic oxide coatings in many cases reduce the fatigue strength of specimens without notches. In the present work, the fatigue behaviour of notched specimens, i.e. self-tapping screws made from aluminium alloys EN AW-6056, 6082 (both in a conventional state and in a fine-grained state produced by equal channel angular pressing – ECAP) and 7068 with and without oxide coatings is examined. The coatings are produced by hard anodising and are necessary for the thread-forming process during assembly. While the coatings do not affect the static tensile strength, they reduce the fatigue strength for the specimens of the 6056 and the 6082 alloy. For the 7068 alloy a slight increase in fatigue strength is discovered on a low load horizon. The scatter of endured fatigue cycles until fracture of specimens is generally reduced by the anodic oxide coatings.     

Influence of Stress‐Aging Processing on Precipitates and Mechanical Properties of a 7075 Aluminum Alloy

Two‐step stress‐aging tests, as well as pre‐treatment plus stress‐aging experiments, are performed on a 7075 aluminum (Al–Zn–Mg–Cu) alloy. Influences of stress‐aging parameters on mechanical behavior and fracture mechanism are investigated through uniaxial tensile test and fracture morphology analysis. It is revealed that the stress‐aging dramatically influences the mechanical properties and fracture characteristics of the studied alloy, which is contributed to the sensitivity of microstructures to stress‐aging. When the alloy undergoes two‐step stress‐aging, the ultimate tensile strength and yield strength first increase and then decrease with the increased first step stress‐aging temperature, while the elongation first decreases and then increases. For the retrogression pre‐treated plus stress‐aged alloy, the yield strength first increases and then drops with the increased retrogression pre‐treatment time, while the ultimate tensile strength almost remains stable. Furthermore, the elongation continuously increases with the increased retrogression pre‐treatment time. The observation of fracture morphology indicates that the dimple‐type intergranular fracture is the main fracture mechanism for the two‐step stress‐aged and retrogression pre‐treated plus stress‐aged alloys.     

Grain size effects on the mechanical properties of some squeeze cast light alloys

Mechanical property-grain size relationships have been examined for squeeze cast Al-4.5% Cu alloy, for an aluminium alloy with a composition corresponding to wrought 7010, and for a magnesium alloy AZ91. The general trend of the results obtained showed that the tensile properties and the fatigue strength improved as grain size decreased and the reverse was found to be the case for the fatigue crack propagation resistance and fracture energy of these castings. However, the results also showed that no simple common relationship existed between grain size and the tensile properties of the different alloys. The results are discussed in respect of their microstructures.     

Ta含量对高性能镍基粉末高温合金高温拉伸性能的影响

使用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)和高温拉伸试验机等手段系统地研究了不同Ta含量FGH98合金的显微组织和高温拉伸性能。结果表明：添加Ta可明显消除原始粉末颗粒的边界(PPB,Prior Particle Boundary),促进二次γ′相形态失稳和三次γ′相数量的增加。加入Ta使合金的高温抗拉强度和屈服强度都有一定程度的提高,Ta含量为2.4%(质量分数,下同)的合金塑性最好;无Ta和1.2%Ta合金的拉伸断口为结晶状断口;2.4%Ta合金的断口上有较多的等轴状韧窝,为韧性断裂;3.6%Ta和4.8%Ta合金为穿晶和沿晶解理断裂,属于典型的结晶状断口。在无Ta合金中产生大量孪晶和位错绕过γ′相发生变形,Ta的加入降低了合金的层错能,随着Ta含量的提高合金的位错剪切γ′相产生大量的层错。