Developing aluminium–zinc-based a new alloy for tribological applications

In order to develop aluminium–zinc-based a new alloy for tribological applications, six binary Al–Zn and seven ternary Al–25Zn–(1–5)Cu were prepared by permanent mould casting. Their microstructure and mechanical properties were investigated. Dry sliding friction and wear properties of the ternary alloys were investigated using a pin-on-disc machine. Surface and subsurface regions of the wear samples were studied with scanning electron microscopy (SEM). The highest hardness and tensile strength were obtained with the Al–25Zn alloy among the binary ones. The microstructure of this alloy consisted of aluminium-rich α and eutectoid α + η phases. Addition of copper to this alloy resulted in the formation of θ (CuAl₂) phase. The hardness of the ternary alloys increased with increasing copper content. The highest tensile and compressive strengths and wear resistance and the lowest friction coefficient were obtained from the ternary Al–25Zn–3Cu alloy. The dimensional change measured on ageing (stabilization) of this alloy was found to be much lower than that obtained from the copper containing zinc-based alloys. Microstructural changes were observed below the surface of the wear samples of the Al–25Zn–3Cu alloy. These changes were related to the heavy deformation of the surface material due to normal and frictional forces, and smearing and oxidation of wear material. Adhesion was found to be the main wear mechanism for the alloys tested.     

Influence of T5 heat treatment on the microstructure and lubricated wear behavior of ternary ZnAl40Cu2 and quaternary ZnAl40Cu2Si2.5 alloys

A ternary ZnAl40Cu2 and a quaternary ZnAl40Cu2Si2.5 alloys were produced by permanent mold casting and subjected to T5 heat treatment at a temperature of 150 °C for 24 hours. The structural, mechanical and lubricated wear properties of these alloys were investigated in the as-cast and heat-treated conditions and the results were compared with those of SAE 65 (CuSn12) plain bearing bronze. Microstructure of the ternary alloy consisted of aluminum-rich α, eutectoid conversion product of α+η and ϵ phase located in the interdendritic channels. In addition to these phases, silicon particles were observed in the microstructure of the quaternary alloy. T5 heat treatment caused a considerable amount of reduction in the hardness, tensile strength and wear resistance of ZnAl40-based ternary and quaternary alloys, but improved their ductility and stability. These alloys in the as-cast and heat-treated conditions exhibited lower wear volume or higher wear resistance than SAE 65 bearing bronze. Among the experimental alloys, the optimum mechanical properties and wear performance were obtained from ZnAl40Cu2Si2.5 alloy in both as-cast and heat-treated conditions. Adhesion appeared to be the main wear mechanism for the ZnAl40-based alloys, but abrasion dominated the wear of SAE 65 bronze.     

The effect of composition segregation on the friction and wear properties of ZA48 alloy in dry sliding condition

In this study, the effect of composition segregation on the wear resistance of high aluminum zinc-based alloy is investigated. The test results show that the improving wear resistance is due to a combined action of α and η phase. The rich solid solution of α−Al has higher strength and load bearing capability than of η phase. Under the action of the sliding friction, the hard α phase was protruded from matrix and acted as a loading phase. The η phase helped to act as a type of natural lubricant in sliding wear situations. Meanwhile, the iron transferred from the steel ring to block and forced to the recess continuously, which forms a thin protective film at the contact surface, then the load bearing capability of the test alloy would be improved.     

Effect of strain rate and environment on the mechanical properties of the Ni–19Si–3Nb–0.15B–0.1C intermetallic alloy at high temperatures

The effect of strain rate and environment on the mechanical behavior at different temperatures of the Ni–19Si–3Nb–0.15B–0.1C alloy is investigated by atmosphere-controlled tensile testing under various conditions at different strain rates and different temperatures). The results reveal that the Ni–19Si–3Nb–0.15B–0.1C alloy exhibits ductile mechanical behavior (UTS ∼ 1250 MPa, ε ~ 14%) at temperatures below 873 K under different atmosphere conditions. However, the alloy without boron and carbon addition shows ductile mechanical behavior only when the sample is tested in vacuum. This indicates that the microalloying of boron and carbon does overcome the environmental embrittlement from water vapor at test temperatures below 873 K for the Ni–19Si–3Nb base alloy. However, the boron and carbon doped alloy still suffers from embrittlement associated with oxygen at a medium high temperature (i.e. 973 K). In parallel, both of the ultimate tensile strength and elongation exhibit quite insensitive response with respect to the loading strain rate when tests are held at temperatures below 873 K. However, the ultimate tensile strength exhibits high dependence on the strain rate in air at temperatures above 873 K, decreasing the ultimate tensile strength with decreasing strain rate.     

Effects of Zr and B on the structure and tensile properties of Al–20%Mg alloy

In current research, the effects of different Zr and B contents on the structure and tensile properties of Al–20%Mg alloy have been investigated by using Al–15Zr and Al–8B master alloys. Optical and scanning electron microscopy (SEM) were utilized to study the microstructures and fracture surfaces. Microstructural analysis of the cast alloy showed dendrites of primary α-phase within the eutectic matrix which consists of β-Al₃Mg₂ intermetallic and α-solid solution. After tensile testing, the optimum amounts for both Zr and B were found to be 0.5 wt.%. Ultimate tensile strength (UTS) value of the unrefined alloy increased from 168 MPa to 243 MPa and 236 MPa by adding 0.5% Zr and 0.5%B, respectively. The main mechanism for UTS enhancement was found to be due to the refinement of grains and also altering large dendrites of Al(α)-phase to finer structure. The study of fracture faces revealed that B/Zr addition changes the mode of fracture from brittle to rather ductile.     

Tensile strength improvement of an Mg–12Gd–3Y (wt%) alloy processed by hot extrusion and free forging

An Mg–12Gd–3Y (wt%) alloy was prepared by conventional casting method using permanent steel mold. Then this alloy was subjected to hot processing, involving hot extrusion and free forging. Tensile strength at room temperature can be improved, with the highest ultimate tensile strength (UTS) value of 390.2 MPa achieved by hot extrusion in comparison to that of as-cast alloy. Temperature dependence of tensile strength is distinguishable for the as-extruded alloy, while the relative stability in UTS values of the alloy after being freely forged should be ascribed to the inter-crossing among deformation bands located at various orientations and the accommodation effect of twining lamellas resulting from forging process on plastic deformation during tensile test at elevated temperatures. Further annealing after hot processing can only have adequate influence on the tensile strength of as-forged alloy. For the alloy freely forged and annealed at 523 K for 4 h, the highest UTS (441.1 MPa) at room temperature is found, which should be mainly related to an evolution from the original as-forged microstructure with subgrains to a more stable combination of large and refined grains through dynamic recrystallization during free forging, and the stress at offset yield YS (384.3 MPa) is also comparable to that relatively high value of 396.9 MPa after solution treatment and isothermal aging of the as-cast alloy.     

Mechanical properties of the Ni3(Si,Ti) alloys doped with carbon and beryllium

The Ni₃(Si, Ti) alloys doped with small amounts of carbon and beryllium were tensile tested in two environments, vacuum and air, over a wide range of test temperatures. The yield stresses of the carbon-doped alloys were almost identical to the undoped alloys while those of the beryllium-doped alloys were slightly higher than the undoped Ni₃(Si, Ti) alloys. The doping with carbon enhanced the elongation and ultimate tensile strength (UTS) whereas doping with beryllium reduced the elongation over the entire temperature range tested. The fracture patterns were primarily associated with the ductility behaviour. As the elongation (or UTS) increased, the fracture pattern changed from the intergranular to the transgranular fracture patterns. No environmental embrittlement of the ductility of the carbon-doped alloys was found at ambient temperatures but it was evident at elevated temperatures. Ductilities were reduced at high temperatures when the carbon-doped alloys were tensile tested in air. At high temperatures the environmental embrittlement observed is suggested to be due to the penetration of (free) oxygen into the grain boundaries causing the ductility loss in the carbondoped alloys.     

Investigation of the abrasive wear behaviour of ZA-27 alloy and CuSn10 bronze

In this study, abrasive wear behaviours of ZA-27 alloy and CuSn10 bronze were investigated using a purpose-built wear tester. The ZA-27 alloy was produced by permanent mould casting. The abrasive SiC particles having 63 μm grit size was added to the lubricant oil. The wear rate and friction coefficient of alloys were determined at the different test conditions such as sliding distance, applied load, linear velocity and percentage SiC weight content. The wear surfaces of alloys were examined using SEM and EDS analysis. The results showed that the wear rate of alloys decreased with the increasing of applied load and increased with the increasing linear velocity and abrasive SiC content. It was found that the SiC particle fracture was an important mechanism determining the friction and the wear rate of alloys. CuSn10 bronze showed higher wear resistance than ZA-27 alloy under abrasive test conditions except at high linear velocities.     

The effect of metastability on room temperature deformation behavior of β and α + β titanium alloys

The deformation behavior of single-phase metastable β-titanium alloys and two-phase α+metastable-β alloys strongly depends on the degree of stability of the β-phase. Recently, it has been shown that the tensile deformation behavior, as well as the creep deformation behavior at low temperatures (<0.25T _m), is strongly influenced by the degree of metastability. For example, the titanium β-alloy Ti–13.0wt%Mn, which has higher stability than the titanium β-alloy Ti–14.8wt%V, deforms by slip only; whereas the latter deforms by slip and twinning. In addition to the mechanical properties, the deformation mechanisms also depend on the degree of metastability. Further, the deformation mechanisms of a given metastable β-alloy depend on whether the β-phase is present by itself as a single-phase alloy, or in the presence of α-phase in the form of a two-phase alloy. For example, it was found that a metastable Ti–V alloy deforms by slip and twinning when it is in the form of a single-phase alloy, but deforms by slip and martensitic transformation when the same metastable β-phase is present in a two-phase α + β alloy. The mechanical properties of the metastable β alloys in turn depend on these deformation mechanisms. These recent developments are reviewed in this article.     

Hot tensile properties and microstructural evolution of as cast NiTi and NiTiCu shape memory alloys

Hot tensile properties of as cast NiTi and NiTiCu shape memory alloys were investigated by hot tensile test at temperature range of 700–1100 °C using the strain rate of 0.1 s⁻¹. The NiTi alloy exhibited a maximum hot ductility at temperature range of 750–1000 °C, while the NiTiCu alloy showed it at temperature range of 800–1000 °C. It was found that at temperatures less than 750 °C, diffusion-assisted deformation mechanism was inactive leading to semi-brittle type of failure and limited ductility in both alloys. Also it was found that at temperature range of 800–1000 °C, dynamic recrystallization is dominant leading to high ductility. Likewise, the fracture surface of the specimens presenting the maximum hot ductility showed an ideal type of ductile rupture in which they gradually pulled out to a fine point. On the other hand, the decline in ductility occurred at the temperatures above 1000 °C was attributed to the liquid phase formation leading to interdendritic and intergranular type of fracture.     

Effects of alloying elements on mechanical and thermal characteristics of Al-6wt-%Si-0.4wt-%Mg–(Cu) foundry alloys

The objective of this study was to investigate the effects of alloying elements on mechanical and thermal characteristic of Al-6wt-%Si-0.4wt-%Mg–(Cu) foundry alloys after heat treatment using a universal testing machine and a laser flash apparatus. Solid solution treatment of samples was carried out at 535°C for 6?h before quenching samples in warm water. Artificial ageing treatment was conducted at various temperatures ranging from 180 to 220°C for 5?h. When Cu was added to increase the mechanical strength of Al-6wt-%Si-0.4wt-%Mg alloy, its thermal conductivity decreased. After adding 0.1wt-%Ti to an Al-6 wt-%Si-0.4wt-%Mg-0.9wt-%Cu alloy, ultimate tensile strength (UTS) was improved 18?MPa compared to that of Ti-free alloy at ageing temperature of 180°C. The addition of Ti facilitated the formation of θ′-Al₂Cu and Q′-phase, which resulted in increased UTS at room temperature. In the case of Cu-free Al-6wt-%Si-0.4wt-%Mg alloy, adding Ti to the alloy did not affect the UTS.     

The role of active elements in Fe-Cr-Al alloys for heating element applications

The role of active elements (zirconium, cerium and yttrium) in grain growth and its subsequent effect on room-temperature tensile fracture behaviour of Fe-Cr-Al alloys has been investigated. The alloys containing active elements exhibited improved resistance to grain growth. Yttrium-containing alloy retained higher room-temperature tensile ductility even after heating at higher temperatures because of its superior resistance to grain coarsening. All the alloys, with and without active elements, exhibited a sudden drop in room-temperature tensile ductility, with concommitant change in fracture mode from dimple rupture to cleavage, in a narrow band of 39–44μm grain size. The ductile-brittle transition temperatures (DBTT) of these alloys were found to be 150°C and 215°C for grain sizes 25μm and 100μm respectively. The accelerated life test showed that the alloys containing active elements exhibited longer lives.     

Investigation of microstructures and tensile properties of a Sn-Cu lead-free solder alloy

In recent years, the pollution of environment from lead (Pb) and Pb-containing compounds in microelectronic devices attracts more and more attentions in academia and industry, the lead-free solder alloys begin to replace the lead-based solders in packaging process of some devices and components. In this work, microstructures and mechanical properties of the lead-free solder alloy Sn99.3Cu0.7(Ni) are investigated. This paper will compare the mechanical properties of the lead-based with lead-free solder alloys (Sn99.3Cu0.7(Ni) and 63Sn37Pb). The tensile tests of lead-based and lead-free solder alloys (Sn99.3Cu0.7(Ni) and Sn63Pb37) were conducted at room and elevated temperature at constant strain rate; the relevant tensile properties of Sn99.3Cu0.7(Ni) and Sn63Pb37 were obtained. Specifically, the tensile strength of this lead-free solder- Sn99.3Cu0.7(Ni) in 25^∘C, 50^∘C, 75^∘C, 100^∘C, 125^∘C was investigated; and it was found that tensile strength of the lead-free solder decreased with the increasing test temperature at constant strain rate, showing strong temperature dependence. The lead-free solder alloy Sn99.3Cu0.7(Ni) was found to have favorable mechanical properties and it may be able to replace the lead-based solder alloy such as Sn63Pb37 in the packaging processes in microelectronic industry.     

Mechanical, physical, and chemical characterization of Ti–35Nb–5Zr and Ti–35Nb–10Zr casting alloys

Titanium is used due its excellent properties in medical and dentistry areas. With the objective of exploiting better mechanical properties, not altering its biocompatibility, it was intended to add niobium and zirconium to the titanium, being formulated two alloys Ti–35%Nb–5%Zr (alloy 1) and Ti–35%Nb–10%Zr (alloy 2) wt% produced by an arc melting method. The chemical analysis of the samples was accomplished by X-ray fluorescence, and the microstrutural evaluation by scanning electron microscopy and X-ray diffraction. The mechanical tests were: Vickers hardness, tensile strength, mechanical cycling, and fracture analysis. The results allowed characterizing the alloy 1 as α + β type and the alloy 2 as β type. It is found that the alloy 1 presented larger hardness and smaller tensile strength than the alloy 2. The fractures, after the tensile test, were of the ductile type and, after the mechanical cycling, they were of the mixed type for both alloys.     

Creep rupture of lead-free Sn-3.5Ag and Sn-3.5Ag-0.5Cu solders

The aim of this study is to investigate the creep rupture behavior of lead-free Sn-3.5Ag and Sn-3.5Ag-0.5Cu solders at three temperatures ranging from room temperature (RT) to 90 °C, under a tensile stress range of σ/E=10⁻⁴ to 10⁻³. The ultimate tensile strength (UTS) and creep resistance were found to be decreased with increasing temperature for each given lead-free solder. Both the binary and ternary Ag-containing alloys exhibited superior UTS and creep strength to the conventional Sn-37Pb solder at a similar temperature. Due to a more uniform distribution of eutectic phases and a larger volume fraction of intermetallic compounds (IMCs), the Sn-3.5Ag-0.5Cu alloy had greater UTS and creep strength than did the eutectic Sn-3.5Ag solder at each testing temperature. The stress exponents (n) of minimum strain rate (˙ε_min) were decreased from 7 and 9 at RT to 5 and 6 at 60 and 90 °C, for the binary and ternary lead-free alloys, respectively. Fractography analyses revealed typical rupture by the nucleation and growth of voids/microcracks at IMCs on the grain boundaries. Both Monkman-Grant and Larson-Miller relationships showed good results in estimating the rupture times under various combinations of applied stress and temperature. A model, using a term of applied stress normalized by Young’s modulus, was proposed to correlate the rupture times at various temperatures and could explain the rupture time data reasonably well for the given two lead-free solders.     

Effect of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y magnesium alloy

The influence of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y (wt.%) magnesium alloy was investigated. The grain size of alloys decreased with Zr content from 0% to 0.93% (wt.%). The addition of Zr greatly improved the ultimate tensile strength (UTS) and the elongation (EL), while slightly improved the tensile yield strength (TYS). The UTS and the EL of the alloy containing 0.93% Zr increased by 125.8 MPa and 6.96% compared with base alloy, respectively. The corrosion resistances were found to decrease with Zr content from 0% to 0.42% and then increase from 0.42% to 0.93%. The differences in the sizes and distributions of the Zr-rich particles have significant effects on the corrosion behaviors. The alloy with 0.42% Zr addition revealed the optimum combination of mechanical properties and corrosion resistance.     

Tensile properties of high-pressure die-cast AM60 and AZ91 magnesium alloys on microporosity variation

The effect of microporosity on the variability in the tensile properties of high-pressure die-cast AM60 and AZ91 alloys was investigated, together with a theoretical prediction based on a constitutive model. The strain rate sensitivity of both alloys was measured through an incremental strain rate change test at room temperature, and the microporosity was measured through quantitative fractography analyses on the fractured surface. The variability in the tensile strength and elongation of both alloys can be empirically described as a power law relationship in terms of the microporosity variation. The defect susceptibility of the UTS and elongation to the microporosity variation in the AZ91 alloy is slightly higher than that in the AM60 alloy. The constitutive prediction on the tensile properties of the AM60 and AZ91 alloys is in good agreement with the experimental results, and it suggests that the defect susceptibility of the tensile properties to the microporosity variation is significantly decreased with the increase of strain hardening exponent.     

Aging behavior of 359-type Al–9%Si–0.5%Mg casting alloys

The present study investigated the influences of aging temperature and time on the tensile properties and quality indices of 359-type Al–9%Si–0.5%Mg casting alloys. These alloys are still not widely used by most foundrymen in spite of the fact that they are extremely promising for several fields of engineering applications because of their superior strength. For the purposes of validating their use in industrial applications, a solid data base was created, based on the present study, correlating the tensile properties and the quality indices of these alloys with the aging parameters. Quality charts were used as an evaluation tool for selecting the optimum aging conditions for developing high strength and optimum quality in 359 casting alloy. Aging at a low temperature was observed to produce the greatest strength and optimum quality in the 359-type castings compared to aging at higher temperatures. The peak-strength for 359 alloy was observed to be attained after shorter aging times on condition that the aging temperature is increased. The aging times required for reaching peak-strength in 359 alloys are 32, 24, 1 h, 30, and 10 min when applying aging temperatures of 155, 170, 195, 220, and 245 °C, respectively. Aging treatment at higher temperatures is accompanied by a reduction in the tensile properties and quality index values of the castings; however, it also introduces the possibility of a significant economical strategy for minimizing the time and the cost of this treatment. Depending on the required level of tensile properties and based on the quality charts developed, it is possible to make a rigorous selection as to the most suitable aging parameters to be applied to the 359 alloy so as to obtain the best possible cost-effective compromise between alloy strength and quality.     

Mechanical behaviour of a new dispersion-strengthened bronze

The characteristics of a new dispersion-strengthened bronze developed by the Mixalloy system were evaluated through their mechanical properties and compared to commercial phosphorous bronze. Annealing treatment in the temperature range 400–750 °C did not produce any difference in the tensile properties of dispersion-strengthened bronze, but increasing the cold-drawing ratios resulted in a rapid increase in the tensile and yield strength. The tensile and yield strengths of cold-drawn dispersion-strengthened bronze after extrusion decreased with increasing annealing temperatures, but did not decrease greatly in the temperature range above 500 °C. The new dispersion-strengthened bronze showed superior tensile and yield strengths at high temperatures compared with commercial phosphorous bronze. This revised version was published online in November 2006 with corrections to the Cover Date.     

机械零部件用高强镁合金加工工艺与组织性能研究

针对Mg-Gd-Y合金塑性较差的问题,研究了固溶态和不同温度锻造加工态高强Mg-Gd-Y合金的组织与性能。结果表明,固溶态Mg-Gd合金的晶粒尺寸不均匀,平均尺寸约225μm;当锻造加工温度为440℃和410℃时,合金中第二相的数量较多,大量弥散分布的第二相的存在可以抑制动态再结晶的形成;随着锻造加工温度的降低,Mg-Gd合金的抗拉强度和屈服强度呈现逐渐升高的趋势,在锻造加工温度为470℃时,Mg-Gd合金的断后伸长率达到最大值19.2%,降低锻造加工温度至440℃和410℃时,断后伸长率反而有所降低;固溶态Mg-Gd合金的拉伸断口呈现脆性断裂的特征;锻造加工温度为500℃的拉伸断口呈现混合断裂特征,而锻造加工温度为410℃、440℃和470℃时Mg-Gd合金的断口都呈现为韧性断裂特征。