Effect of processing on microstructure and wear characteristics of an Al-4·5Cu-10Pb alloy

An Al-4·5Cu-10Pb alloy was processed by spray forming as well as impeller mixing followed by chill casting methods. The microstructure, mechanical properties and dry sliding wear characteristics of the alloy were evaluated. The spray formed alloy showed an equiaxed grain morphology with a uniform dispersion of lead particles in the matrix phase. In contrast a cellular-dendritic morphology of the primary phase was the characteristic feature of the alloy processed by impeller mixing and chill casting method. The spray formed alloy indicated its superior mechanical properties and low wear rate particularly at higher applied load and sliding velocity. The possible reason for this behaviour is discussed in the light of microstructure of the alloy and the nature of the worn out surfaces of the wear test specimens.     

Effect of secondary processing on the microstructure and wear behavior of spray formed Al–30Mg2Si–2Cu alloy

In the present work, Al–30Mg₂Si–2Cu alloy has been spray formed and subsequently hot pressed for densification. The alloy is then subjected to solutionizing and isothermal aging treatments. The microstructural features, hardness and wear behavior of spray formed and secondary processed alloys have been evaluated individually and compared with that of as-cast alloy. The microstructure of spray formed alloy showed refined and globular shaped primary Mg₂Si intermetallic particles and Al₂Cu precipitate particles uniformly distributed in Al matrix. The microstructure was refined further after hot consolidation. The microstructure after solution heat treatment appeared similar to that of the spray formed alloy but aging led to a further refinement in the microstructure compared to that of the hot pressed alloy. The evaluation of wear behavior of these alloys, under dry sliding condition, showed that the age hardened alloy exhibits maximum wear resistance and minimum coefficient of friction over the entire range of applied load (10–50 N) at a sliding speed of 2 ms⁻¹ followed by hot pressed, spray formed and solution heat treated alloys. The as-cast alloy showed the least wear resistance and highest coefficient of friction. Similar trend has been observed even in their hardness values too. The wear resistance of the alloys is discussed in light of their microstructural modifications induced during spray forming and subsequent secondary processing and also the topography of worn surfaces.     

离心雾化喷射成形工艺对锌基合金成形性和组织结构的影响

采用先进的离心雾化喷射成形技术研制具有良好耐磨性能的锌基合金环形件 ,研究在这种新工艺条件下锌基合金的成形性和组织特征 .研究结果表明 ,喷射沉积环形件的形状比较规整 ,厚度比较均匀 .沉积态材料组织细小、均匀 .工艺条件对喷射沉积锌基合金的质量有明显影响 .采用在基底和沉积层之间加过渡层金属的办法 ,可获得界面冶金结合良好的复合金属材料 .     

Wear characteristics of spray formed Al-alloys and their composites

In the present investigation, different Al based alloys such as Al–Si–Pb, Al–Si, Al–Si–Fe and 2014Al + SiC composites have been produced by spray forming process. The microstructural features of monolithic alloys and composite materials have been examined and their wear characteristics have been evaluated at different loads and sliding velocities. The microstructural features invariably showed a significant refinement of the primary phases and also modification of secondary phases in Al-alloys. The Pb particles in Al–Si–Pb alloy were observed to be uniformly distributed in the matrix phase besides decorating the grain boundaries. The spray formed composites showed uniform distribution of SiC particles in the matrix. It was observed that wear resistance of Al–Si alloy increases with increase in Pb content; however, there is not much improvement after addition of Pb more than 20%. The coefficient of friction reduced to 0.2 for the alloy containing 20%Pb. A sliding velocity of 1 ms⁻¹ was observed to be optimum for high wear resistance of these materials. Alloying elements such as Fe and Cu in Al–Si alloy lead to improved wear resistance compared to that of the base alloy. The addition of SiC in 2014Al alloy gave rise to considerable improvement in wear resistance but primarily in the low pressure regime. The wear rate seemed to decrease with increase in sliding velocity. The wear response of the materials has been discussed in light of their microstructural features and topographical observation of worn surfaces.     

Effect of magnesium on sliding wear performance of cast Al-8.3Fe-0.8V-0.9Si alloys

Abstract

The paper deals with the sliding wear behaviour of cast Al-Fe-V-Si alloys evaluated by 'pin on disc' tribometry. The alloys were castin cylindrical15 mm diameter metallic moulds from which 8 mmdiameter pins were machined. Volumetric wear loss and coefficient of friction were measured. Worn surfaces of the pins were examined by scanning electron microscopy. It was observed that by modifying the Al-Fe-V-Si alloys with Mg or Al-Mg master alloy the structure of Al₁₃Fe₄ precipitate changed from ten-armed star-like to hexagonal, rectangular, cuboidal, and other compact forms. The wear rate of the cast Al-Fe-V-Si alloys was much lower than that of eutectic Al-Si alloy. Modified Al-Fe-V-Si alloys exhibited lower wear rate and coefficient of friction than the unmodified Al-Fe-V-Si alloy. The wear rate decreased with increasing load for the modified Al-Fe-V-Si alloys. Both the wear rate and coefficient offriction were found to be load dependent. During wear extensive plastic deformation and work hardening occurred. The wear was shown to take place by delamination.     

Cast magnesium alloys for elevated temperature applications

The alloy development, microstructure, properties and uses of cast magnesium alloys for elevated temperature applications are reviewed. The alloying principles and strengthening mechanisms of magnesium are discussed to identify the potential alloy systems for elevated temperature applications in automotive and aerospace industries. It is concluded that the Mg-Zr family of sand cast alloys exhibit adequate mechanical properties at both ambient and elevated temperatures for aerospace applications, and Ca-modified sand cast AS41 alloy might provide a cost-effective alternative for the Zr-containing alloys. For diecasting applications, no current alloy systems meets the requirements of good high temperature properties, acceptable castability and low cost for critical automotive components, future development is especially needed in this area. Development of dispersion strengthened magnesium alloys and improvement of current Mg-Al-RE and Mg-Al-Si systems are the potential routes to expand diecast magnesium alloys to elevated temperature applications.     

Preparation of hot-pressed silicon-germanium ingots: Part II - Reduction of chill cast material

Nine different reduction techniques were evaluated for reducing Si-Ge chill cast alloys. Planetary ball milling with agate vessels and balls proved best for producing large quantities of high purity Si-Ge alloy powders. With the planetary ball mill Si-rich alloys were more difficult to reduce than Ge-rich alloys and the addition of dopant (boron or phosphorus) decreased the grinding time necessary for comparable particle size distributions.     

Microstructure evolution of spray deposited and as-cast 2195 Al-Li alloys during homogenization

In this paper,a comparative study on the spray deposited and as-cast 2195 alloy was carried out to reveal their microstructure evolutions and differences during the homogenization process.The dissolution of the secondary particles and the diffusion of solute were studied based on microstructure characterization and kinetics analysis.The precipitation behavior of Al3Zr dispersoids and its influence on recrystalliza-tion were investigated by using TEM and EBSD characterization.It was found that the large-size particles at triangular grain boundaries dissolve slower than the intragranular phases and other grain boundary phases.The required homogenization time depends on the dissolution processes of the large-size phases at grain boundaries.The size of grain boundary phases in the spray deposited alloy is much smaller than that in the as-cast alloy,so the homogenization time required for the spray deposited alloy is signifi-cantly shorter.Two-stage and ramp heating homogenization processes can promote the precipitation of Al3Zr dispersoids in the two alloys.In the spray deposited alloy,the dispersoids tend to precipitate at the positions of the T1 plates dissolved,which causes a non-uniform distribution and decreases the recrystallization resistance of the alloy.However,the distribution of the dispersoids in the as-cast alloy is more uniform after the homogenization,which brings a stronger inhibition on the recrystallization.According to the microstructural characterization and kinetics analysis results,it can be concluded that the homogenization with a slow ramp heating is suitable for the two 2195 alloys,and a shorter holding time can be used for spray deposited alloy,e.g.12 h at 500℃,while the holding time for the as-cast alloy is no less than 35 h at 500℃.     

铸造铝合金真空浸渗针孔修复组织及性能研究

本文采用真空浸渗技术,对铸造铝合金(ZL101A)针孔缺陷进行修复,并研究其修复后的综合性能.修复前后的试样分别进行显微组织及能谱分析、摩擦磨损实验、盐雾腐蚀试验等性能测试.研究结果表明:真空浸渗工艺后的铸铝合金表面针孔有效得到填充;摩擦磨损曲线更加平滑,摩擦系数0.61小于未浸渗试样的摩擦系数0.73;盐雾实验测试防腐等级由3级升到6级,表明真空浸渗修复工艺较好地提高了铸造铝合金的力学性能与防腐蚀性能.     

Sliding temperature and wear behaviour of cast Al–Si base alloy

Abstract

The influence of sliding interface temperature on friction and wear behaviour of eutectic (LM13) and hypereutectic (LM28) Al–Si base alloy in as cast and heat treated condition has been investigated. LM13 and LM28 alloys having nominal composition Al–12Si–1Ni–0.8Cu–0.6Mg and Al–17Si–1Ni–0.8Cu–0.6Mg used in this study. Wear and friction tests were performed under dry sliding conditions using a pin on disc type of friction and wear monitor with the data acquisition system conforming to ASTM G99 standard. It was found that sliding interface temperature has a close relation with wear and friction response of these alloys. Initial rise in temperature reduces the wear rate and as soon as a critical temperature (CT) is crossed, wear rate abruptly increases. The friction coefficient of both alloys first decreases with rise in temperature then subsequently increases beyond a certain temperature. The influence of temperature on wear behaviour in particular was found to be a function of alloy composition and heat treatment. For as cast LM28 alloy, the critical temperature (140°C) was found to be lower than that in the heat treated condition (180°C). A temperature–wear mechanism is proposed for these alloys.     

Microstructure and wear characteristics of spray formed and hot extruded Al–Si alloys

Abstract

The microstructural and wear properties of spray formed Al–6.5Si, Al–18Si and Al–18Si–5Fe–1.5Cu (wt-%) alloys have been investigated. The microstructure of the Al–6.5Si alloy exhibits the equiaxed grain morphology of the primary α-Al phase with eutectic Si at the grain boundaries. The size of the primary Si particulates in the Al–18Si alloy varied from 3 to 8 μm embedded in the eutectic matrix. Complex intermetallic phases such as β-Al₅ SiFe and δAl₄ Si₂ Fe are observed to co-exist with primary Si in the spray formed Al–18Si–5Fe–1.5Cu alloy system. The periphery of the preforms invariably showed pre-solidified particles with a large amount of interstitial pores. An extrusion ratio of 6 : 1 for these alloys led to drastic porosity reduction and extensive breaking of second phase particles. These microstructural features showed distinct variation in the wear behaviour and the coefficient of friction of the alloys. The Al–18Si–5Fe–1.5Cu alloy shows better wear resistance compared with the other two alloys, particularly at higher loads. The coefficient of friction shows a dependence upon the applied load. However, this becomes steady at higher loads. The wear behaviour of these alloys is discussed in light of the morphology of debris particles as well as that of the worn surfaces.     

TIC/7075铝基复合材料的磨损实验研究

采用原位反应喷射沉积法制备TiC/7075铝基复合材料,并在销一盘式磨损机损上进行摩擦磨损实验研究.通过TEM观察原位TiC颗粒的分布与形貌,并利用SEM观察沉积态组织磨损表面形貌.结果表明:复合材料的耐磨性和TiC颗粒含量及载荷有关,在低载荷(8.9N)状态下,材料的耐磨性随TiC颗粒含量的增加而增强,在高载荷(26...     

Effect of in-situ TiC particulate on the wear resistance of spray-deposited 7075 Al matrix composite

TiC reinforced 7075 Al matrix composites have been fabricated by a melt in-situ reaction spray deposition. The microstructures of spray-deposited alloys were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The dry sliding wear behavior of the alloys was investigated using a pin-on-disc machine under four loads, namely 8.9, 17.8, 26.7 and 35.6 N. It has been found that the wear behavior of the alloys was dependent on the TiC content in the microstructure and the applied load. At a lower load (8.9 N), with increasing TiC content, the wear rate of the alloy was decreased. At a higher loads (26.7, 35.6 N), a spray-deposited 7075 Al alloy exhibited superior wear resistance to the 7075/TiC composites.     

Microstructural control by spray forming and wear characteristics of a Babbit alloy

The effect of process variables during spray forming of a commercial Babbit alloy containing Pb74–Sn12–Sb11.5–Cu1.25–NiO.75–Cd0.3–As0.2 on its microstructure and wear characteristics were investigated. Variation in atomization gas pressure from 0.6 to 1.2 MPa and nozzle to substrate distance from 0.2 to 0.4 m revealed considerable change in the nature of porosity and microstructural features of the spray deposits. The process variables during spray deposition were optimized to achieve microstructural homogeneity and refinement in second phase particles of this alloy. The wear study of both the spray formed and as-cast alloy under an applied load of 10 to 70 N and sliding velocity of 0.2 to 1.5 ms-1 indicated two distinct regimes of mild and severe wear. In both the regimes, the spray-formed alloy consistently indicated a low wear rate compared to that of the as-cast alloy. In addition, the mild wear regime of the spray-formed alloy was extended to higher load and sliding velocity. Wear characteristics of the spray formed alloy is discussed in light of its microstructural features induced during spray deposition processing.     

Heat transfer during solidification of chemically modified Al–Si alloys around a copper chill

Abstract

The solidifying metal/chill contour will significantly affect the boundary heat transfer coefficients, and solidification modellers should be aware of the casting conditions for which the heat transfer coefficients are determined. The previous work carried out on solidification of Al–Si alloys in a metallic mould and solidification against bottom/top chills has shown that modification and chilling have synergetic effect resulting in a significant increase in the heat flux transients at the casting/chill interface. In the present work, the heat transfer during solidification of unmodified and chemically modified Al–Si alloys around a cylindrical copper chill was investigated. Heat flux transients were estimated using lumped heat capacitance method. Lower peak heat flux was obtained with chemically modified alloy. This is in contrast to the results reported for alloys solidifying against chills and in metallic moulds. The chill thermal behaviour and heat transfer to the chill material when surrounded by modified and unmodified alloys were explained on the basis of the decrease in the degree of undercooling in the case of modified alloy as compared to unmodified alloy and the change in contact condition and shrinkage characteristics of the alloy due to the addition of chemical modifiers.     

过喷粉热压烧结Al50Si50合金的摩擦磨损性能研究

利用喷射沉积过喷粉热压烧结制备了 Al50Si50合金,用 MMW-1型立式万能摩擦磨损试验机来测试不同热压烧结工艺条件下所制备合金的摩擦磨损性能,用金相显微镜和扫描电镜观察其组织和磨损形貌,并分析其磨损机理。研究结果表明：随着烧结压力增加、温度升高、时间延长,热压烧结试样的密度和致密度增加,摩擦系数和比磨损率降低。试样的磨损过程中存在磨料磨损和黏着磨损两种机制,且由于摩擦磨损过程中 Si 相的存在导致材料以磨料磨损为主。     

Structural and wear properties of sputter-deposited laves intermetallic alloy

An adhesive wear-resistant alloy, with a type MgZn₂ close-packed hexagonal Laves intermetallic phase to promote abrasive wear resistance, was d.c. sputter deposited onto steel substrates at temperatures in the range 20–800°C using a hollow cathode sputtering device. Coating thicknesses were in the range 20–60 μm. Coating structures were examined by preparing metallographic cross sections and by X-ray diffraction. The wear properties of coated and uncoated steel rings (hardness, Rc 60), sliding against blocks of cast iron, a soft steel, a tool steel, a cobalt alloy, WC-Co and a cast form of a different Laves phase intermetallic alloy, were compared in both room air and a non-lubricating liquid. Coatings deposited at a substrate temperature of about 800 °C exhibited the Laves phase diffraction profiles. Coatings deposited at lower temperatures exhibited fine-grained (amorphous type) X-ray diffraction patterns. Metallographic cross sections revealed a dense columnar structure. Microhardnesses were about 900 kg mm^-2 (KHN) independent of substrate temperature. In room temperature air with no lubricant, the wear properties of the rings with the sputter-deposited coatings were superior to the uncoated ones when sliding against the tool steel, cobalt alloy and cast Laves phase blocks. No significant improvement was seen for sliding against the cast iron, soft steel and WC-Co blocks. With a poor lubricant and higher normal forces, the coated and uncoated rings performed well against the Laves phase and tool steel blocks; however, the coated rings were generally inferior for the other couples tested.     

Sliding Wear Behavior of Plasma Sprayed Zirconia Coating on Cast Aluminum against Silicon Carbide Ceramic

1.IntroductionPlasma-sprayed zirconia ceramic coating is widelyused for heat engines,gas turbine parts,aerospace seals,and lubrication systems,because of its special mechani-cal,chemical,and thermal properties[1].Previous stud-ies of the friction and wear patterns of zirconia andits coatings have been reported[2~14].The wear be-havior of zirconia ceramics seemed to be very sensi-tive to the structure of the material,and to test pa-rameters such as temperature,environment,and slid-ing speed[2].…     

Structure, mechanical and tribological properties of diamond-like carbon films on aluminum alloy by arc ion plating

The low hardness and poor tribological performance of aluminum alloys restrict their engineering applications. However, protective hard films deposited on aluminum alloys are believed to be effective for overcoming their poor wear properties. In this paper, diamond-like carbon (DLC) films as hard protective film were deposited on 2024 aluminum alloy by arc ion plating. The dependence of the chemical state and microstructure of the films on substrate bias voltage was analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy. The mechanical and tribological properties of the DLC films deposited on aluminum alloy were investigated by nanoindentation and ball-on-disk tribotester, respectively. The results show that the deposited DLC films were very well-adhered to the aluminum alloy substrate, with no cracks or delamination being observed. A maximum sp³ content of about 37% was obtained at −100 V substrate bias, resulting in a hardness of 30 GPa and elastic modulus of 280 GPa. Thus, the surface hardness and wear resistance of 2024 aluminum alloy can be significantly improved by applying a protective DLC film coating. The DLC-coated aluminum alloy showed a stable and relatively low friction coefficient, as well as narrower and shallower wear tracks in comparison with the uncoated aluminum alloy.     

Improved properties of A319 aluminum casting alloy modified with Zr

The beneficial effects of 0.15 wt.% Zr addition on mechanical properties and wear resistance of A319 aluminum casting alloy were investigated. The cast alloys were given a solutionizing treatment followed by artificial aging in the temperature range 175 to 235 °C for different period of times. Mechanical properties and wear behavior of the Zr-containing material were determined and compared to those of the base A319 alloy in both as-cast and age-hardened conditions. It is shown that minor addition of Zr results in the precipitation of Al₃Zr particles in the aluminum matrix. These particles are stable upon heating due to the low solubility of zirconium in aluminum matrix. The main effects of such particles are an increase in hardness, strength, quality index and wear resistance. This is very promising where these aluminum cast alloys are to be used at relatively high temperatures.