A comparative study on abrasive wear behavior of semisolid–liquid processed Al–Si matrix reinforced with coated B4C reinforcement

A comparative study on abrasive wear behavior of the sol?Cgel coated B₄C particulate reinforced aluminum metal matrix composite has been carried out in the present investigation. In general, composites offer superior wear resistance as compared to the alloy irrespective of applied load and B₄C particles volume fraction. This is primarily due to the presence of the hard dispersoid which protects the matrix from severe contact with the counter surfaces, and thus results in less wear, lower coefficient friction and temperature rise in composite as compared to that in the alloy. The wear sliding test disclosed that the weight loss of the coated B₄C reinforced composites decreases with increasing volume fraction of B₄C particulates. The wear rate in all the samples increases marginally with applied load prior to reaching the critical load. It is ascribed to the increase in fracture of reinforcement, the penetration of hard asperities of the counter surface into the softer pin surface and micro cracking tendency of the subsurface. After the critical load there is a transition from smooth linear increase wear rate to sudden increase in wear rate. This is attributed to the significantly higher frictional heating and thus the localized adhesion and softening of the surface with the counter surface.     

6061Al/Al2O3金属基复合材料组织和性能

以6061Al作为基质材料,利用液体冶金的搅拌铸造技术及挤压法制备Al₂O₃颗粒增强的金属基复合材料,选取6061Al添加3种质量分数为5%、10%和15%的Al₂O₃为研究对象,以改善6061Al/Al₂O₃复合材料的力学性能。通过SEM分析表明,Al₂O₃颗粒在6061Al金属基体中的分布相当均匀;由X射线衍射试验结果显示,复合材料中只有6061Al和Al₂O₃,且不会影响结晶性及6061Al的组织结构型态。试验结果表明,随着Al₂O₃添加量增加至15%,6061Al/Al₂O₃复合材料的硬度和抗拉强度均有较大提高,但伸长率略有下降,由于材料孔隙率的提升,致密度下降,从而引起材料的硬度略微下降;分析磨损量与Al₂O₃添加量及磨损率与滑动距离的关系,结果显示商用6061Al的磨损率最大,而6061Al/Al₂O₃(15%)复合材料的磨损量最小,并且磨损率最低,这是由于在6061Al中加入Al₂O₃颗粒,Al₂O₃颗粒的存在可以减少磨粒对基体的犁削作用,有效提高基体的耐磨性。深入探讨Al₂O₃颗粒增强的金属基复合材料,发现颗粒增强体以很细的粉末(一般在20 μm以下)加入到金属基中起到提高硬度、强度和耐磨性的作用;然而,Al₂O₃添加量越来越大时,其对6061Al系列材料的硬度、强度和耐磨耗性等性能将起到负面作用。     

Effect of distribution of B4C on the mechanical behaviour of Al-6061/B4C composite

In this work, the effect of mixing parameters on the distribution of B₄C in 6061-Al alloy and its correlation with mechanical behaviour was studied. 6061-Al alloy powder was mixed with 10 mass-% B₄C powder in a ball mill and powder rotator mixer by varying mixing time from 1 to 5?h. Mixing was performed in both wet and dry conditions in a ball mill while only dry condition was used in the powder rotator mixer. The green compacts were sintered at 630°C. The quadrat method was used to quantify the distribution of B₄C particles in the microstructures of sintered Al/B₄C composite. The results showed that the distribution was improved with mixing time but the density, hardness and compression strength of Al/B₄C composites were reduced with time during ball milling. On the other hand, the distribution of reinforcement, density, hardness and compressive strength of Al/B₄C composites was improved with mixing time in the powder rotator mixer.     

Investigation of Microstructure,Mechanical and Wear Behaviour of B<Subscript>4</Subscript>C Particulate Reinforced Magnesium Matrix Composites by Powder Metallurgy

In the present study, magnesium and magnesium matrix composites reinforced with 10, 20 and 30 wt% B₄C particulates were fabricated by powder metallurgy using hot pressing technique. The microstructure, mechanical properties and wear behaviour of the samples were investigated. Microstructure characterization showed generally uniform distribution of B₄C particulates. XRD investigations revealed the presence of Mg, B₄C and MgO phases. The mechanical properties of the investigated samples were determined by hardness and compression tests. Hardness and compressive yield strength significantly increased with increasing B₄C content. The reciprocating wear tests was applied under loads of 5, 10 and 20 N. Wear volume losses decreased with increasing B₄C content. Abrasive and oxidative wear mechanisms were observed.     

Electron and laser beam welding of high strain rate superplastic Al-6061/SiC composites

The welding characteristics of a fine-grained 6061 Al and three 6061/1, 5, and 20 pct SiC composites under high energy electron beam welding (EBW) and laser beam welding (LBW) were examined. The three composites exhibited high strain rate superplasticity (HSRS). The 6061 Al was more readily welded by EBW than by LBW, and the situation was reversed in the reinforced composites. In the reinforced composites, the fusion zone contained the once fully melted matrix and fully reacted SiC, and the heat affected zone (HAZ) contained the partially melted matrix and nearly unreacted SiC. This effect was particularly apparent in the 20 pct SiC composite. With increasing SiC content from 0 to 20 pct, the reflection of the laser beam decreased, and the melt viscosity increased due to the increasing amount of Al₄C₃ compounds. For the HSRS fine-grained 6061/20 pct SiC composite, there formed a sharp V-notch under EBW. The high viscosity or low fluidity of the melt inside the fusion zone of 6061/20 pct SiC resulted in incomplete backfill and notch formation. The postweld mechanical performance and joint efficiency both became seriously degraded. The original fine structures in the HSRS composites could not be restored after welding.     

High-temperature wear and deformation processes in metal matrix composites

Dry-sliding wear behaviors of a particulate-reinforced aluminum matrix composite 6061 Al-20 pet A1₂O₃ and an unreinforced 6061 Al alloy were investigated in the temperature range 25 °C to 500 °C against a SAE 52100 bearing steel counterface. Experiments were carried out at a constant sliding speed of 0.2 m·s^- at different test loads. The deformation behavior of the materials was studied by performing uniaxial compression tests in the same temperature range as the wear tests. Both alloys showed a mild-to-severe wear transition above a certain test temperature. In the mild wear regime, the wear rate and the coefficient of friction of the unreinforced 6061 Al decreased slightly with temperature, but the temperature had almost no effect on the wear rate and the coefficient of friction of the 6061 Al-20 pet Al₂O₃ in the same regime. Particulate reinforcement led to an increase in the transition temperature and a 50 to 70 pet improvement in the wear resistance in the severe wear regime. This was attributed to the formation of tribological layers consisting of comminuted A1₂O₃ particles at the contact surface. High-temperature compression tests showed that the flow strength of 6061 Al-20 pet A1₂O₃ and 6061 Al decreased monotonically with temperature and both alloys exhibited a work-softening behavior at temperatures higher than the inflection point on the flow stressvs temperature curves. The logarithmic maximum stressvs reciprocal temperature relationship was not linear, indicating that the deformation processes were too complicated to be characterized by a single activation energy over the whole temperature range. For the range of 250 °C to 450 °C, the activation energy for deformation was estimated to be 311 kJ·mol^-1; for both the matrix alloy and the composite. Severe wear proceeded by thermally activated deformation processes involving dynamic recrystallization along a subsurface strain gradient. A power-Arrhenius type relationship was found to describe well the observed dependence of severe wear rates on the applied load and temperature. This relationship was used to calculate an apparent activation energy for wear of 87 kJ·mol^-1 for the particulate-reinforced composite and 33 kJ·mol^-1 for the matrix alloy. The wear regimes at elevated temperatures are represented in a deformation mechanism map and the relationship between high-strain deformation processes and severe wear are discussed.     

Effects of Ni60WC25 powder content on the microstructure and wear properties of WC<Subscript>p</Subscript> reinforced surface metal matrix composites

The vacuum evaporative pattern casting technique was used to fabricate WC_p reinforced surface metal matrix composites in order to study the effects of Ni60WC25 powder content on the microstructure and wear properties of it. The results showed that the Ni60WC25 powders weakened the stability of WC particles and reacted with metal matrix at the interfacial regions in the composite. Diffusion kinetics and Gibbs free energy were calculated from the interactions between WC particles and matrix. It was found that adding 35 vol% Ni60WC25 alloy powder to composites led to the formation of Fe₃W₃C phases and complete dissolution of WC particles. The wear properties of composites with different Ni60WC25 alloy powder content were tested by the MLD-10 type tester. WC particles and Fe₃W₃C phases could protect the matrix and the matrix could support WC particles and Fe₃W₃C phases during wear processing.     

Synergistic effects of wear and corrosion for Al2O3 particulate-reinforced 6061 aluminum matrix composites

Wear corrosion of alumina particulate-reinforced 6061 aluminum matrix composites in a 3.5 wt pct NaCl solution with a revised block-on-ring wear tester has been investigated. The studies involved the effects of applied load, rotational speed, and environments (dry air and 3.5 pct NaCl solution) on the wear rates of materials. Also various specimens with Al₂O₃ volume fractions of 0, 10, 15, and 20 pct were employed in this work. Electrochemical measurements and electron micrographic observations were conducted to clarify the micromechanisms of wear corrosion in such metal matrix composites. Experimental results indicated that the wear rate of monolithic 6061 Al in either dry wear or wear corrosion was reduced by adding alumina reinforcements. However, the effect of volume fraction on wear rate is only minor in dry wear, while it is significant in the case of wear corrosion. Wear-corrosion tests also showed that the corrosion potential shifted to the active side and the current density for an applied potential increased with the decrease of Al₂O₃ volume fraction in the materials and the increase in applied load and rotational speed. Although the incorporation of reinforcement in these aluminum matrix composites was deterimental to their corrosion resistance, the influence on wear corrosion was favorable.     

Interfacial characteristics for brazing of aluminum matrix composites with Al-12Si filler metals

Discussions concerning the interfacial reactions and characterizations in brazing aluminum matrix composites are documented in this study. Joints of alumina particulate reinforced 6061 aluminum matrix composites were made using an Al-12 (wt pct) Si filler metal by vacuum brazing. The resulted maximum bonding strengths were 75.4, 81.5, and 71.8 MPa for 10, 15, and 20 vol pct alumina reinforcement, respectively. The microstructural examinations revealed that the bonding strength was strictly related to the reinforced alumina particles and the reaction products presented at the joint interfaces. During brazing, Mg segregated at the joining interface and alumina/6061 Al interface. Further, reactions between alumina and 6061 Al matrix resulted in the formation of Mg-rich phases, such as MgAl₂O₄ and MgO, near the joining interface and the alumina reinforcement. The Si in the filler material penetrated into the metal matrix composites (MMCs) matrix and segregated at the alumina/6061 Al interfaces. This phenomenon can be confirmed by a joint between two alumina bulk specimens.     

Study of 6061-Al2O3p composites produced by reciprocating extrusion

A reciprocating extrusion process was developed to consolidate 6061-Al₂O_3p composites from mixed powders. The 6061 alloy powder was first dehydrated in a vacuum chamber at 450 °C and then mixed with 12.5 μm Al₂O₃ powder in various volume fractions: 0, 5, 10, 20, and 30 pct. The mixed powders were hot pressed at 300 °C under a pressure of 300 MPa and finally extruded reciprocatingly 14 times at 460 °C. The results show that the composites were fully densified, with no sign of pores or oxide layers observable in the optical microscope. The Al₂O₃ particles were distributed uniformly in the matrix. As compared with 6061 alloys, the composites demonstrated a smaller precipitation hardening and elongation, but exhibited a higher Young’s modulus and a larger work hardening capacity. The degradation of precipitation hardening was due to the loss of Mg, which reacts with Al₂O₃ to form MgAl₂O₄. The large work-hardening capacity is attributable to the incompatibility between Al₂O₃ and the matrix, which possibly generates more dislocations to harden the matrix. The composites had much higher friction coefficients and greater wear resistances than the 6061 alloy against steel disc surface. The friction coefficient of the 6061-30 vol pct Al₂O_3p composite was double that of the 6061 alloy and the wear resistance was 100-fold. As compared with similar composites reported previously, these composites possessed much higher elongation at the same strength level. A 30 vol pct Al₂O_3p still displayed an elongation of 9.8 pct in the T6 condition. All of these improvements are attributed to the merits, including full densification of the bulk, uniform dispersion of the Al₂O₃ particles in the matrix, and strong binding between the Al₂O₃ particles and the matrix resulting from reciprocating extrusion.     

Wear behaviour of Fe3 Al intermetallic particle reinforced PM based iron metal matrix composites

Abstract

The wear behaviour of unreinforced and reinforced PM based iron metal matrix composite, the latter containing 10 and 20 vol.-% nano sized Fe₃Al intermetallic particles, was studied as a function of sliding distance under two different loads and dry lubricated conditions. The intermetallic Fe₃Al nanoparticles were prepared by mechanical alloying and used as particle reinforcement with 10 and 20 vol.-% in the matrix. The processing of the composites included mixing and cold compaction followed by sintering at 1120°C. The influence of Fe₃Al additions on the dry sliding wear behaviour was studied at loads 20 and 40 N over sliding distances 2160, 3240, 4320 and 6480 m. The study showed that the composite exhibited a lower wear rate than that of the unreinforced matrix and the wear rate was influenced by the volume percentage of Fe₃Al particles. It is understood that iron aluminide reinforcement has a beneficial effect on the wear properties. Delamination and microcutting were the chief mechanisms of wear for the composites.     

The influence of the coating technique on the high cycle fatigue life of alumina coated Al 6061 alloy

The primary objective of this study is to evaluate the influence of coating technique on the high cycle fatigue of an Al6061 alloy. Towards this purpose, Al6061 alloy fatigue samples have been coated with Al₂O₃ utilising the detonation spray, air plasma spray, micro arc oxidation and hard anodizing techniques. The high cycle fatigue life of these coated samples has been evaluated over a range of alternating stress values and compared with the fatigue life of the uncoated Al6061 alloy. It is observed that the detonation spray coated sample exhibits a higher fatigue life than the uncoated sample. In contrast, the samples coated using the other techniques exhibit poorer fatigue life compared to the uncoated sample especially at lower alternating stress values. These results have been explained on the basis of the nature of the coating-substrate interface which is strongly determined by the coating technique used to deposit the Al₂O₃ coatings.     

Dry sliding wear behaviour of a novel 6351 Al-Al4SiC4 composite at high loads

In this research work the dry sliding wear behaviour of 6351 Al alloy and 6351 Al based composites possessing varying amount of (2–7 vol%) insitu Al₄SiC₄ reinforcement was investigated at low sliding speed (1?m?s^?1) against a hardened EN 31 disk at higher loads (44 N and 68.7 N). In general, at higher loads, the wear mechanism involved microcutting and microploughing abrasion. In most occasions, Al₄SiC₄ reinforced 6351 Al based composites exhibited much higher wear rate (lower wear resistance) than the unreinforced 6351Al alloy. This was mainly attributed to the removal of reinforcement particle through microcutting abrasion process that resulted in cavitation and subsequent microploughing abrasion for rapid removal of material from surface. This is on contrary to the author's previous research work, where at lower loads (24.5 N or below), Al₄SiC₄ particles stood tall to enhance wear resistance of 6351 Al-Al₄SiC₄ composite.     

Study of Tribological and Mechanical Properties of A356–Nano SiC Composites

In the present investigation, the microstructural, wear, tensile and compressive properties of Al?C7Si alloy matrix nano composites have been discussed. It is noted that the composites contain higher porosity level in comparison to the matrix and increasing amount of porosity is observed with the increasing volume fraction of the reinforcement phase in the matrix. The wear sliding test disclosed that the wear resistance of the nano SiC reinforced composites is higher than that of the unreinforced alloy. It is believed that the presence of SiC particles could shield the matrix and silicon phase from directly experiencing the applied load from the counterface. It was revealed that the presence of nano-SiC reinforcement also enhanced the hardness, tensile and compressive yield strength of Al?C7Si alloy which can be attributed to small particle size and good distribution of the SiC particles and grain refinement of the matrix. The highest yield strength and UTS was obtained by the composite with 3.5?vol% SiC nano-particles. The results show that the addition of nano-particles reduces the elongation of A356 alloy.     

Statistical Analysis of Tribological Properties of Aluminum Matrix Composites Using Full Factorial Design

This work describes the tribological properties of mono AA6061-10 wt% B₄C and hybrid AA6061-10 wt% B₄C-7.5 wt% Gr composites which could be used as a potential substitute for aluminum alloys used in automotive engines. The tribological experiments are performed as per the experimental scheme designed using full factorial design. The results suggest that the wear loss increases with applied load and sliding distance and the friction coefficient increases with increase in applied load. Further, the ANOVA analysis reveals the statistically and physically significant factors which influence the wear loss and friction coefficient. Formation of Gr-rich tribolayer causes reduction in the wear loss and friction coefficient for hybrid composites compared to the mono ones.     

Mechanical Properties and Tribological Behavior of Al6061–SiC–Gr Self-Lubricating Hybrid Nanocomposites

In the present investigation, a newly fabricated Al6061 reinforced with various quantity (0.4–1.6 wt%) of nano SiC in steps of 0.4 and fixed quantity (0.5 wt%) of micro graphite particle’s hybrid nanocomposites were prepared by ultrasonic assisted stir casting method. The influence of nano SiC and graphite content on the mechanical and tribological properties of Al6061 hybrid nanocomposites were studied. The pin-on-disc equipment was used to carry out experiment at 10–40 N applied load, 0.5 m/s sliding speed and 1000 m sliding distance. The Al/SiC/Gr hybrid nano-composite and matrix alloy wear surfaces were characterized by FESEM equipped with an EDS, 3D profilometer to understand the wear mechanisms. The results of Al/SiC/Gr self-lubricating hybrid nano-composites showed improved wear resistance than the Al6061 matrix alloy. The co-efficient of friction of Al/SiC/Gr hybrid nano-composites were lower than those of the unreinforced alloy at various applied load. Compared to matrix alloy, the surface roughness of Al/SiC/Gr hybrid nano-composites had significantly reduced to 66% at low load and 75% at high load. Self-lubricating Al/SiC/Gr hybrid nanocomposites showed superior surface smoothness compared to matrix alloy.     

High-temperature deformation of 6061 Al

The creep behavior of powder metallurgy (PM) 6061 Al, which has been used as a metal matrix alloy in the development of discontinuous silicon carbide reinforced aluminum (SiCAl) composites, has been studied over six orders of magnitude of strain rate. The experimental data show that the steady-state stage of the creep curve is of short duration; that the stress dependence of creep rate is high and variable; and that the temperature dependence of creep rate is much higher than that for self-diffusion in aluminum. The above creep characteristics are different from those documented for aluminum based solid-solution alloys but are similar to those reported for discontinuous SiCAl composites and dispersion-strengthened (DS) alloys. Analysis of the experimental data shows that while the high stress dependence of creep rate in 6061 Al, like that in DS alloys, can be explained in terms of a threshold stress for creep, the strong temperature dependence of creep rate in the alloy is incompatible with the predictions of available threshold stress models and theoretical treatments proposed for DS alloys.     

Interfacial Microstructure in a B4C/Al Composite Fabricated by Pressureless Infiltration

In this work, B₄C particulate-reinforced Al composite was fabricated by a pressureless infiltration technique, and its interfacial microstructure was studied in detail by X-ray diffraction as well as by scanning and transmission electron microscopy. The B₄C phase was unstable in Al melt during the infiltration process, forming AlB₁₀-type AlB₂₄C₄ or Al_2.1B₅₁C₈ as a major reactant phase. The Al matrix was large grains (over 10 μm), which had no definite orientation relationships (ORs) with the randomly orientated B₄C or its reactant particles, except for possible nucleation sites with { 011}_{\textB4 \textC} \{ 011\}_{{{\text{B}}_{4} {\text{C}}}} almost parallel to {111}_Al at a deviation angle of 1.5 deg. Both B₄C–Al and reactant–Al interfaces are semicoherent and free of other phases. A comparison was made with the SiC/Al composite fabricated similarly by the pressureless infiltration. It was suggested that the lack of ORs between the Al matrix and reinforced particles, except for possible nucleation sites, is the common feature of the composites prepared by the infiltration method.     

The effect of participate reinforcement on the sliding wear behavior of aluminum matrix composites

The aim of the present investigation is to characterize the friction and wear behavior of aluminum matrix composites reinforced with particulates of SiC, TiC, TiB₂, and B₄C. Sliding wear tests were conducted at two loads (80 and 160 N) using a pin-on-disc apparatus and under dry conditions. The results of the investigation indicate that the coefficient of friction of the composites is about 30 pct lower than that of pure aluminum, while the wear rates of the com- posites are lower by a factor of about 3 and 100 at loads of 80 and 160 N, respectively. The type and size of the reinforcement have a negligible influence on the wear rate and the coefficient of friction of the composites. However, the volume fraction of the reinforcement has a marginal influence on the wear rate. Though the coefficients of friction and the wear rates of the com- posites were broadly similar, the Al-TiC composite alone exhibits a somewhat higher wear rate. The above results of the present investigation have been rationalized on the basis of the inverse rule of mixtures and the existing models for friction and wear.     

Microscopic examination of the interface region in 6061-Al/SiC composites reinforced with as-received and oxidized SiC particles

Aluminum (6061) matrix composites reinforced with different SiC particles were processed. Black SiC particles were used in their as-received form or after artificial oxidation, leading to a 50-nm-thick SiO₂ layer surrounding the SiC particles. The manufacturing route used was the compocasting technique, which allows maintenance of the semisolid slurry at relatively low temperatures (<650 °C) during the incorporation of the reinforcement. Before squeeze casting, the liquid alloy is held at 700 °C for 5 to 10 minutes. The interface between the aluminum matrix and SiC was characterized by transmission electron microscopy (TEM). Results show that no reaction takes place during compocasting between the as-received SiC particles and the molten aluminum. This is a consequence of the low temperatures and short holding times in the liquid state of the 6061 alloy, possible with this process. Prolonged holding at 800 °C of this material leads to extensive formation of A1₄C₃. In the case of artificially oxidized SiC particles, the SiO₂ layer surrounding the SiC particles reacts with the molten Al-Mg-Si alloy to produce MgAl₂O₄. However, the amount of Mg from the base alloy lost to form this spinel phase is not sufficient to prevent age hardening of the material.