Al MMC Research Articles

Characteristics of hole formation during laser drilling of SiC reinforced aluminium metal matrix composites

The objective of this research is to investigate the hole formation mechanism during millisecond pulsed laser drilling of aluminium metal matrix composites reinforced with silicon carbide particles (Al MMC). The main focus of this paper is to provide an insight into the fundamental principles that govern the millisecond laser drilling of Al MMC, including the laser-material interaction and the subsequent melt ejection, so as to achieve a high quality and high-speed drilling process. The experimental results demonstrate that the laser drilling mechanism of SiC particle reinforced MMCs are different from the mechanisms observed in laser drilling of non-reinforced metals and alloys. High-speed videos and finite element analysis based models were used to study the mechanism of material removal. The SiC particles within the MMC are not melted and are ejected undamaged, along with the molten low melting point matrix materials, which makes the drilling process more efficient and enables drilling with a lower laser power compared to monolithic materials.

Laser Based Machining of Aluminum Metal Matrix Composites

Aluminium metal matrix composites (Al MMC) are a relatively new type of material which combine lightweight metallic matrices (aluminium) with hard ceramic reinforcements (like alumina fibre or silicon carbide particles). Al MMCs have excellent potential in various applications from automotive to aerospace; however, their use is currently limited due to their low machinability. Conventional laser processes such as the laser drilling or cutting of monolithic materials (metals/alloys) are well-established processes. However, conventional laser processing of anisotropic materials like metal matrix composites is challenging due to the immense differences in the chemical and physical properties of the matrix and reinforcement. Over the last decade, nanosecond laser based water jet guided (WJG) machining has securely established itself as a novel laser based machining process, especially for the machining of non-monolithic materials like composites. The main investigation of this paper is centred on understanding the performance of WJG laser and conventional high power fibre laser machining of Al MMC. Laser machining of both fibre-based and particle-based Al MMC has been investigated (Al2O3 Fibre–Al MMC; SiC Particle–Al MMC). The WJG laser machining results were compared with the results from conventional long pulse/continuous wave laser process.

Enhanced Corrosion Resistance of SiC<sub>p</sub>/ 2009 Al by Cerium and Lanthanum Conversion Treatment

The present study investigates the effect of lanthanide chlorides conversion coatings on the corrosion response of the 2009 Al alloy and SiCp reinforced 2009 Al MMCs. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies showed that the localized corrosion resistance increased after treatments with solutions having various combinations of CeCl3.7H2O and LaCl3.7H2O, with maximum increase noticed for 5000ppm CeCl3.7H2O. It was found that the protection degree effect obtained under similar coating conditions for 25 vol.% SiCp/2009 Al was relatively higher than 15vol.% SiCp/ 2009 Al MMC, but both of them were less than that of the unreinforced alloy. Scanning electron microscopy (SEM) accompanied with energy dispersive spectroscopy (EDS) analysis revealed the deposition of Ce and/ or La oxides/ hydroxides on cathodic intermetallics/ SiCp and the existence of crevices at the SiCp/ matrix interfaces. X-ray photoelectron spectroscopy (XPS) results indicated that Ce was incorporated as Ce3+ and Ce4+ species in the coatings.

Wear resistance performance of AlCrN and TiAlN coated H13 tools during friction stir welding of A2124/SiC composite

Tool wear during friction stir welding (FSW) of hard particulate reinforced aluminum metal matrix composites (Al MMCs) are more prominent due to the tool interaction with the particulates at high strain rate. Considering the excellent mechanical and wear resistance properties of cathodic arc PVD coatings, they are expected to abate the wear of tools during FSW of Al MMCs. Hence, it is the aim of this study to investigate the contribution of cathodic arc PVD deposited AlCrN and TiAlN coatings in alleviating tool wear during FSW of Al MMCs. AlCrN and TiAlN coated H13 FSW tools were used to butt weld 8 mm thick aluminum alloy 2124 reinforced with 17 vol% SiC of 3 μm particle size. Interestingly, the coated tools exhibited significant improvement in wear resistance of about 92 and 80%, respectively, over the bare H13 tool. Over 97% reduction in the wear of the FSW tool was recorded during the plunging stage with the use of the coated tools. Additionally, AlCrN and TiAlN coated tools considerably improved the surface finish of the welded Al MMC. The coated tools demonstrated superior wear resistance due to the improved scratch crack resistance, high mechanical and oxidation resistance properties of the coatings. Dominant wear mechanisms on AlCrN and TiAlN coated tools were abrasive erosion and chipping off by sharp and hard SiC particles while severe striation and oxidation characterized the wear mechanism of the bare tool. The use of these coatings did not deteriorate the weld properties, rather some improvement in the hardness of the nugget zone was observed due to the characteristic dynamic stirring and refinement of the Al matrix and SiC particles.

Mechanical and tribological behaviour of nano scaled silicon carbide reinforced aluminium composites

ABSTRACTThis work assesses the impact of the presence of Nano scaled silicon carbide on the Mechanical & Tribological behavior of aluminium matrix composites. Aluminium matrix composites containing 0, 0.5, 1, 1.5, 2 and 2.5 wt.%-nano scaled silicon carbide was set up by a mechanical stirrer. The trial comes about to demonstrate that the inclusion of Nano silicon carbide brings about materials with progressively high elastic modulus and likewise brings about expanded brittle behavior, fundamentally lessening failure strain. Shear modulus and flexural shear modulus likewise increases with silicon carbide increase. The presence of Nano scaled silicon carbide in the aluminium matrix diminishes subsurface fatigue wear and increases wear resistance, because of silicon carbide lubricant activity. Wear testing, microstructure & morphological, density & void testing, hardness, flexural and tensile test of the readied composites were investigated and outcomes were analyzed which demonstrated that including nano-SiC in aluminum (Al) matrix increased wear resistance, tensile strength, and 2 wt. % of nano scaled SiC for Al MMC indicated maximum wear resistance, tensile strength, and an optimum balanced mix of both Tribological and Mechanical properties. Microstructural observation uncovered uniformand homogeneous distribution of SiC particles in the Al matrix.

Mechanical performance of particulate-reinforced Al metal-matrix composites (MMCs) and Al metal-matrix nano-composites (MMNCs)

The metal-matrix composites/nano-composites (MMCs/MMNCs) reinforced with hard ceramic particulates have received a tremendous attention due to their potential improvements in physical and mechanical performances. In the present work, we have comprehensively collected currently available experimental data sets of Al-based MMCs/MMNCs and have carried out thorough analyses to quantitatively address the impacts of the reinforcement volume fractions, reinforcement particle sizes, and metal-matrix grain sizes on their mechanical properties including the yield strength, ultimate strength, and strain to failure of composites. We also performed a quantitative analysis on the strengthening mechanisms of Al MMNCs to reveal that the grain refinement can play a major role in increasing the strength of composites. Al-based MMC or MMNC materials generally exhibited an indirect relationship between the strength increase and strain-to-failure increase. The results include a critical comparison for the mechanical performance of particulate-reinforced composites for both pure and alloyed Al matrices to elucidate the contemporary status of Al MMC and MMNC materials.

Microstructure, Mechanical and Surface Morphological Properties of Al5Ti5Cr Master Alloy as Friction Material Prepared by Stir Die Casting

Metal matrix composite offers outstanding properties for better performance of disc brakes. In the present study, the composite of AlTiCr master alloy was prepared by stir die casting method. The developed material was reinforced with (0–10 wt%) silicon carbide (SiC) and boron carbide (B4C). The effects of SiC reinforcement from 0 to 10 wt% on mechanical, microstructure and surface morphological properties of Al MMC was investigated and compared with B4C reinforcement. Physical properties like density and micro Vickers hardness number show an increasing trend with an increase in the percentage of SiC and B4C reinforcement. Mechanical properties viz. UTS, yield strength and percentage of elongation are improved with increasing the fraction of reinforcement. The surface morphology and phase were identified from scanning electron microscopy (SEM) and X-ray diffraction analysis and the oxidized product formed during the casting was investigated by Fourier transformation infrared spectroscopy. This confirms the presence of crystallization of corundum (α-Al2O3) in small traces as one of the alumina phases, within casting sample. Micro-structural characterization by SEM depicted that the particles tend to be more agglomerated more and more with the percentage of the reinforcement. The AFM results reveal that the surface roughness value shows a decreasing trend with SiC reinforcement while roughness increases with increase the percentage of B4C.

Machining process parameter and surface integrity in conventional EDM and cryogenic EDM of Al–SiCp MMC

Investigations were carried out on the machining of Al–MMC with 10% SiCp reinforcement, and conventional electrical discharge machining (CEDM) and a cryogenic cooled electrode in the electrical discharge machining process (CCEDM). The machining parameters included discharge current, pulse on time and gap voltage. The output responses comprised electrode wear ratio, material removal rate, surface roughness, electrode temperature, workpiece temperature, microstructure, micro hardness, SEM and EDX analysis. Discharge current, pulse on time, and gap voltage were found to have the most significant effect on electrode wear, while pulse on time with discharge current having the most significant effect on surface roughness. The electrode wear was reduced to 18% by cryogenic cooling. Surface roughness was also improved while machining with cryogenic electrode cooling. The scanning electron microscope (SEM) analysis was carried out to study the surface characteristics of the machined surface.

Structure and properties of modified compocast microsilica reinforced aluminum matrix composite

Abstract A356 aluminum alloy reinforced with 7 wt.% microsilica composites was produced by the three different processing routes viz. liquid metal stir casting followed by gravity casting, compocasting followed by squeeze casting and modified compocasting route and their properties were examined. Microstructure of liquid metal stir cast Al MMC shows agglomeration of particles leading to high porosity level in the developed material. Adopting new route of compocasting followed by squeeze casting process prevents the agglomeration sites with uniform distribution and dispersion of the dispersoids in the matrix metal. Modified compocasting process reduces the segregation of particles in the final composites thus enhancing the mechanical, tribological and corrosion properties of the composites. Superior wear-resistance properties were exhibited by the modified compocast composite compared to the unreinforced squeeze cast alloy and abrasive type wear mechanism was observed in the case of composite. Increasing the sliding speed resulted in the quick evolution of tribolayer and the wear rate of composite gets reduced. The presence of intermetallic phases like MgAl 2 O 4 , NaAlSi 3 O 8 and KAlSi 3 O 8 has a favorable effect on increased corrosion resistance of the composite. Microsilica particles significantly enhanced the compressive strength of modified compocast composites compared to the unreinforced squeeze cast Al alloy.

Fabrication of Al-TiB<SUB>2</SUB> Metal Matrix Composites for Evaluation of Surface Characterization and Machinability

The present study discusses about the fabrication of Al MMC with TiB2 as 2% reinforcement with 400 mesh particle size by novel vacuum stir casting method. A series of experiments performed to know morphology and surface topography of developed MMC. Micro structural observation along with the SEM and XRD testing has been carried out to investigate the distribution of TiB2 particle reinforced in Al2014 matrix. EDAX report has been generated of a standard specimen to know the weight percent of all the materials that were developed during the casting process. Machinability test has been carried out on medium duty lathe with coated carbide insert by using Taguchi L9 orthogonal array to know the surface roughness values with a selection of different cutting parameters as cutting speed, feed rate and cutting depth respectively for three different levels. The optimal cutting conditions were found using the Signal-to-Noise (S/N) ratio of surface roughness parameters (Ra, Rz) and material removal rate according to “the-smaller-the-better” and “larger-the-better” criteria respectively. Taguchi response analysis is used to optimize the parameters influencing the objectives. To get good surface finish high cutting speed and lower feed rates has been found as optimal parameters of developed Al-TiB2 MMC. Keywords: Aerospace Application, MMC, Taguchi Analysis, Tib2 Particle, Vacuum Stir Casting

Frictional Heating During Sliding of two Semi-Spaces with Arbitrary Thermal Nonlinearity

Abstract Analytical and numerical solution for transient thermal problems of friction were presented for semi limited bodies made from thermosensitive materials in which coefficient of thermal conductivity and specific heat arbitrarily depend on the temperature (materials with arbitrary non-linearity). With the constant power of friction assumption and imperfect thermal contact linearization of nonlinear problems formulated initial-boundary thermal conductivity, using Kirchhoff transformation is partial. In order to complete linearization, method of successive approximations was used. On the basis of obtained solutions a numerical analysis of two friction systems in which one element is constant (cermet FMC-845) and another is variable (grey iron ChNMKh or aluminum-based composite alloy AL MMC) was conducted

Effects of humidity and corrosion on the tribological behaviour of the brake disc materials

The aim of the present work was to investigate the influence of humidity and corrosion in a high-salinity environment on the friction and wear behaviour of three brake disc materials. Experiments were conducted using a commercially built disc-on-pin machine (SRV4, Optimal Instruments, Germany). Three different disc brake materials were used: cast iron (type FG25), chromium bearing steel (type 100Cr6) and an aluminium-based composite Al MMC (type A359/SiCp). The pin in all tests was a commercial automotive brake pad material. The results showed that the friction coefficients and the wear rate for all tested materials were sensitive to increasing normal load and the sliding speed. At increased humidity level, a water film formed and behaved as a lubricant. The corrosion due to salt spray had a larger influence on the tribological behaviour of the cast iron and the chromium steel than it did on the Al MMC. The Al MMC A359/SiCp exhibited a better tribological behaviour than the other brake disc materials used in this investigation under the given test conditions.

Optimization of Tensile Characteristics of Al 356 alloy reinforced with volume fraction of Red Mud Metal Matrix Composite

In order to achieve optimum values for tensile characteristics such as high strength, yield strength and percentage of elongation the artificial ageing treatment were applied. The red mud collected from MALCO, Mettur,TamilNadu, India, is preheated in the furnace up to 500o C and 53 micron sized particles are mixed with Al356alloy. Al MMC specimens are manufactured by stir casting technique using Al356 alloy reinforced with different volume percentage (5%,10%, 15% and 20%) of red mud. The standard artificial ageing treatment for Al 356 alloy followed heat treatment and solution treatment for different temperature at varied time and temperature are carried out. The effect of solution treatment and artificial aging on the microstructure and tensile properties were studied by scanning electron microscopy and by carryout tensile test in the universal testing machine by applying constant load for all different volume percentage of red mud. The experimental results are optimized by using taguchi orthogonal array design method using Qulitek software, the experiments were conducted on three parameters with four levels, the three parameters are volume fraction, temperature and aging time. The influences of the various parameters are discussed, the validation of experiments is done by analysis of variance techniques the result shows that the ultimate strength can be obtained for 180–200°C and 4-6hrs of 20% of volume fraction, The experimental results also show with the increase in time and temperature the ultimate strength also increases, the yield strength also found to be increases with the increase in temperature and time but the yield strength increase and decreases with the increase percentage of elongation. The percentage of elongation increases with the increase in temperature.

Tribological Characteristics of Al 356 Alloy Reinforced with Red Mud

Recent attention is focused on issues of utilization of industrial wastes. The paper deals with the Tribological characteristics of Al356 alloy reinforced with red mud of different volume fractions. Red mud is a gangue produced during the extraction of alumina, disposal of which has become a major issue. In recent years, the utilization of red mud as a filler material has increased due to its chemical composition, which includes metals like Fe2O3, Al2O3, Na2O and TiO2, etc. These metals exhibit good wear characteristics. The red mud collected from Malco, TamilNadu, India, is preheated in the furnace up to 500o C and 53 micron sized particles are mixed with Al356 alloy. Al MMC disc is manufactured by stir casting technique using Al356 alloy reinforced with different volume percentage (5%, 10%, 15% and 20%) of red mud. Pins of 10 mm diameter are machined from the brake shoe liner of commercial passenger car. The wear tests are then carried out on a pin-on-disc machine.. Wear rate is calculated for different percentage of reinforcement under different test conditions. The wear grooves formed on the Al MMC disc for all percentage of red mud are analyzed using optical micrograph. The results show that applied load and sliding velocity have significant influence on wear rate of composite. The co-efficient of friction decreases when the load increases. Experimental analysis is carried using Taguchis Design of Experiment method with various parameters like sliding velocities, applied load and composite volume fraction to identify the key factors that influence the wear rate. The Taguchi experiments results confirm the actual results obtained from the numerical calculation.

Synthesis of nanodiamond-reinforced aluminum metal composite powders and coatings using high-energy ball milling and cold spray

Nanodiamond-reinforced aluminum metal matrix composites (ND–Al MMC) powders were synthesized by means of high energy ball milling. We present a systematic study of the effect of various milling conditions on the structure and properties of the resulting MMC powders. The described method can be used to control important powder characteristics, including particle size and shape, Al crystal size and residual strain, and structural integrity and dispersion of the nanoparticle inclusions, a crucial requirement for subsequent powder consolidation. Raman spectroscopy was utilized for the first time to directly verify the structural integrity and the dispersion of ND in the Al matrix. For low ball-to-powder ratios (BPR), average particle size and size range of the ND–Al composite powders were found to decrease during milling, while the hardness increases. A BPR of 10:1, a milling time of 10h, and a ND content of 10wt.% were most effective in obtaining small powder particle sizes, small Al crystal sizes, and improved mechanical properties reaching a hardness of 3.46GPa, a 210% increase over the pristine, untreated Al powder (1.10GPa). Finally, we demonstrate that the as-produced composite powders are well-suited for low-temperature consolidation processing by fabricating the first cold-sprayed ND–Al MMC coating.

Three-dimensional FE model for calculation of temperature of a thermosensitive disc

An effect of variations of the temperature-dependent thermophysical properties of materials of a pad and a disc on the temperature generated due to friction was studied. A three-dimensional boundary-value problem of heat conduction of the disc heated locally within the contact area by the moving with the constant deceleration heat flux and the intensity proportional to the specific capacity of friction was formulated. An issue was solved numerically using the finite element method (FEM). The experimental dependences curves of the thermal conductivity and the thermal diffusivity on the temperature ranging from 20 to 500 °C indispensable for the calculations were approximated using Chichinadze's methodology. The comparative analysis of temperature values on the contact surface of the disc obtained with and without influence of temperature dependence of the four different pad and the same quantity of the disc materials was carried out. It was demonstrated that apparent temperature differences arose for each friction couple combining temperature-dependent and constant properties of materials, however, the largest observed discrepancy (13.7%) occurred for the disc made of aluminium alloy series Al MMC. Other disc materials i.e. iron alloy series FCD50, cast iron ChNMKh and steel EI-696 revealed relatively equal temperature differences of order of 6.4%. Furthermore incorporated in the formula for the heat partition temperature variability of the thermophysical properties of materials affected the resulting contact temperature of the disc for friction couple combined exclusively with the titanium pad VT-14 (3.1%).

트라이볼로지 관점에서 철도차량의 경량 제동 디스크와 라이닝의 특성 평가

*Graduate School of Railroad, Seoul National University of Technology*Korea Railroad Research Institute(Received February 2, 2011; Revised March 12, 2011; Accepted March 13, 2011)Abstract − The brake disc materials for railway vehicle have been mainly used cast-iron. The brake disc and padshould be light, resist to a thermal crack and absorb enough friction energy. In order to satisfy this requirement,aluminum alloy brake disc for railway vehicle has been newly developed. The aluminum itself has not been con-sidered the friction material for railway vehicle. However, in the case of aluminum composite with dispersedceramic particles, friction characteristics, resistance to wear and heat are much improved. In the present study,aluminum composite brake disc of 20% ceramic particle and three kinds of organic pads have been tested indynamometer. The results show that Al MMC brake disc and pad have good friction coefficient and wear rate,and thermal cracks in brake disc have not been initiated. Also, the Al MMC brake disc can be applied to railwayvehicle of 150 km/h.Keywords − brake disc(제동디스크), brake lining(제동라이닝), friction coefficient(마찰계수), wear rate(마모량), Al brake disc(알루미늄 제동디스크), light weight(경량화)

Corrosion protection and formation mechanism of anodic coating on SiC p/Al metal matrix composite

The corrosion protection from sulfuric acid anodized coatings on 2024 aluminum and SiC particle reinforced 2024 aluminum metal matrix composite (SiC p/2024Al MMC) in 3.5 wt.% NaCl aqueous solution was investigated using electrochemical methods. The results show that the anodized coating on 2024Al provides good corrosion protection to 3.5 wt.% NaCl, and the anodized coating on the SiC p/2024Al MMC provides some corrosion protection, but it is not as effective as for 2024Al because non-uniformity in thickness and cavities present are associated with the SiC particulates. Cavities above SiC particles are the reason that the anodized coating on the MMC cannot be completely sealed by hot water as with anodic Al alloy. SiC particle anodizes at a significantly reduced rate compared with the adjacent Al matrix. This gives rise to alumina film encroachment beneath the particle and occlusion of the partly anodized particle in the coating. It was found that the barrier layer of anodized Al MMC is not continuous, and it is composed primarily of the barrier layer of anodized Al matrix and a barrier-type SiO 2 film on occluded SiC particles in the coating. A new formation mechanism of coating growth during anodizing of a SiC p/2024Al MMC was proposed.

Laser and lathe thread cutting of aluminium metal matrix composite

Aluminium metal matrix composites (Al MMC) with silicon carbide (SiC) particle reinforcement are promising materials due to their characteristics, such as lightweight and high wear resistance. However, their diffusion is limited by difficulties arising both in obtaining semi-finished parts and in finishing operations such as drilling and thread cutting. This paper is aimed at comparing two alternatives in thread cutting of Al MMC reinforced by SiC, the first being traditional lathe thread cutting, the other the emerging laser ablation process. The initial workpiece is a tensile test specimen obtained by investment casting process, whereas the composite was obtained mixing molten aluminium with 20% of SiC particles using the double stir method. Benefits and difficulties of using the indicated production technologies to obtain threads are presented.

Thermophysical Properties of Automotive Metallic Brake Disk Materials

The temperature distribution, the thermal deformation, and the thermal stress of automotive brake disks have quite close relations with car safety; therefore, much research in this field has been performed. However, successful and satisfactory results have not been obtained because the temperature-dependent thermophysical properties of brake disk materials are not sufficiently known. In this study, the thermophysical properties (thermal diffusivity, the specific heat, and the coefficient of thermal expansion) of three kinds of iron alloy series brake disk materials, FC250, FC170, and FCD50, and two kinds of aluminum alloy series brake disk materials, Al MMC and A356, were measured in the temperature range from room temperature to 500 °C, and the thermal conductivity was calculated using the measured thermal diffusivity, specific heat capacity, and density. As expected, the results show that the two series have significant differences in respect of the thermophysical properties, and to reduce the thermal deformation of the brake disk, the aluminum alloys with a high thermal conductivity and the iron alloys with low thermal expansion are recommended.