Alloy Based Metal Matrix Composites Research Articles

Castable composites and their application in automobiles

Aluminium alloy based metal matrix composites (MMCs) have attracted attention in the automobile sector owing to ease of manufacturing, high specific strength properties, and better wear resistance. The stir casting or liquid metallurgy technique is the most economic and direct route for producing near-net-shape MMC components. In the present investigation, an Al-4.5%Cu alloy MMC with fly ash particles has been cast by the stir casting technique. Properties such as density, hardness, wear, and tensile and compression strength of the MMC have been evaluated. Further, to test the applicability of this composite as a bearing, a bush was prepared from the composite and tested under lubricated conditions for 200 h. The bush made from the composite showed more resistance to wear than the base alloy. A cylinder liner was cast from the composite and then tested in a two-stroke petrol engine. No seizure was observed even after 400 h of testing.

Prediction of wear coefficient of Al6061–TiO 2 composites

In recent years, aluminum alloy based metal matrix composites (MMC) are gaining wide spread acceptance in several interesting applications such as piston, connecting rod, microwave filters, vibrator component, contactors, impellers and space structures. These composites possess excellent wear resistance in addition to other superior mechanical properties such as strength, modulus and hardness when compared with conventional alloys. Of all the aluminum alloys, 6061 is quite popular choice as a matrix material to prepare MMCs owing to its better formability characteristics and option of modification of the strength of composites by adopting optimal heat treatment. From the literature, it is quite evident that the focus has been centered on processing of MMCs and characterization of mechanical properties of MMCs. Tribological characteristics of several MMC systems involving glass, flyash, SiC, Al 2O 3 as discontinuous dispersoids have been reported. However, meagre data are available as regards the theoretical prediction of wear rate of MMCs. Prediction of wear rate gains impetus in present industrial scenario to assess the life of sliding components in advance to avoid huge economic losses that incur due to wear. In the light of the above, the present investigation deals with preparation of Al6061–TiO 2 composites by liquid metallurgy route. The extent of incorporation of TiO 2 in the composite was varied from 2 to 10 wt%. Microstructure studies, hardness and wear test were conducted on the cast Al6061–TiO 2 composites. Pin on disc machine was used to assess the wear resistance of the prepared composites. Load was varied from 10 to 40 N while the sliding distance was from 90 to 540 m. Wear coefficients were evaluated by using Archard's and Yang's theoretical models. Increased contents of TiO 2 resulted in higher hardness and lower wear coefficient of the composites under identical test conditions. The wear coefficient of all the Al6061–TiO 2 composites studied decreased at higher loads and larger sliding distances. The predicted values of the wear coefficient are in close agreement with the experimental ones.

Room and high temperature tensile tests on the AA6061/10vol.%Al2O3p and AA7005/20vol.%Al2O3p composites

AbstractAluminium alloy based Metal Matrix Composites (MMCs), reinforced with ceramic particles such as Al2O3 or SiC, have a number of advantages over conventional aluminium alloys, primarily enhanced stiffness and increased wear resistance. In order to improve the fields of application, fundamental understanding of the relationship between microstructural features and mechanical properties is however required. In this work, the tensile behaviour of two composites based on 6061 and 7005 aluminium alloys, reinforced with Al2O3 particles, at room temperature, at 100°C and at 150°C was studied. The ductility of the composites was found to be much lower than that of the unreinforced alloys, while a significative increase of the elastic modulus and tensile strength was found. Both materials showed a slight decrease of the tensile strength with temperature, while elongation increased. Large particles and clusters of the reinforcement were found to be locations prone to failure in the composite, due to the high stress concentrations, mainly at room temperature. With increasing temperature, the fracture surfaces showed a dimpled appearance with a large amount of plastic deformation of the matrix, indicating that void nucleation, growth and coalescence is the main fracture mechanism.

Production of aluminium alloy based metal matrix composites by a press-and sinter route

Production of aluminium alloy based metal matrix composites by a press-and sinter route

Thixoforming of a novel layered metal matrix composite

Thixoforming is a semisolid processing route capable of producing near net shape components with low levels of porosity in a single, rapid operation. It has potential for the processing of aluminium alloy based metal matrix composites (MMCs). In contrast with casting of fully liquid metal, the flow of material into the die in thixoforming is primarily laminar. Thus, a novel layered MMC structure, generated by spray forming, consisting of alternate lamellae of reinforced and unreinforced alloy, might be preserved in thixoforming. The laminated structure is intended to give an increase in toughness, compared to a homogeneously reinforced material. The material was produced by spray forming alternate layers of aluminium matrix alloy 2014 (Al–4Cu–0·8Si–0·8Mn–0·5Mg) and matrix alloy reinforced with ∼17 vol.%SiC particles. Following thixoforming, the layered structure was well preserved with good retention of layer integrity and arrangement. Impact measurements for estimating toughness (Charpy and Izod) showed limited improvement with the layered materials, relative to homogeneously reinforced ones. However, in slow crack growth (Tattersall–Tappin tests), toughness was nearly doubled when estimated in terms of an average energy of fracture from the area below the load–crosshead displacement curve. This was attributed to the reduction in the energy of the propagating crack at low strain rates, which led to a greater potential for the structure, and in particular for the unreinforced layer, to stop or slow the crack. Additionally, these layered MMC materials have provided a striking record of the die filling behaviour for metallic materials during thixoforming. The flow pattern is akin to that in conventional hot forging. This may assist in the establishment of design rules for thixoforming dies.

Superplasticity in ceramic and metal matrix composites and the role of grain size, segregation, interfaces, and second phase morphology

Abstract Structural ceramics and ceramic composites have been shown to exhibit superplasticity in recent times and this discovery has attracted tremendous interest. Although the number of ceramics that have been found to exhibit superplasticity is now quite large, there are considerable gaps in the understanding of the detailed requirements for superplasticity in ceramics. Additionally, superplastic behavior at very high strain rates (1 s−1) in metallic-based materials is an area of increasing research. In this case, the phenomenon has been observed quite extensively in aluminum alloy-based metal matrix composites and mechanically alloyed aluminum- and nickel-based materials. Again, the details of the structural requirements of this phenomenon are not yet understood. In the present paper, experimental results on superplasticity in ceramic-based materials and on high strain rate behavior in metallic-based materials are presented. The roles of grain size, grain boundary and interface chemistry, and second phase morphology and compatibility with the matrix material will be emphasized.

Effect of Alumina Fibre Content on Properties of PM 6061 Aluminium Alloy Based Composite Materials

Composite PM 6061 aluminium alloy based metal matrix composites were manufactured by wet blending of 6061 alloy powder and δ alumina Saffil fibres followed by hot direct extrusion of the powder-fibre blends in closed containers through a streamline die, then heat treated to T6 condition (solution treated at 540°C for 5 h and age hardened at 160°C for 16 h). Density depended on the reinforcement content: relative densities of 97.5% for composite material containing 30 vol.-% fibres to 99.3% for composite material with 10 vol.-% fibres were obtained

The effect of TiB 2 reinforcement on the mechanical properties of an AlCuLi alloy-based metal-matrix composite

Weldalite 049, an Al-base Cu-Li-Mg-Ag-Zr alloy, achieves 700 MPa tensile strengths in the near-peak-aged temper in virtue of the nucleation of a T(1)-type platelike strengthening precipitate. Attention is presently given to the possibility that the alloy's modulus could be further increased through the addition of high-modulus TiB2 particles, using the 'XD' process, due to TiB2's good wettability with liquid Al. An 8-percent modulus increase is obtained with 4 vol pct TiB2.