The production and application of metal matrix composite materials

Production and mechanical properties of Al2O3 particle-reinforced 2024 aluminium alloy composites

Aluminum alloys possess a number of mechanical and physical properties that make them attractive for automotive applications, but they exhibit extremely poor resistance to seizure and galling. Reinforcement of aluminum alloys with solid lubricants, hard ceramic particles, short fibers and whiskers results in advanced metal-matrix composites (MMC) with precise balances of mechanical, physical and tribological characteristics. Advanced manufacturing technologies such as squeeze infiltration of molten alloys into fiber performs can be employed to produce near net-shape components. Brake rotors, pistons, connecting rods and integrally cast MMC engine blocks are some of the successful applications of Al MMCs in automotive industry. This paper gives an overview of the tribological behavior of Al MMCs reinforced with hard particles, short fibers, and solid lubricants, and the technologies for producing automotive parts from these novel materials.

Aluminum Metal-Matrix Composites for Automotive Applications: Tribological Considerations

Dry sliding wear of discontinuously reinforced aluminum composites : review and discussion

The mechanism of corrosion protection of the widely used 2024-T3 aluminum alloy by cerium and lanthanum inhibitors in chloride media is described in detail in the present work. The corrosion process was investigated by means of scanning Kelvin probe force microscopy (SKPFM), in situ atomic force microscopy, and scanning electron microscopy coupled with energy dispersive spectroscopy. Employment of the high-resolution and in situ techniques results in a deep understanding of the details of the physical chemistry and mechanisms of the corrosion processes. The applicability of the SKPFM for mechanistic analysis of the effect of different corrosion inhibitors is demonstrated for the first time. The inhibitors under study show sufficient hindering of the localized corrosion processes especially in the case of pitting formation located around the intermetallic S-phase particles. The main role of Ce(3+) and La(3+) in the corrosion protection is formation of hydroxide deposits on S-phase inclusions buffering the local increase of pH, which is responsible for the acceleration of the intermetallics dealloying. The formed hydroxide precipitates can also act as a diffusion barrier hindering the corrosion processes in active zones. Cerium nitrate exhibits higher inhibition efficiency in comparison with lanthanum nitrate. The higher effect in the case of cerium is obtained due to lower solubility of the respective hydroxide. A detailed mechanism of the corrosion process and its inhibition is proposed based on thermodynamic analysis.

Mechanism of corrosion inhibition of AA2024 by rare-earth compounds.

SiC p -reinforced Al-4.5% Cu-1.5% Mg composite specimens were processed through vigorous stirring of the carbide in a semi-solid alloy slurry, remelting and casting. The specimens were examined microstructurally and their tribological properties were evaluated both in the as-cast and heat-treated conditions by pin-on-disk tribometry and automatic scratch testing. The specific wear rate and the friction coefficient between a diamond stylus and the polished specimen surface decreased, and the composite microhardness increased with increasing volume fraction carbide, and decreasing carbide particle size and spacing. A solution and ageing treatment led to an increase in wear resistance and composite microhardness, and a reduction in friction coefficient.

Tribological properties of SiCp-reinforced Al-4.5% Cu-1.5% Mg alloy composites

Aluminum–ceramic cenospheres syntactic foams produced by powder metallurgy route

SiC p -reinforced Al-4.5%Cu-1.5%Mg composite specimens were processed by vigorous stirring of the carbide in a semi-solid alloy slurry, followed by remelting and casting (stir-casting). The tensile and fatigue properties were evaluated in the as-cast and in the heat-treated conditions. In monotonic tensile testing, reinforcement with SiC p produced a substantial increase in the work hardening of the material. This increase became more significant with increasing volume fraction of carbide. The yield and ultimate tensile strength, and the elastic modulus of the material, increased with heat-treatment and volume fraction of carbide at the expense of ductility. These properties are inferior to those of other reinforced, more complex aluminum alloys processed by other methods. In stress-controlled fatigue tests under fully reversed ( R = −1) bending conditions, the fatigue life of the composite was longer than that of the unreinforced specimen at intermediate and lower stress levels. At higher stress levels the improvement was negligible. In heat-treated reinforced alloy specimens the fatigue strength at 1 × 10 7 cycles decreased with increasing carbide particle size. With solid solution and precipitation strengthening, as well as carbide dispersion strengthening of the alloy, the crack growth threshold stress intensity factor K th , increased, as did the crack initiation time and the crack growth rate.

Stefanos Skolianos

Papers

Tribological properties of SiCp-reinforced Al-4.5% Cu-1.5% Mg alloy composites

Aluminum–ceramic cenospheres syntactic foams produced by powder metallurgy route

Mechanical behavior of cast SiCp-reinforced Al-4.5%Cu-1.5%Mg alloy

Comparative examination of the microstructure and high temperature oxidation performance of NiCrBSi flame sprayed and pack cementation coatings

A study on pitting behaviour of AA2024/SiCp composites using the double cycle polarization technique.