The properties and microstructure of Al-based composites reinforced with ceramic particles

Aluminum (Al)-based composite materials which were produced using both powder metallurgical and vacuum plasma spraying (VPS) techniques are presented. The objective was to produce materials with low coefficients of thermal expansion, tailored to approach those of steel (≃13×10−6 K−1), and to improve the mechanical properties of the matrix. Composite materials based on Al are used in different fields where weight and thermal stability are key requirements. Typical applications include aerospace components, electronic packaging, high precision instrumentation, and automobile engine components. The nature, size and the relative quantities of the different reinforcing phases were considered in calculations involving the optimization of the main characteristics of the composites. Fine dispersed powders of Si3N4, AlN, TiB2, B4C (5–10 μm) and 3Al2O3·2SiO2 (20–75 μm) were used as the strengthening phases, while pure Al, 6061 and Al–27Si–6Ni alloys were used as the matrix. The dimensional and relaxation stability was investigated for several of the extruded composites. The mechanical properties of the extruded composites and the VPS produced composites were tested. Through a combination of plastic deformation and heat treatment (annealing or quenching with ageing) major improvements in the mechanical properties of the VPS composites were obtained. Varying levels of improvement were seen in the ductility of the VPS composite materials (elongation values ranging from two to ten times greater than the as-sprayed values). The ultimate tensile strengths were also improved by 30–75% compared to the as-sprayed values.