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 coefficient s of thermal expansion, tailored to approach those of steel ( similar or equal to 13 x 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. Typica l applications include aerospace components, electronic packaging, hig h precision instrumentation, and automobile engine components. The nat ure, size and the relative quantities of the different reinforcing pha ses were considered in calculations involving the optimization of the main characteristics of the composites. Fine dispersed ponders of Si3N 4, AlN, TIB2, B4C(5-20 mu m) and 3Al(2)O(3) . 2SiO(2)(20-75 mu m) were used as the strengthening phases, while pure Al, 6061 and Al-27Si-6Ni alloys were used as the matrix. The dimensional and relaxation stabil ity was investigated for several of the extruded composites. The mecha nical properties of the extruded composites and the VPS produced compo sites were tested. Through a combination of plastic deformation and he at treatment (annealing or quenching with ageing) major improvements i n the mechanical properties of the VPS composites were obtained. Varyi ng levels of improvement were seen in the ductility of the VPS composi te 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. (C) 1998 Elsevie r Science S.A. All rights reserved.