STRUCTURE, FRACTURE-TOUGHNESS, AND FATIGUE OF 2 ALUMINUM-MATRIX COMPOSITES PRODUCED BY VERTICAL SQUEEZE CASTING TECHNIQUE

Composite materials produced from ceramic reinforcement of aluminium a lloys have some properties that are better (higher modulus and strengt h, lower thermal expansion coefficient and density, and good creep and wear resistance) than those of the conventional monolithic aluminium alloys. However, they have a poor fracture toughness. The aim of the p resent work was to characterise the structure and mechanical propertie s of two different aluminium matrix composites (AS9C1G/20%(Al2O3-SiO2) and 2014/20%(Al2O3-SiO2)) manufactured using the vertical squeeze cas ting technique. Tensile, plane strain fracture toughness, and fatigue crack growth rate tests were carried out. In particular, the influence of specimen geometry on the toughness tests was examined. It was foun d that chevron notched short bar specimens gave roughness values simil ar to 40% higher than other types of specimens. Fatigue crack growth r ate data were interpolated using some semiempirical models. An accurat e metallographic investigation of both the structures and the fatigue fracture surfaces was carried out using optical microscopy and energy dispersive spectroscopy with SEM. (C) 1997 The Institute of Materials.