The fracture toughness and behaviour of COMRAL-85TM, a 6061 aluminium-magnesium-silicon alloy reinforced with 20 vol% Al2O3-based polycrystalline ceramic microspheres, and manufactured by a liquid metallurgy route, have been investigated. Fracture toughness tests were performed using short rod and short bar (chevron-notch) specimens machined from extruded 19 mm diameter rod, heat treated to the T6 condition. The fracture toughness in the R-L orientation was found to be lower than in the C-R or L-R orientations owing to the presence of particle-free bands in the extrusion direction. Short rod tests were also conducted for the R-L orientation on six powder metallurgy composites with particle volume fractions ranging between 5% and 30%. It was found that the fracture toughness decreased progressively with particle volume fraction, but at a decreasing rate. A detailed examination of the fracture behaviour was made for both the liquid metallurgy and powder metallurgy processed composites. �� 2008 Elsevier Ltd. All rights reserved.