Microstructure and tensile properties of graded Al–Mg2 Si in situ composites fabricated by centrifugal casting

Abstract

Al–Mg2 Si in situ composite tubes were fabricated by a centrifugal casting process. The microstructure and tensile strength of the composite tubes were examined revealing an inhomogeneous distribution of Mg2 Si particles along the radial direction. Adjacent to the rapidly cooled area, near the outer periphery, in situ particles were forced inwards leaving behind a particle free region in the middle part of the tubes. Increasing Mg2 Si weight percentage in the aluminium matrix induced dendrite formation in the rapidly cooled area and the width of the particle free region in the middle part of the cylinder wall decreased. The particle distribution gradient in the inner region also decreased with increasing Mg2 Si content. The width of the particle free region and the particle distribution gradient were both influenced by the gradually varying viscosity of the liquid alloy as it solidified. The tensile strength of the centrifugally cast tubes increased from inner to outer periphery. High volume fractions of Mg2 Si particles of between 50 and 70 vol.-% reduced the strength of the composites.