Innovative light metals: metal matrix composites and foamed aluminium

Low weight is required especially for those means of transport, in which material properties have to be evaluated with respect to their specific mass. The possibility of increasing the specific properties of recyclable light metals are described: reinforcements by ceramic particulates, by continuous ceramic or carbon fibres, or by the reduction of weight by foaming the metal. Examples of castings, extrusions and forgings of particulate reinforced (<30 vol.%) aluminium alloys are given and their advantages including stiffness and wear resistance are presented. The technique of selective reinforcements by co-extrusion of particulate reinforced alloys together with conventional alloys is described. High volume fractions (> 40 vol.%) of reinforcements can be produced by gas pressure infiltration of either particulate or fibre preforms. In the case of aluminium matrix, the specific strength can be increased by a factor of up to 15, and the specific stiffness by a factor of up to 7, whereas for carbon fibre reinforced magnesium the specific strength can be increased even more. The anisotropy of fibre reinforced metal matrix composites is discussed as well as the possibilities to use cross ply preforms. The technique of foaming aluminium alloys yields materials with a specific mass in the range of 0.3-1.0 g/cm(3) structures with essentially closed pores exhibit higher specific stiff ness for beams and membranes than massive metal. The measurement and definition of stiffness and strength values appropriate for aluminium foams are presented by referring to compression tests. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.