Pure Al matrix composites produced by vacuum hot pressing: tensile properties and strengthening mechanisms

Al matrix composites reinforced by spherical intermetallic particles, were consolidated from gas atomized elemental Al and Al-Cu-Fe alloy fine powders (< 10 mum) by a vacuum hot pressing technique. The composites were made from two types of powders including commercial inert gas atomized powder (99.7%) and high purity powder (99.99%) produced by a gas atomization reaction synthesis technique. The microstructures and tensile properties of the composites with three different volume fractions of the reinforcement particles (15, 20 and 30 vol.%) were characterized. Microstructural analysis of the samples demonstrated that the quasicrystalline phase in the Al-Cu-Fe particles transformed to a crystalline omega phase, which has similar elastic modulus, CTE, and hardness properties, but a reduced density. All the composites appear to be fully dense, with strong interparticle bonding, and exhibit elastic modulus values approaching upper bound predictions by rule of mixtures. Tensile test results and neutron diffraction measurements allowed an assessment of the relative influence of direct and secondary composite strengthening mechanisms on the yield strength of this model composite system. The results suggest that for elemental Al matrix composite samples without precipitation strengthening and severe strain hardening during consolidation, the direct and relevant secondary strengthening mechanisms can be combined to predict accurately the yield strength increase of the composites. (C) 2004 Elsevier B.V. All rights reserved.