Process optimisation and numerical modelling of powder metallurgical aluminium matrix composites

摘要

The present research focuses on optimisation of a novel application of the cold uniaxial pressing and liquid phase sintering powder metallurgical method to the processing of ceramic particulate reinforced aluminium matrix composites and the numerical modelling of these advanced materials. The investigated process areas include material selection, powder mixing and powder heat treatment, lubrication type, quantity and method, compaction and ejection, green sample conditioning, sintering time, temperature and atmosphere, and sintered compact heat treatment. The methods of analysis used include particle size, shape and H20 content analysis, powder compressibility testing, ejection stress analysis, green strength testing, green compact and sintered material density measurement, macrohardness, compression and tensile testing, and both optical and scanning electron microscopy. The present numerical modelling work involves the development and use of a new geometrically versatile continuum mechanics based finite element analysis model capable of allowing the isolation of particulate volume fraction, size, and distribution variations and simulating the constitutive response of a specific composite material.ududThe process investigations have elucidated many of the factors affecting the mechanical properties of the final material and have found that small to medium sized net shape and near net shape aluminium matrix composite components may be produced by this conventional powder metallurgical processing method. It has been identified that the success of this process is strongly dependent on factors including aluminium powder and reinforcement particle size, powder heat treatment and component sintering conditions. Also, the present numerical model provides a method of predicting the response of these composite materials to thermal and mechanical loading, and allows for independent adjustment of the constitutive material properties and geometric model form to aid in the design of these versatile composites. The modelling investigations carried out indicate that internal stress development within a discontinuously reinforced metal matrix composite depends primarily on the proximity of particles, the relative orientation of particles in close proximity and the directionality of loading.