DEVELOPMENT OF PRECIPITATION HARDENED. 7075-AI/Cr7C3 COMPOSITES

Abstract

7xxx Aluminium alloys have been the centre of attraction for many researchers due to their excellent properties in the available aluminium alloys. Although, wrought and cast product of this particular alloy is satisfying most of the needs of Aerospace industry, still a need for the material with better strength to weight ratio is needed. Powder Metallurgy route is the promising one to fulfill above requirements. In this work Al 7075/Cr7C3 composite has been developed with the help of powder metallurgy route. The Al 7075 alloy was produced from elemental blend containing 5.6% Zn, 2.5% Mg, 1.6% Cu and remaining aluminium. Different compaction pressures for the optimizing after sintered properties of the matrix were investigated and analyzed with the help of green density, sintered density, densification parameter and hardness measurement. After getting optimum pressure conditions nine samples of same composition at optimum pressure were compacted and sintered at 620°C in N2 atmosphere. The sintered compacts were aged to get the peak aging time and peak hardness. An optimized amount of reinforcement was added to the matrix and sintered to form a sintered composite. This sintered composite was aged for 18-26 hours at 120°C. It was observed that presence of the hard phase not only reduced the green density but also the driving force for sintering due to restricted path for the diffusion of matter. Peak hardness during aging was found to increase and aging kinetics was accelerated in the presence of the reinforcement.