Processing of submicron SiC reinforced Al-Li composites by mechanical milling

The processing of metal matrix composites (MMC) containing fine ceramic reinforcement (< 2 mu m) by powder metallurgy route is restrained by agglomeration of the ceramic particles. This paper reports the use of mechanical milling (MM) to circumvent some of the problems involved in production of AI-Li based MMC reinforced with submicron ceramic reinforcement. The matrix in this study is gas atomized AA 8090 grade Al-Li and the reinforcement is SiC with an average particle size of 0.8 mu m. The investigation focused on optimization of certain process parameters such as milling duration and milling speed in mechanical milling. The mechanically milled composite powders are consolidated by cold isostatic pressing (CIP), followed by hot pressing in argon atmosphere and hot extrusion. The results show that a milling time of 8 hours, and a milling speed of 200 rpm are required for uniform dispersion of SiC particles. The distribution of SiC in AI-Li is quantified using a homogeneity index, Q. Tensile testing of the specimens shows an obvious increase in Young's modulus. The composite with 15 vol% SIC possess a modulus of 104.5 GPa, and ultimate tensile strength (UTS) of 519 MPa. However, the elongation is reduced from 3.78% to 1.25%.