Mechanical alloying for the effective dispersion of sub-micron SiC p reinforcements in Al–Li alloy composite

Abstract

Whilst sufficient incentives such as high specific mechanical properties and ease of processing exist for particulate reinforcements for metal matrix composites, optimal processing of these particulate reinforcements is hindered by the difficulty in obtaining a finely and evenly dispersed sub-micron reinforcement. Whilst it is commonly known that finer sized (<2 μm) reinforcements produce higher specific mechanical properties, they also encounter significant agglomeration problems at that size range, resulting in poor dispersion and subsequently less than optimal mechanical properties for the composite produced. One recent approach attempted in resolving agglomeration problem is the use of a Mechanical Alloying (MA) method. This paper reports on the use of a mechanical alloying (MA) method to disperse SiC particles with an average particle size of 0.8 μm in an Al–Li alloy matrix medium, followed by a high deformation process to fully consolidate the composite. The resulting composite mix was then compacted using a Cold Isostatic Press followed by a high deformation consolidation using hot extrusion. By using a homogeneity index ( Q) to quantify the dispersion, and subjecting the resulting consolidated composite to various mechanical tests, the effect of the Q value on the resulting mechanical properties has been established, indicating that a low Q value (implying a good reinforcement dispersion) resulted in optimal mechanical properties. The lowest Q values were obtained with 8 h of milling at 200 rpm. The resulting MMC showed improved tensile modulus and strength, but as in larger sized reinforcements, the elongation values obtained were low.