The effects of processing parameters on mechanical properties of SiCw/2124Al composites

Abstract

The aluminium alloy matrix composites with discontinuous ceramic reinforcements are regarded as potential materials for high-performance structural parts in aerospace and automobile industries. The processing parameters related with complicated fabrication process of metal matrix composite need to be strictly controlled to produce composites with reproducible and uniform mechanical properties for industrial application. The understanding of the relationships among processing parameters - microstructures - mechanical properties is very important to produce reliable metal matrix composites. In this paper the effects of processing parameters, i.e., volume fraction of whiskers, vacuum hot pressing temperature, vacuum hot pressing pressure, extrusion temperature and extrusion ratio, on mechanical properties of SiCw/2124Al composites fabricated by powder metallurgy process were investigated using a statistical technique known as Taguchi method. The vacuum hot pressing temperature was found to be the most sensitive parameter to the tensile strength. As the vacuum hot pressing temperature increased up to 570°C, the tensile strength increased due to the enhanced densification of composite and increased aspect ratio of SiC whiskers, which were resulted from the reduced strength and increased amount of liquid phase in matrix with increasing vacuum hot pressing temperature. The optimum vacuum hot pressing pressure was considered to be 70MPa, below which the remaining voids reduced the tensile strength of SiCw/2124Al composite. The tensile strength increased with increasing volume fraction of SiC whiskers. However, the volume fraction of whiskers more than 20% was not helpful to increase the tensile strength since the whiskers tend to be non-uniformly distributed. The extrusion temperature need to be higher than the solidus temperature of 2124Al matrix to reduce the damage of whiskers and to improve the alignment of whiskers. The extrusion ratio of 15:1 resulted in the highest tensile strength. The alignment of whiskers improved with increasing extrusion ratio, while the aspect ratio of whiskers decreased due to the damage of whiskers.