Investigation on Reinforcement Incorporation Factor and Microstructure of Al 7075/Submicron-TiB2 Metal Matrix Composites Processed through a Modified Liquid Metallurgy Technique

Abstract

In this paper 0.8, 1.2, 1.6 and 2 wt.% of submicron-TiB2 particulate reinforced Al 7075 metal matrix composites (MMCs) were fabricated following a modified liquid metallurgy technique, which included ball milling, semi-solid stirring and ultrasonic agitation assisted squeeze casting method. Objective was to investigate their reinforcement incorporation factors (RIFs), microstructure through optical microscopy (OM) and scanning electron microscopy (SEM), and phase identification through X-ray diffraction (XRD) analysis. Phase distribution of different elements was analyzed through energy dispersive X-ray spectroscopy (EDS), and spatial distributions of elemental constituents were verified through elemental mapping. Mechanisms of TiB2 particulate dispersion and cluster segregation were highlighted. Results revealed excellent incorporation and dispersion uniformity of the reinforcements in the matrix phase. Squeeze casting process promoted the heterogeneous nucleation rate and rapid solidification, which resulted formation of Al-Zn-Mg-Cu based compounds in the dendritic regions. Occasional formation of reaction by-products (Al4C3) was observed at the interface of 1.2 wt.% TiB2 reinforced MMC. Reduction of precipitates and large grain refinements were observed for the MMC containing 1.6 wt.% of TiB2. In the microstructure of Al 7075/2 wt.% TiB2 MMC, superior dispersion of reinforcements at grain boundaries and inter-dendritic regions, along with presence of metastable η-MgZn2 phases was identified. Crystalline phase identification of all the composite samples was also performed through XRD analysis, which validated the elemental phase distribution results of EDS.