Microstructure-property correlations in ultrasonically processed AA8011-B4C composites with enhanced mechanical, morphological, and tribological performance for lightweight aerospace and automotive applications

Abstract

The aluminium matrix composites produced by the incorporation of ceramic particulates have proven to be desirable materials for lightweight structural and tribological applications. In the present investigation, AA8011-B 4 C composites with reinforcement percentages ranging from 0-10 wt.% were prepared by an ultrasonic-assisted stir casting process, and correlations were established between the processing, microstructure, and multifunctional properties. The introduction of energy in the form of ultrasound promoted acoustic cavitation and streaming, which resulted in significantly better wettability and uniform particle dispersion at low, as well as intermediate reinforcement levels. The microstructural analysis showed that the reinforcement levels as high as 6-8 wt.% resulted in considerable grain refinement and uniform distribution of B 4 C particles; however, further increase in the reinforcement level resulted in particle agglomeration and porosity. Mechanical characterization showed significant improvement in mechanical properties such as an increase in hardness by about 95-105 % and tensile strength by 55- 60%, and compressive and flexural strength by 45-60 % respectively; however, ductility was reduced because of the limited mobility of the dislocations. Tribological tests showed that the wear rate and coefficient of friction decreased significantly, which was explained by the increase in surface hardness, load-bearing capacity, and the formation of an effective and stable tribo-layer during sliding. The dispersion of the uniform reinforcement resulted in moderate improvement in corrosion resistance, while it deteriorated at higher B 4 C content because of the presence of microstructural heterogeneities. The strengthening mechanisms that controlled the strengthening behavior were synergistic load transfer, Orowan strengthening, grain refinement, and dislocation generation attributed to thermal expansion mismatch.