Effect of T6, RRA and nano chromium carbide content on microstructure and mechanical properties of AA7075-Cr3C2 nanocomposite

Abstract

In the present study, AA7075 nanocomposites reinforced with varying weight percentage of Cr3C2 nano particles were successfully synthesized by stir casting technique. The pre-milled powder of Cr3C2 nano particles and aluminum powder was incorporated into molten AA7075 during stir casting for uniform dispersion of nano particles. Thereafter, the nanocomposite samples were aged at T6 and RRA (Retrogression and Reaging). The microstructural characterization examined by SEM and optical microscopy revealed uniform distribution of nano particles up to 1.5 wt.% content, above which the agglomeration occurred. The grain refinement was observed with increase in reinforcement content. The T6 and RRA aging treatment led to reduction in the amount of eutectic phases and grains were further more refined. The combined effect of reinforcement addition and aging, significantly improved the strength and hardness, but deteriorated the ductility. The hardness increased from 110.1 BHN for as cast alloy to 159.3 BHN for T6 treated 1.5 wt.% Cr3C2 nano particles reinforced nanocomposite. Similarly, the maximum value of ultimate tensile strength (308.77 MPa) and impact strength (9.3 J) were obtained for T6 treated 1.5 wt.% Cr3C2 nano particles reinforced nanocomposite. Also, T6 treated nanocomposite showed better strength and hardness whereas RRA treated nanocomposites possessed better ductility.