Effect of Er addition on microstructural and mechanical properties of Al-11%Mg2Si alloy

Abstract

During the solidification of Al-Mg2Si alloy, the eutectic Mg2Si phase with large size and flake-like morphology forms in the structure of the alloy which results in deterioration of mechanical properties; hence, modification/refinement of eutectic Mg2Si phase using alloying elements is a prime concern. Since there is a need to investigate further the characteristics of Al-Mg2Si alloy treated by rare earth additions, this study aims to investigate the influence of different Er concentrations (0.0, 0.1, 0.3, 0.5, and 1.0 wt%) on microstructure and mechanical characteristics of hypoeutectic Al-11Mg2Si metal matrix composite. The composite materials were prepared using an in-situ casting procedure with high purity of the elements. Microstructure characterisation was carried out by optical microscopy, in which an image analyser measured the eutectic Mg2Si cell sizes. The mechanical properties of the fabricated composites were analysed using tensile and hardness tests. The findings demonstrated that the morphology of primary Mg2Si changed with 0.1 wt% Er addition from irregular or dendritic shape to a polyhedral shape and becams uniformly distributed. Microstructural observations also showed that in the Al-11Mg2Si phase, the structure of the eutectic Mg2Si phase was altered from a flake-like structure to a fibrous structure, and the size of the black embedded structures decreased from 188.7 µm in the base alloy to 168.9 µm in the alloy added with 0.1 wt% Er. Further studies on mechanical properties found that 0.1 wt% of Er addition was optimum for enhancing the hardness, UTS, and elongation values, in which the harness value increased from 67.9 to 77Hv, UTS increased from 126 to 131 MPa and elongation (%) from 1.53 to 1.60. The SEM micrographs of the composite fracture surface depicted that with the addition of Er, the brittle fracture mode changed to the ductile mode with fine dimples.