Effect of RE elements on the microstructural and mechanical properties of as-cast and age hardening processed Mg–4Al–2Sn alloy

Abstract

In the present article, the effect of Rare Earth elements on the microstructural development and mechanical properties of as cast and age treated Mg–4Al–2Sn (AT42) alloy is studied. Investigation has been conducted by optical and scanning electron microscope, XRD and tensile tests. Analysis of the data showed that alloy's dendrites turn into larger dendritic structure with sharp and narrow arms from equiaxed rosette type by addition of RE elements. In contrast to the base alloy, aging treatment shows a positive effect on the mechanical properties (yield strength, tensile strength and elongation) of AT42 + 1RE alloy mainly because of retention of the thermally stable RE containing intermetallics as strong barriers to grain growth. Also, increase of solute aluminum due to the decomposition of Mg₁₇Al₁₂ along with saturated RE elements led to formation of blocky shape Al₂RE in the microstructure during aging which enhanced the mechanical properties. It was found that the best result (yield of 70 MPa, tensile strength of 168 MPa and elongation of 14%) could be achieved by aging the AT42 + 1RE alloy at 443 K (170 °C) for 8 h. However, mechanical properties of AT42 + 1RE alloy starts to decrease after exceeding its optimum aging conditions due to the coarsening of intermetallics.