Influence of thermal rate treatment and low temperature pouring on microstructure and tensile properties of AlSi7Mg alloy

The combination of thermal rate treatment and low temperature pouring was proposed in the present work, and the effects of the novel melt thermal treatment on microstructure and tensile properties of AlSi7Mg alloy have been investigated. The grain size and microstructure of AlSi7Mg alloy were examined by optical microscopy (OM) and scanning electron microscopy (SEM). It was found that the grain size obviously reduced and the growth of the columnar dendrites changed into equiaxed ones by low temperature pouring, especially the novel melt thermal treatment, by which a maximum microstructure refining effect could be obtained. The refinement can be attributed to the multiplication of the nuclei in the melt. Furthermore, the morphology of eutectic silicon changed little, but the size of silicon phase was finer due to the refinement of the grain size and higher cooling rate. Because of the refinement of the grain size and eutectic silicon, the tensile properties were improved, and the ultimate tensile strength and elongation increased by 11.7% and 35.3%, respectively.

Research highlights
► The novel melt thermal treatment refines the grain size of the alloy.
► The novel melt thermal treatment makes a transition of columnar dendrites to equiaxed ones.
► The tensile properties were improved due to the refinement.