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Abstract
Al-Si-based casting alloys have a great potential in various industrial applications. Common strengthening strategies on these alloys are accompanied inevitably by sacrifice of ductility, known as strength-ductility trade-off dilemma. Here, we report a simple route by combining rapid solidification (RS) with a post-solidification heat treatment (PHT), i.e. a RS + PHT route, to break through this dilemma using a commercial Al-Si-based casting alloy (A356 alloy) as an example. It is shown that yield strength and elongation to failure of the RS + PHT processed alloy are elevated simultaneously by increasing the cooling rate upon RS, which are not influenced by subsequent T6 heat treatment. Breaking through the dilemma is attributed to the hierarchical microstructure formed by the RS + PHT route, i.e. highly dispersed nanoscale Si particles in Al dendrites and nanoscale Al particles decorated in eutectic Si. Simplicity of the RS + PHT route makes it being suitable for industrial scaling production. The strategy of engineering microstructures offers a general pathway in tailoring mechanical properties of other Al-Si-based alloys. Moreover, the remarkably enhanced ductility of A356 alloy not only permits strengthening further the material by work hardening but also enables possibly conventional solid-state forming of the material, thus extending the applications of such an alloy.
Highlights
Elongation to failure (ETF) achieved by combining the RS +PHT route with the commonly used T6 heat treatment stands beyond the region showing strength-ductility trade-off behavior (Fig. 1), disobeying the general trend of strength-ductility trade-off of the A356 alloy. This can be ascribed to the hierarchical microstructure formed by the RS +PHT route, i.e. highly dispersed nanoscale Si particles in the interior of Al dendrites and nanoscale Al particles decorated in eutectic Si
Since the formation of the hierarchical microstructure being responsible for increasing simultaneously the strength and ductility depends only on the RS +PHT route, the current strategy of engineering microstructure may offer a general pathway in tailoring mechanical properties of Al-Si-based alloys
The preliminary results show that the mechanical property of A356 alloy can be improved significantly
Summary
Elongation to failure (ETF) achieved by combining the RS +PHT route with the commonly used T6 heat treatment (solid-solution treatment +artificial aging) stands beyond the region showing strength-ductility trade-off behavior (Fig. 1), disobeying the general trend of strength-ductility trade-off of the A356 alloy. This can be ascribed to the hierarchical microstructure formed by the RS +PHT route, i.e. highly dispersed nanoscale Si particles in the interior of Al dendrites and nanoscale Al particles decorated in eutectic Si. This can be ascribed to the hierarchical microstructure formed by the RS +PHT route, i.e. highly dispersed nanoscale Si particles in the interior of Al dendrites and nanoscale Al particles decorated in eutectic Si The former enhances the work hardening of Al dendrites, while the latter leads to the ductilization of eutectic Si phase. The remarkably enhanced ductility of the RS +PHT processed A356 alloy permits further strengthening the material by work hardening as well as forming the material via. conventional solid-state forming techniques, which is expected to extend the applications of such an alloy
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