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.

SiCp/6061Al composites with volume fractions of 5%, 10%, and 15% were prepared by the vacuum hot pressing sintering. Their microstructure and fracture morphology were observed and analyzed with an optical microscope and a scanning electron microscope. The elastic–plastic behavior of the 6061Al matrix in the composites was studied by using the load–displacement curve obtained by the nanoindentation test, and the plastic constitutive equation was established. The representative volume element (RVE) model was established based on the geometric characteristics of the SiC particles identified by using image processing technology from the metallographic structure. The deformation and fracture process of the SiCp/6061Al composites under the uniaxial tensile load was simulated microscopically, and the microscopic deformation and fracture characteristics and mechanical properties of SiCp/6061Al composites under different interface strengths and different SiCp volume fractions were revealed.

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