Insight into solidification microstructure control by trace TiCN–TiB2 particles for yielding fine-tuned nanoprecipitates in a hypoeutectic Al–Si–Mg alloy

Abstract

Solution heat treatment (SHT), immediately followed by water quenching, can significantly improve the strength of precipitation-hardenable metallic materials, but frequently compromises the well-defined dimensional design of the geometrically complex or thin-wall engineering components. Here, to avoid this catastrophic high-temperature scheme, we introduce an alternative conceptual strategy to design a novel hypoeutectic Al–10Si–Mg alloy especially for “as-cast” services, i.e., extraordinarily high Mg addition and trace co-incorporation of innovative in situ TiCN–TiB2 particles coupled with a direct post-solidification isothermal low-temperature stabilization treatment (LTST). The performance was carefully characterized by multi-scale characterization techniques. Solidification kinetics and the resultant microstructural arrangement response to the TiCN–TiB2 particle additions were systematically investigated. Results demonstrated that both α-Al dendrites and eutectic Si structures were substantially refined by the TiCN–TiB2 particles. In the absence of conventional SHT, the precipitation kinetics associated with the customized LTST was also thoroughly studied. Interestingly, an extremely fine dispersion and high number density of perfectly coherent GP zones and pre-β'' nanoprecipitates were found coexisting after LTST. As a result, well-combined strength and ductility were therefore achieved by the synergistic effects of trace TiCN–TiB2 particles and LTST in this Al–10Si-2.0 Mg system.