Work

In-situ SEM observation and CALPHAD guiding optimization of morphology of Fe-bearing phases in solution heat treated die-cast Al-Si alloys

Year: 2026

Type: article

Abstract: Conventional T6 heat treatment of thin-wall die-cast Al-Si alloys induces blistering and distortion due to inherent porosity. Short-time solution treatment (SST) has been demonstrated to solve this problem, though determining an optimized time remains challenging. This study addresses this challenge by integrating CALPHAD (Calculation of Phase Diagrams) with in-situ SEM solution experiments to design an Al-9Si-0.4Mg-0.1Fe-(0.2~0.25)Mn (wt.%) alloy and optimize a 20-minute SST at 530°C. In this CALPHAD-designed alloy, formation of the harmful β-Al5FeSi phase was suppressed, while metastable π-Al9FeMg3Si5 phase was promoted. In-situ heating experiments revealed that π-Al9FeMg3Si5 dynamically decomposed into submicron α-Al15(Fe, Mn)3Si2 dispersoids. Subsequent aging (160°C/4 h) generated dense β″ precipitates, achieving a strength-ductility synergy with a yield strength of 275 ± 5 MPa and an elongation of 11 ± 1%. This method replaces trial-and-error approaches, providing a cost-effective route to bypass porosity constraints and advance high-performance die-cast alloys for thin-wall applications.

Source: Materials & Design

DOI: 10.1016/j.matdes.2026.115684