Secondary aluminium alloys are limited in their use for structural automotive applications due to their high Fe contents, which frequently result in the formation of brittle Fe-rich intermetallic phases that are detrimental to the ductility of aluminium castings. Recently, a new secondary Al-Si-Mg alloy with high Fe content (~0.44 wt.%) suitable for structural die casting applications was developed with controlled additions of Mn and Sr based on CALPHAD modelling and experimental validation [1,2]. Structural die castings produced by vacuum die casting are rarely used in as-cast condition and are usually subjected to additional heat treatment to optimize the mechanical properties for a specific application. As a result, it is critical to investigate the heat treatment response of the new secondary alloy, which has higher Cu and Zn contents in addition to a higher Fe level than its primary counterparts, such as EZCast from Alcoa, Silafont36 from Rheinfelden Alloys, and Aural 2 from Rio Tinto.

In this study, the heat treatment response of the recycled Al-Si-Mg alloy produced by vacuum die casting process is investigated experimentally and computationally to evaluate the effect of increased contents of Fe, Cu, and Zn on the final mechanical properties and microstructure. An integrated precipitation and strengthening model based on the Kampmann-Wagner numerical (KWN) framework is used to investigate the effect of impurity content on nucleation, growth, and coarsening mechanisms of precipitating phases. The precipitation model is fully coupled with PanEngine, a multi-component thermodynamic calculation software from CompuTherm LLC (Madison, WI), and capable of handling co-precipitation of multiple meta-stable phases with different morphologies. The computational investigation of the precipitation process is supported with detailed microstructural characterization [3,4].

References

[1] E. Cinkilic, C.D. Ridgeway, X. Yan, A. A. Luo, Metallurgical and Materials Transactions A, 2019, 50, 5945-5956.

[2] E. Cinkilic, M.P. Moodispaw, J. Zhang, J. Miao, A. A. Luo, Metallurgical and Materials Transactions A, 2022, 53, 2861-2873.

[3] E. Cinkilic, X. Yan, A.A. Luo, Metals, 2020, 10, 1356-1370.

[4] J. Miao, C. Zhang, A.D. Klarner, J. Zhang, E. Cinkilic, F. Zhang, A.A. Luo, Materialia, 2022, 21, 101348