A New Recycled Al-Si-Mg Alloy for Sustainable Structural Die Casting Applications

The use of secondary aluminum for structural components in the automotive industry is limited by the high Fe contents in recycled alloys which often result in the formation of brittle beta-Al5FeSi phase which reduces the ductility of aluminum castings. In this study, a new secondary Al-Si-Mg alloy with high Fe content (about 0.44 wt pct) was developed for die casting applications. Based on thermodynamic modeling, manganese was added to obtain a designed Fe-to-Mn ratio of 2 which successfully suppressed the formation of beta-Al5FeSi phase, by forming alpha-Al-15(Fe,Mn)(3)Si-2 phase with rounded or hexagonal morphology. Additionally, a fine needle-like pi-Al8FeMg3Si2 phase was also formed within the eutectic regions. The new recycled alloy showed comparable mechanical properties in the as-cast and heat-treated (T5 and T6) conditions to three major primary die cast alloys (<= 0.2 wt pct Fe) with similar composition. Ductility up to 7.4 pct from tensile elongation was achieved in the as-cast recycled alloy due to the modification and refinement of alpha-Al-15(Fe,Mn)(3)Si-2 by Mn and Sr additions. Tensile elongation was further improved to 9.1 pct after T6 treatment as a result of dissolution of pi-Al8FeMg3Si2 phase, defragmentation of alpha-Al-15(Fe,Mn)(3)Si-2, and the spheroidization of Si phase. This new alloy provides a promising path for increasing usage of recycled aluminum with high Fe content in structural die castings for automotive and other applications.

Automated summary

A new secondary Al-Si-Mg alloy with high Fe content has been developed for die casting applications. The addition of manganese successfully suppressed the formation of a brittle phase and led to improved mechanical properties. This alloy provides a promising path for increasing usage of recycled aluminum with high Fe content in automotive and other applications.