Understanding crystal structure and morphology evolution of Fe, Mn, Cr-containing phases in Al-Si cast alloy

As a common detrimental element in Al-Si cast alloy, Fe can be effectively removed by Fe-containing intermetallic separation in the alloy melt. However, the thermodynamic formation mechanism and growth morphology evolution of high separable Fe-containing intermetallic have not been investigated and clarified in detail until now. In this study, thermodynamic calculation, three-dimensional (3D) growth morphology and crystal structure were characterized to investigate the effect of Mn and Cr on morphology evolution, crystal structure and precipitation temperature of Fe-containing intermetallics. It is demonstrated that the addition of Mn and Cr can increase the precipitation temperatures of Fe-containing intermetallics in melt, and also result in the variation of crystal structures from monoclinic gamma-AlFeSi to cubic alpha-AlFeMnCrSi phases. Moreover, the addition of Mn and Cr significantly changes the morphology of Fe-containing intermetallics from plate-like to cubic shapes. alpha-AlFeMnCrSi phase precipitated at high temperature exhibits the same structural basis as alpha-Al9Mn2Si2. The Fe containing phase of cubic structure provides higher thermo stability which is in favor of its sufficient precipitation and separation.

Automated summary

The addition of Mn and Cr increases the precipitation temperature and changes the morphology of Fe-containing intermetallics from plate-like to cubic shapes. The cubic structure of alpha-AlFeMnCrSi phase provides higher thermo stability, facilitating its sufficient precipitation and separation.