Effects of mechanical stirring and vibration on the microstructure of hypereutectic Al-Si-Cu-Mg alloy billets

A hypereutectic Al-Si-Cu-Mg alloy billet was fabricated by a semi-solid forming method that combined a simple mechanical stirring treatment with the vertical semi-continuous casting process. Higher rotational speeds and higher casting temperatures during stirring yielded a finer as-cast structure and more uniform distribution of primary silicon particles in the matrix. However, these stirring conditions also led to transverse cracks on the billet surface. A mechanical vibration treatment using smaller amplitudes and lower frequencies during casting improved the cracked surface considerably, resulting in a structure comparable to that of the billet stirred at the same time.