In-situ study on grain refinement mechanism of Al-13Cu alloys modified by high entropy alloy particles and ultrasonic treatment

This study explores the grain refinement mechanisms of primary α-Al during solidification of Al-13 wt% Cu alloy modified by FeCoCrNiAl high-entropy alloy (HEA) particles via ultrasonic treatment. In situ X-ray radiography combined with machine learning-based computer vision techniques was employed to systematically analyze the nucleation and growth behaviors of α-Al grains. Results indicate a significant grain refinement effect associated with increased HEA particle content and higher cooling rates. Specifically, the addition of 2.0 wt% HEA particles reduce the primary α-Al grain size notably, achieving approximately 213 μm at a cooling rate of 1.0 K/s. At a cooling rate of 0.2 K/s, raising the HEA content from 0.5 to 2.0 wt% markedly increases the maximum nucleation rate (from 8.6 to 30.3 crystals/mm³/s), shortens the time required for grain growth cessation (from 18 s to 10 s). Similarly, at a fixed HEA content (1.0 wt%), increasing the cooling rate from 0.2 K/s to 1.0 K/s enhances the maximum nucleation rate (from 25.7 to 93.9 crystals/mm³/s) and reduces the grain growth cessation time (from 15 s to 9 s). Grain size distributions consistently exhibit normal distribution patterns. The addition of HEA particles significantly inhibits grain growth and reduces solute enrichment during solidification. These findings demonstrate that FeCoCrNiAl HEA particles facilitate grain refinement by effectively promoting heterogeneous nucleation and inhibiting grain growth.