Effect of Particle Size and Cooling Rate on the Microstructure and Properties of Al-Cu/Nbb2 Alloys Fabricated by Freeze-Ablation Casting

Abstract

At present, improving the properties of aluminum alloys is generally achieved by increasing the cooling rate of the melt and adding micro-nano particles. How to control the cooling rate of the melt to improve the refining effect of grain refiner is still a difficult problem in the aluminum alloy casting industry. An innovative and environmentally friendly casting process, known as freeze-ablation, was introduced during the preparation of Al-NbB2 intermediate alloy. This process significantly enhances the cooling rate of the melt. The results indicate that the Al-NbB2 intermediate alloy produced under high cooling rates has a noticeable refining effect on Al-Cu alloys, with smaller NbB2 particles demonstrating superior refining performance. The average grain size (AGS) of the refined Al-Cu alloy decreased from 154 μm to 69 μm, the tensile strength increased by 12%, the fluidity increased by 18.4%, and the hot tearing index decreased from 144 to 12. The matching degree between NbB2 and α-Al was calculated using high-resolution transmission electron microscopy and the edge-to-edge model (E2EM). It was found that the atomic interplanar spacing and interatomic spacing mismatch between NbB2's <11-20>plane and Al were both less than 10%, which further proved that NbB2 could serve as an effective nucleation site for ɑ-Al grains to achieve grain refinement.

Keywords: grain refinement, freeze-ablation, particle size control, mechanical properties, process properties