Microstructure, Microhardness, and Wear of a Rapidly Solidified Al-20Sn-1Cu Alloy with Bi Addition

Area of Science:

• Materials Science
• Tribology
• Metallurgy

Background:

• Rapid solidification processes like twin-roll casting (TRC) are crucial for producing advanced materials.
• Aluminum-tin (Al-Sn) alloys are widely used but can exhibit poor wear performance, especially under rapid solidification.
• Understanding the role of alloying elements in modifying microstructure and properties is essential for optimizing alloy design.

Purpose of the Study:

• To investigate the impact of bismuth (Bi) addition on the microstructure, hardness, and wear behavior of rapidly solidified Al-20Sn-1Cu alloy.
• To elucidate the role of Bi in modifying the alloy's properties under cooling rates relevant to twin-roll casting (TRC).

Main Methods:

• Alloys with and without 2 wt% Bi were prepared using rapid solidification techniques (stepped graphite mold).
• Microstructural analysis was performed to observe phase morphology and distribution.
• Microhardness testing and wear ball-cratering tests were conducted to evaluate mechanical and tribological properties.
• CALPHAD (Calculation of Phase Diagrams) was used for thermodynamic predictions.

Main Results:

• Bi addition fragmented the interdendritic Sn-rich phase and promoted the formation of finely dispersed Bi-rich regions, confirmed by CALPHAD.
• Microhardness increased with both Bi addition and higher cooling rates.
• Bi significantly reduced wear volume, especially in rapidly solidified samples, improving tribological performance.
• Adhesive wear was the dominant wear mechanism, with evidence of material transfer and minor oxidation.

Conclusions:

• Bismuth (Bi) addition effectively refines the microstructure and enhances the hardness of rapidly solidified Al-Sn alloys.
• Bi addition markedly improves wear resistance, making it a viable strategy for optimizing Al-Sn alloys produced via TRC.
• The findings highlight Bi as a beneficial additive for enhancing the tribological performance of Al-Sn alloys under conditions relevant to industrial casting processes.