Microstructure Formation in a Gas-Atomized Drop of Al-Pb-Sn Immiscible Alloy

Abstract

Al-Pb-Sn alloy is rapidly solidified by using the high-pressure gas-atomization technique. A model describing the microstructure evolution in an atomized drop is developed. This model takes into account the concurrent actions of the nucleation, diffusional growth, spatial motions of the minority-phase droplets, and the solidification of the matrix liquid. The microstructure formation in the gas-atomized drop is simulated by coupling the thermodynamic and kinetic calculations. The numerical results show a favorable agreement with the experimental results. They demonstrate that under the rapid cooling conditions of gas atomization, the spatial phase separation due to the Marangoni migration of the minority-phase droplets mainly affects the microstructure formation in a small region close to the atomized drop surface. All the minority-phase droplets are nucleated during the liquid-liquid phase decomposition period. For an Al-(5-9) wt pct Pb-3 wt pct Sn alloy, the average radius and number density of the minority-phase particles depend exponentially on the powder diameter. The microstructure formation process is discussed in detail.