Microstructural Characterization of Rapidly Solidified Al-6.5Si-4Cu Alloy Powders Produced by Gas Atomization

摘要

Rapid solidification processes (RSP) such as gas atomization, can be used to extend the solid solubility limits of iron and silicon in the Al matrix and therefore to increase the formation of metastable crystalline phases or even to change the morphology and chemistry of intermetallic phases. In this work, the microstructure of rapidly solidified Al-6.5%Si-4%Cu alloy powders were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and differential scanning calorimetry (DSC). The alloy was atomized with nitrogen with an estimated flow ratio of gas to metal mass of 2. Powders in different size ranges between 45 and 250 μm were obtained by mechanical sieving the gas atomized powder. Microstructural characterization indicated that the rapidly solidified powders consisted mainly of intermetallic and silicon particles dispersed in the α-Al matrix. The coarser powders contain larger particles of silicon and intermetallic phases than the finer ones and these differences are related to the higher cooling rates in the finer powder particles. Thermal analysis shows that the high thermal undercooling promoted by gas atomization leads to silicon supersaturation in α-Al matrix. Gas atomization promoted the formation of the metastable α-AlFeSi instead of the equilibrium β-AlFeSi intermetallic phase.