Solidification of Al12Si Melt Pool in Laser Powder Bed Fusion

Abstract

An understanding of the solidification characteristics of the melt pool during laser powder bed fusion, L-PBF, metal printing is essential to ensure the manufacture of sound parts. This is the main theme of this article where it is attempted to unlock the solidification black box through calculation/measurement of the main solidification parameters of cooling rate, growth rate, temperature gradient, and undercooling. The very small melt pool size and its rapid cooling hinder the application of conventional tools to extract such information. A knowledge of these parameters and their effect on the microstructure and morphology of constituent phases could help to better control the L-PBF process and indeed all the fusion-based additive manufacturing routes, to fabricate high-quality parts. Al12Si alloy solidification during the L-PBF fabrication route is examined to highlight the extreme changes in solidification parameters and their effect on the morphology and size of eutectic Si. This is because the morphology of Si controls the mechanical properties of the finished part. The Al–Si eutectic has a divorced architecture attributed to the difficulty associated with Si growth resulted from rapid solidification. The generation of a temperature gradient of about 7700 °C/mm resulted in cooling rates in the range of 1.1 × 106 °C/s and a growth rate of 140 mm/s. Such values were then used to predict the morphology of eutectic Si based on the traditional approach.