Constructing solidification microstructure selection map for AlSi10Mg alloy processed by laser powder bed fusion

Abstract

The cellular structures, which consist of cells and eutectic networks at the cell boundaries, determine the mechanical properties of the Al–Si alloys fabricated by laser powder bed fusion (L-PBF). Therefore, it is scientifically interesting and technologically important to establish the relationship between cellular structures and processing parameters, which is applicable to all kinds of processing methods involving rapid directional solidification, such as L-PBF. In this work, a rapid solidification microstructure selection map (SMSM) of the Al–10Si system in temperature gradient (G)–solidification velocity (V) space is constructed by a synergistic calculation with dendritic and eutectic growth models compatible to the L-PBF process. Considering that the divorced eutectic reaction should occur as the width of the liquid film entrapped in the α-Al cell boundaries becomes smaller than the Al–Si eutectic spacing, the G–V domain suitable for acquiring the cellular structures decorated with divorced eutectic Si networks is determined on the SMSM. The microstructure evolution trends predicted by the SMSM are well consistent with those in the L-PBFed AlSi10Mg melt pools with different processing parameters. The length scales of actual microstructures observed by the experiments from this work and the literature are quantitatively compared to those estimated by the SMSM, and the experimental results are basically in accord with the SMSM. It is demonstrated that divorced eutectic Si networks prefer to form at the bottom of the melt pool, where G is large (> 5 × 106 K/m) and V is small (3 × 10−4–6 × 10−3 m/s) in the SMSM. The outcomes of this work may provide fundamental guidance for tailoring the microstructures of the L-PBFed Al–Si alloys for achieving optimal mechanical properties.