Simulation of Primary Particle Development and Their Impact on Microstructural Evolution of Sc-Modified Aluminum Alloys during Additive Manufacturing

Mohammad Sadegh Mohebbi,Vasily Ploshikhin

doi:10.3390/met11071056

Abstract

The microstructures of additively manufactured Sc- and Zr-modified aluminum alloys are significantly influenced by the nucleation role of solid intermetallic particles in undercooled liquid. To replicate such effects, a precipitation model relying on L12-Al3Sc particles is developed. An initiation criterion is proposed based on the precipitation kinetics of primary particles to address solute trapping under high solidification rates. Avrami’s equation is then used to estimate the progress of precipitation. The model is integrated into a cellular automata (CA) analysis to simulate the resulting solidified microstructure, in that the precipitation model is performed implicitly within the CA cells. It is shown that, in accordance with the experimental findings, the proposed simulation approach can predict the distinct fine- (FG) and coarse-grained (CG) zones at the fusion boundary and the meltpool core, respectively. The model can also deliver the reported enhancement of the FG zone under lower scanning speed and higher platform temperatures. These findings are explained in terms of particle number densities at different meltpool regions. Moreover, a semi-2D simulation with a very small cell size is suggested to address the extremely fine grain structure within the FG zone.

Highlights

Additive manufacturing (AM) of different aluminum alloys typically leads to a microstructure dominated by nucleation close to the fusion boundary [1,2,3]
It is believed that this type of nucleation is caused by solid particles that act as inoculants for α-Al
The solid particles responsible for the fusion boundary nucleation in these alloys are explained through the inhomogeneous liquid between the so-called branching and dissolution temperatures

Summary

Introduction

Additive manufacturing (AM) of different aluminum alloys typically leads to a microstructure dominated by nucleation close to the fusion boundary [1,2,3]. The solid particles responsible for the fusion boundary nucleation in these alloys are explained through the inhomogeneous liquid between the so-called branching and dissolution temperatures. Based on the inoculating effect of such particles, a very remarkable fusion boundary nucleation occurs in the Sc-modified alloys. A similar feature is reported in Zr-modified alloys [3,14] Researchers have explained this mostly through the formation of the primary particles under low solidification rates at the fusion boundary, and solute trapping under high solidification rates in the meltpool center (e.g., [11,14]). This research aims to develop a physics-based model for the evolution of the related particles and their effects on the solidified microstructure during the laser powder bed fusion (LPBF) process. In line with the experimental results in the literature, the integrated CA analysis is evaluated under various laser scanning conditions

Material and Models

Evolution of L12 Phase

Integration of Precipitate and Microstructure Evolution into the CA Analysis

Adaptation and Calibration of Parameters

Results and Discussion