THERMAL MODELLING AND CHARACTERIZATION OF WIRE ARC ADDITIVELY MANUFACTURED 4043 ALUMINUM ALLOY

Abstract

In this study, a 3D finite element-based numerical model of Wire Arc Additive Manufacturing (WAAM) at part-length scale (macroscopic scale) is developed to study the thermal behaviour of a thin wall. Additionally, a wall of height of approximately 110 mm and thickness of 15 mm was fabricated using the controlled dip short-circuiting method, commonly referred to as cold metal transfer(CMT), in a layer-by-layer manner. The feedstock material was a wire of 4043 alloy, i.e., Al-Si(5.6 wt.%) based alloy. Each layer of the wall is subjected to multiple thermal cycles during the subsequent layer depositions. The thermal cycles, temperature gradient and cooling rate can be predicted using a thermal model. The thermal model, containing up to 10 layers with a layer height of 2 mm, was developed using COMSOL Multiphysics 6.2 software. In the model, the thermo-physical properties of the 4043 alloy were assumed to be temperature-dependent. The element activation method was used to consider the material deposition. The top layer was subjected to the heat source from the welding torch, which was assumed to be a double ellipsoidal volumetric heat source (Goldak’s model). Thermal analysis of these activated elements for heat flow by conduction, convection, and radiation is performed. The model was validated with both the existing literature as well as from the microstructural evaluation of the fabricated wall. Thermal profiles of layers affect the defect formation, in particular porosity. Interlayer formation, i.e., remelting of the previous layer, is observed both from the microstructural characterisation and the results of the thermal model. The interlayer is found to affect porosity size and distribution; from experiments. Interlayer thickness was found to increase with the build direction both from the experiments and the thermal model. Process parameters such as heat input, travel speed and dwell time were varied with the aim to obtain uniform interlayer thickness and hence homogeneity in the build. The outcome shows that the process parameters can be tailored to obtain a deposit with more gradual increase in the interlayer thickness. With the combination of varied parameters a final model was developed, with these parameters a build with the required microstructural properties can be deposited.