Investigation of slag formation and transport in high strength low alloy steel during wire arc additive manufacturing

Abstract

High Strength Low Alloy (HSLA) steel components are increasingly produced using Wire Arc Additive Manufacturing (WAAM) because of its ability to produce complex geometries and achieve high deposition rates. However, preventing the formation of surface oxides, known as silicon islands or slag, remains a persistent challenge. This study examines how process parameters can hinder slag formation, growth, and accumulation in HSLA steels during WAAM deposition. The effects of wire feed speed, shielding gas chemistry, and an auxiliary gas trailing shield on silicon islands were examined using a three-factor, two-level experimental design. Samples consisted of sixteen beads deposited in four superimposed layers, with four beads in each layer. Regression analyses based on image processing indicated that slag formation was minimised with low CO 2 content in the shielding gas and auxiliary shield. Reducing the CO 2 content from 20 to 5% decreased slag coverage by 30–50%, while the use of the gas trailing shield reduced slag coverage by up to 30%. Although wire feed speed did not show a significant main effect, its interaction with the auxiliary shield did; furthermore, the auxiliary shield showed a strong interaction with CO 2 . In situ observations further revealed the dynamic behaviour of slag and its apparent dependence on both the slag content of the underlying layer and the gravity-induced distortion of the molten pool. These findings enhance understanding of the mechanisms that may influence slag formation and provide practical recommendations for reducing slag formation in WAAM-fabricated HSLA steel components.