Characterization of the Melt Quality for an Al–5Mg–2Fe Alloy With and Without the Addition of a Custom-Designed Flux

Abstract In this work, the effect of a custom-made, Na- and Ca-free flux on the melt quality of an Al–5Mg–2Fe alloy was studied. The composition of the flux mixture was designed based on thermodynamic calculations as well as previous studies. Melt quality was assessed by using (i) reduced pressure tests with density measurements and Bifilm Index analysis, (ii) microscopic investigation of K-mold samples, and (iii) tensile testing. Defects on fracture surfaces and the microstructure of tensile specimens were investigated by optical and scanning electron microscopy (SEM). Tensile data were analyzed via Weibull statistics. Results indicated that flux addition improved melt quality indices and tensile data only slightly, mainly due to the disappearance of old, coarse oxide films from the fracture surfaces of K-mold and tensile specimens. However, further improvements are needed for a more complete elimination of defects to increase the reliability of mechanical properties. This study provides insight into how fluxing treatments can alleviate the contribution of entrainment defects to the degradation of the mechanical properties of Al–Mg–Fe alloys.