Analysis of Different Commercial Solid Fluxes Used During the Rotary Degassing Melt Treatment of Casting Aluminum Alloys

Abstract

This work aimed to get a better understanding of the behavior and melt cleaning efficiency of different commercial solid fluxes used in the foundry industry for the treatment of liquid aluminum alloys. This was realized by combining industrial melt treatment experiments with the application of characterization techniques that can provide information about the phase composition and thermal stability of different fluxes. Rotary degassing treatments coupled with flux addition using 5 different commercial fluxes were conducted on batches of EN AC-46000 alloy (AlSi9Cu3(Fe)) melt. The melt quality was assessed by the Qualiflash technique and Bifilm-Index (BI) analysis of reduced pressure test (RPT) samples. The phase composition and thermal behavior of the fluxes were investigated by X-ray diffraction (XRD) and differential thermal analysis (DTA), respectively. Among the 5 fluxes, two had a rather similar phase composition with the main constituents being NaCl, KCl, CaF2, MgF2, Na2CO3·NaHCO·3H2O, Na2SO4, and K2SiF6. These two fluxes, which contain a relatively high amount of fluoride components (about 11mol pct), and had a melting temperature below 600 °C, proved to be the most efficient in improving the melt quality. The Quality Temperature Index (QTI) values and normalized Bifilm-Index (NBI) results of the RPT samples generally showed a similar tendency, but there was only a loose relationship between the two parameters. Discrepancies between the results of different melt quality evaluation techniques can be traced back to their sensitivity to melt quality changes.