Characterization of the double oxide film content of liquid aluminum alloys by computed tomography

Abstract

The entrainment of the surface oxide layer of aluminum alloy melts is currently a mostly inevitable process during the melt handling and processing techniques of the foundry industry. As a consequence, a large number of double oxide films (bifilms) are often incorporated into the melts, which bifilms can act as initiation sites for pore formation during the solidification of the alloy. In this study, this relationship between bifilms and pores was examined in the case of an Al-Si-Mg-Cu based alloy. The entrained oxide film content of the melts was characterized by the analysis of the fracture surfaces of K-mold specimens, Bifilm-Index measurement and X-ray computed tomography (CT) of reduced pressure test (RPT) samples, which can be considered as a new method of melt quality characterization. It was found that the number of oxide films found on the fracture surfaces of K-mold specimens is proportional to the number density of pores found in RPT samples. Investigations with scanning electron microscopy (SEM) revealed that oxide films can be found on the inner surface of the pores in RPT samples, which confirms the theory, that pores and bifilms are interconnected phenomenon. Based on the results, the bifilm content and so the quality of aluminum melts can be characterized using CT analysis of RPT samples.