| Abstract Scope |
Increasing scrap utilization introduces impurities, inclusions, hydrogen, and oxide bifilms whose evolution depends on alloy composition and processing history. This study proposes a framework that maps impurity and defect-generation mechanisms across melting, holding, fluxing, degassing, filtration, transfer, and casting. Emphasis is placed on clarifying the meaning and limitations of conventional melt-quality indicators, including density index, hydrogen content, porosity, and inclusion indices. Pressure-filtration behavior is evaluated as an indicator of inclusion accumulation. Thermodynamic stability, hydrogen solubility, oxidation, heterogeneous nucleation, and solidification are considered to interpret relationships among these parameters and guide database development. In a preliminary A365 case study comparing virgin-ingot and 100% in-house-scrap melts, their porosity fractions did not reflect the pronounced difference revealed by pressure filtration. The scrap melt exhibited 188.9% longer filtration time and 224.6% greater filtration resistance, together with a 242.2% higher bifilm index. This discrepancy demonstrates the need for complementary, mechanism-based indicators in recycled-aluminum melt-quality assessment. |