A Quantitative Evaluation of Degassing Duration on Bifilm Index and Mechanical Reliability of AlSi9Cu3 Alloy

Abstract The influence of degassing duration on melt quality and mechanical reliability of AlSi9Cu3 alloy was systematically investigated under controlled experimental conditions. Degassing treatments of 0, 3, and 6 minutes were applied, and melt cleanliness was evaluated using reduced pressure test (RPT)-based bifilm index measurements and X-ray radiography. Mechanical performance was assessed through tensile testing and further analyzed using Weibull statistics to quantify reliability. The results show that degassing duration significantly affects both porosity characteristics and the statistical distribution of mechanical properties. The 3-minute treatment led to reduced internal porosity, lower bifilm and density index values, and narrower Weibull distributions, indicating improved consistency and reliability. Although the 6-minute condition resulted in a slight increase in ultimate tensile strength, it was accompanied by increased scatter, suggesting reduced process stability. The findings demonstrate that mechanical behavior is governed by defect severity rather than defect quantity and that extended degassing does not necessarily yield proportional improvements. By establishing a direct relationship between bifilm index and Weibull-based reliability parameters, this study provides a comprehensive framework for evaluating melt quality beyond conventional average-based approaches.