Comparison of the Effects of Ultrasonic Degassing and Rotary Degassing Processes on the Liquid Metal Cleanliness and Tensile Properties of Aluminum Alloys

Abstract Numerous studies have been published particularly focusing on the liquid metal quality so far; however, this study examines the efficiency of both rotary degassing and ultrasonic degassing processes in relation to mechanical properties by focusing on the metal quality before and after values. Degassing processes are primarily applied to reduce dissolved hydrogen and inclusion content in molten aluminum; however, in this study, hydrogen content was not directly measured, and melt quality was evaluated using RPT-based bifilm index (BI) as an indirect indicator of gas-assisted porosity and oxide-related defects. Therefore, ultrasonic degassing (ust) durations of 90 s to 180 s and rotary degassing (rdt) durations of 5 min, 10 min, 15 min, and 20 min were performed to assess the bifilm index before and after values (ΔBI-mm) and the removal efficiency of bifilms (BI-%), and the tensile properties such as yield and tensile strengths and elongation at break were also measured. Weibull distributions were plotted to measure the repeatability and reliability levels of the processes. Based on the second-order polynomial relationships, yield strength decreased with increasing bifilm index. Tensile strength also generally decreased; however, slight increases were observed in some cases, which may be attributed to the composite-like behavior of bifilms. When the bifilm index fell below approximately 40 mm, the mechanical properties exhibited a relatively stable and reliable behavior compared to higher bifilm index values (e.g., ~ 90 mm).