A Study on the Evaluation of Ultrasonic Propagation Properties and Nonlinearity According to Temperature Changes of Aluminium Alloys for Each Aluminium Alloy by Temperature

Aluminium alloys are widely used across various industrial sectors due to their suitability for enhancing structural safety and reducing weight, thereby improving operational efficiency. This study investigates the feasibility of using ultrasonic techniques as an alternative to thermistors for temperature monitoring in electric vehicle motors and batteries. The extent to which ultrasonic maximum amplitude and propagation velocity are temperature-dependent was examined, and the material nonlinearity was analyzed. Step-wedge specimens of Al3003, Al6061, and Al6063—commonly used in electric vehicle components—were fabricated with thicknesses of 4, 6, 8, 10, and 12 mm to examine thickness-dependent behavior. Although the three alloys differ in composition and mechanical properties, their ultrasonic propagation characteristics were found to be highly similar. As temperature increased, ultrasonic attenuation increased while propagation velocity decreased. For intact specimens, nonlinearity increased with temperature. However, the variation remained constant beyond a certain temperature range. In contrast, tensile-fatigued specimens showed increased nonlinearity with fatigue cycles, and the variation decreased at elevated temperatures, producing a more pronounced nonlinear response. These findings suggest that ultrasonic techniques may provide a cost-effective solution for temperature measurement and defect diagnosis, potentially replacing high-cost thermistors currently used in electric vehicles.