Effect of interfacial relative motion behaviors on joint formation in ultrasonic bonding of aluminum and carbon fiber-reinforced thermoplastics

This study elucidates the influence of interfacial relative motion on joint formation and performance during ultrasonic bonding of an AA5182 Al alloy to carbon fiber (CF)/polyphenylene sulfide (PPS). The interfacial vibration behaviors and temperature histories were analyzed under various normal forces to clarify the heat generation mechanism. A critical transition in the dominant heat source was discovered: under 600 N, poor coupling causes intense relative motion at the sonotrode/Al interface (amplitude difference: 40 µm), resulting in a slow temperature rise. The bonding mechanism consists solely of resin adhesion. In contrast, 1200 N shifts this relative motion to the Al/CFRTP interface, triggering a rapid temperature rise to 370°C. CFs penetrate into the Al matrix and form a stronger bonding area. Joint strength analysis reveals that the joint strength (1250 N) is governed by three regions under a high normal force: a central mechanical interlocking region contributing 50% of the total strength, an annular cohesive failure region (30%), and an adhesive failure region (20%). These findings reveal that optimizing the interfacial relative motion behavior is essential for achieving high-performance metal–CFRTP dissimilar joints for lightweight automotive structures. • Analyzes the relative motion behavior between the bonding interface during ultrasonic bonding of aluminum alloys and carbon fiber – reinforced thermoplastics using a laser displacement measurement system. • Clarifies the effect of bonding conditions on the relative motion and joint strength. • Discusses the bonding mechanisms in different bonding regions and their contributions to joint strength.