Enhancing AA6063 stepped clinched joints through ultrasonic post-treatment: Effects on joint geometry,shear strength,and fracture behavior

Abstract

Ultrasonic post-treatment enhances clinched joint performance, but the duration-effect relationship requires clarification. This study applies ultrasonic vibration (0–240 s) to AA6063 stepped clinched joints. Shear strength increased with ultrasonic treatment duration, peaking at 3126.53 N at 180 s, representing a 21.7% improvement over untreated joints. However, a subsequent 3.28% reduction in strength was observed at 240 s, attributable to over-treatment effects. The geometric parameters maintained consistency throughout the treatment process, with interlock values of 0.14–0.16 mm, neck thickness of 0.83–0.89 mm, and bottom thickness of 1.42–1.54 mm exhibiting no statistically significant variation (p > 0.05). Fractographic analysis demonstrates ductile failure characterized by shear dimples, with quantitative assessment revealing a strong positive correlation (R = 0.96) between dimple density and mechanical strength. Ultrasonic treatment significantly modifies dimple morphology, reducing the mean dimple area from 7.88 μm² to 6.18 μm² and the peak Feret diameter from 1.21 μm to 1.02 μm. These microstructural refinements indicate enhanced homogeneity in plastic deformation and stress redistribution, contributing to the observed mechanical improvements. These findings establish a foundation for optimizing ultrasonic parameters in clinching processes.