Novel vase-shaped structure fabricated by progressive laser surface texturing for strengthening friction spot joints between 2219 aluminum alloy and PEEK

Abstract

Surface texturing has emerged as a highly effective method for enhancing the interfacial properties of metal-polymer dissimilar joints. In this study, 2219 Al alloy/PEEK joints were fabricated by friction spot joining (FSpJ). Before joining, the 2219 Al alloy was subjected to progressive laser surface texturing using a nanosecond laser source, to create multi-scale interlocking structures to maximize the interfacial strength. Initially, full-power laser pulses were utilized to generate conventional cup-shaped craters through laser ablation. Subsequently, half-power laser pulses were employed to transform these cup-shaped craters into novel vase-shaped craters. During the half-power laser processing, the liquid metal partially solidified on the inwall to form a neck structure, and partially spilled out of the crater and solidified into a lotus-shaped structure encircling the opening. The vase-shaped craters and lotus-shaped structure provided micron and sub-micron interlocking at the interface of joints, with strength surpassing the group in cup-shaped by 28.8 %. Meanwhile, the fracture mode in the lap shear testing shifted from interfacial failure (i.e. PEEK was pulled out from the crater) to cohesive failure in the PEEK material near the interface. C-O-Al chemical bond at the joint interface was formed based on X-ray photoelectron spectroscopy (XPS) analysis. Numerical simulations revealed tensile stress components at the interface during crack initiation, which drove the PEEK structures in cup-shaped craters to pull out through tilting deformation. In contrast, the innovative vase-shaped crater prevented the PEEK pull-out failure by the interlocking effect from the neck structure on the crater's inwall.