OPTIMIZATION OF SINGLE-LAP SHEAR STRENGTH OF PEEK-ALUMINUM JOINTS FOR AUTOMOTIVE APPLICATIONS

Abstract

Adhesive bonding reduces weight, increases fuel economy, and lowers emissions. It is a crucial component in the building of automobiles. In comparison to alternative techniques like welding, riveting, and bolting, it also offers a more even distribution of stress throughout the joint, improving structural integrity and endurance. Additionally, adhesive bonding offers protection against corrosion in hydrothermal environments. Aluminum-6061 and PEEK (Polyether Ether Ketone) are promising candidates for such applications. This project investigates the impact of various surface modifications on the strength of adhesive bonding, particularly focusing on laser surface pretreatment. Traditional surface pretreatment methods such as degreasing, grit blasting, and anodizing have been less effective and, in the case of anodizing, environmentally hazardous. Therefore, laser pretreatment is utilized to ablate the surface and induce roughness at both micro and nano scales, promoting better adhesive interlocking. For comparison, conventional methods like grit blasting and phosphoric acid anodizing are also employed. The sequence of treatments included grit blasting, phosphoric acid anodizing, laser pretreatment, and a combined treatment of laser pretreatment followed by phosphoric acid anodizing. Surface characterization techniques such as Scanning Electron Microscopy (SEM), Optical Profilometry, and Contact Angle Measurement were used to analyze morphological changes. SEM analysis revealed that anodizing resulted in microcracks and nanoparticles, laser pretreatment produced micro and nano structures, and the combined treatment generated a beneficial mix of microcracks, micro, and nano structures. Optical Profilometry measured the average roughness (Ra), root mean square of the profiles (Rq), and peak to valley height (Rz) of the treated Al-6061 surfaces. To evaluate the mechanical properties of the adhesive joints between Al-6061 and PEEK, a Single-lap shear test was performed using a Universal Testing Machine (UTM). The combined treatment of laser pretreatment followed by phosphoric acid anodizing yielded the highest bond strength, demonstrating the efficacy of this approach for achieving robust adhesive bonds. The optimum conditions selected from this experiment to enhance the adhesive bonding are laser pretreatment of degreased Al-6061 substrate at 100% power, iii 0.4mm line spacing, 20kHz frequency, and 50mm/s speed, followed by phosphoric acid anodizing at 20V for 60 minutes. Maximum shear strength of 16 MPa was obtained from these conditions. PEEK crystallization behavior was also studied for enhancing the adhesive bond. Maximum crystallinity of PEEK was achievable at 230 ͦC. The effect of crystallinity of was tested for different curing times – 1 hour, 3 hours and 5 hours. Maximum shear strength of 10.1 MPa was achieved with 5 hours curing