Studies on process parameter optimization and surface modification for joint strength enhancement of laser welded Aluminium 5754-Polyamide hybrid joints

Abstract

Hybrid metal-polymer structures offer several desirable features and are often employed in aviation, automobiles, and biomedical industries. Multi-material combinations, such as aluminium alloys and polymers, are increasingly utilized in the aircraft and automobile industries to improve the strength-to-weight ratio of respective parts and components. Various techniques, including adhesive bonding and mechanical fasteners, have been utilized to join sheets of metal alloys and polymers. However, the higher processing time of adhesive bonding and the additional weight caused by mechanical fasteners are the most significant drawbacks of these processes. To circumvent these limitations, laser beam welding is a viable alternative for joining polymer and aluminium alloys. Moreover, in several engineering sectors, there is a strong demand for different metal-polymer joints in lightweight hybrid structures. This research discusses an experimental investigation on laser direct joining of aluminium 5754 and polyamide (PA). The influence of process parameters of laser welding such as laser power, laser welding speed, and laser defocus on the tensile shear load was investigated. Response surface methodology based on the box-behnken design establishes mathematical relationships between control factors and outputs. Validation and optimization experiments were carried out to ensure the feasibility of the model. The findings demonstrate a strong correlation between the predicted and actual values. The findings indicate that the tensile shear load improves by increasing the laser power and decreasing the welding speed. The detrimental effect in tensile shear load is noticed at lower and higher defocus values. A maximum failure load of 1062 N was achieved under the optimal parameter setting of laser power of 1.6 kW, a laser welding speed of 2 mm/s, and a laser defocus of 9 mm. Later surface modifications such as emery sheet grinding, laser ablated dimples, and laser surface texturing, were performed on the aluminium surface to enhance tensile shear load. The surface modification resulted in a variation in surface roughness values between 0.34 µm and 52.7 µm. The result indicates that while using a square texture geometry of grid width of 214 µm, depth of 255 µm, the surface roughness of 27.79 µm, and a depth-to-width ratio of 1.19, a maximum shear failure load of 1563 N is achieved. This work proposes a novel surface laser treatment method for improving the joint strength of metal-polymer hybrid joints.