Study of Hybrid Adhesive–Mechanical Metal–Composite Joints Created by Thermal Drilling Technology

The aim of the presented study is to verify the possibility of forming hybrid adhesive-mechanical joints between aluminum sheet and PP matrix composites reinforced with carbon and glass fibers using thermal drilling technology. The research responds to weight reduction trends in the automotive and aerospace industries, seeking joining methods that preserve the continuity of reinforcing fibers. The methodology included applying an experimental organosilicate agent to the aluminum, sequential thermal drilling, and an innovative modification of bushing geometry using a 9.3 mm diameter tool. Joint quality was evaluated via tensile shear testing and non-destructive analysis using computed tomography (CT). Results showed that the organosilicate layer significantly increased the load-bearing capacity and adhesion of glass fiber joints. Hybrid joints exhibited higher energy absorption than purely adhesive joints. The proposed bushing geometry modification led to a statistically significant increase in total dissipated energy (by 28% to 37%) and a desired change in the failure mechanism from composite pull-out to bushing shear. CT analysis confirmed the preservation of fiber integrity through radial deflection. Consequently, hybrid joining via thermal drilling with modified geometry effectively utilizes the mechanical properties of metallic materials in multi-material structures.