Influence of wood hardness on the shear strength performance of friction stir spot welding joints with a Nylon-66 interlayer

To address the challenge of interfacial incompatibility and brittle failure in wood-metal hybrid structures, this study investigates a friction-based joining method using Nylon-66 as a thermoplastic bridging agent between AA6061 aluminum alloy and various wood species. The joints were fabricated via Friction Stir Spot Welding techniques, focusing on the mechanical interlocking and chemical bonding facilitated by the nylon interface. The research revealed that the optimized AA6061-Beech joint achieved a peak shear tensile strength of 10.43 MPa. A transition from brittle separation to a controlled, ductile-like failure mode was discovered. Unlike conventional joints, the nylon-bridged interface maintained a sustained load-bearing capacity exceeding 400 N even after the initial peak load. This phenomenon is attributed to the elongation of the nylon bridge, which effectively absorbs energy and prevents sudden structural collapse. This study demonstrates that thermoplastic bridging is a viable strategy for creating high-strength, safety-enhanced wood-metal joints for green manufacturing.