Friction stir spot welding of aluminum and wood with polymer intermediate layers

Lap joints between aluminum and beech ( Fagus longipetiolata ) were obtained via friction stir spot welding with Nylon-66 intermediate layers. The polymer layer was introduced to form sandwich structures, which induced mechanical interlocking through infiltrating into the rough surface and formed chemical bonding via C-O-Al bonds. Wood degradation and residual stress were downgraded due to the buffering of the polymer layer. The maximum tensile shear strength with Φ12 mm circular lap area was 11.2 MPa, indicating that friction stir spot welding with thermoplastic polymer intermediate layers has the potential to join metals and woods with high performances.