Abstract
Different processes are currently being used to weld and join aluminum and copper in
a multilayered configuration in battery pouches for the automotive industry. The
methods differ from one car manufacturer to another, but the most used are
mechanical joint, ultrasonic welding, laser welding, and resistance spot welding.
However, these techniques have limitations such as added mass, cracks, intermetallic
compound formation, and thermal conductivity. Refill Friction Stir Spot Welding (Refill
FSSW) is an alternative process for welding overlap joints. In this work, the
microstructure and properties of a multilayered weld of AA2024/CP-Al produced by
refill FSSW were investigated. CP-Al foils and AA2024 sheets with thicknesses of
0.013 mm and 0.3 mm, respectively, were used. Statistical analysis was conducted to
assess the influence of processing parameters on the joint's mechanical properties,
process temperature, contact resistance, and microstructural features. Specimens
with up to 50 layers of CP-Al foils were successfully welded. Response surface
methodology indicated that plunge speed was significantly influential to LSS and
process temperature; plunge speed was found to influence process temperature
significantly, and rotational speed showed no influence in any of the investigated
properties. The one-factor-at-a-time analysis showed that plunge depth, plunge
speed, and rotational speed alter the AA2024 island's morphology, the bottom sheet's
deformation, and the number of unbonded interfaces in the center of the weld.
Microstructural analysis depicted intermetallic compounds, eutectic constituents, and
unbonded foils; however, these features were not detrimental to the weld's mechanical
properties. A maximum LSS of 1890 N, and minimum process temperature and
contact resistance of 167oC and 0.183 mΩ, respectively, were found. Therefore,
mechanical properties were superior to aerospace application requisites, and contact
resistance values are smaller than conventional lithium-ion batteries' internal
resistance. Infrared analysis showed that temperatures below 80oC are obtained at 30
mm from the welding tool, indicating the possibility of using refill FSSW in batteries
while avoiding cell degradation.
