Comparative Analysis of Corrosion Resistance Between 424 and 824 Aluminum Beverage Can Lids when Exposed to a Carbonated Cola Beverage: A Blistering Study

This study compares corrosion behavior and blister formation in aluminum can-lid variants 424 and 824 when exposed for 10 days to a pressurized, carbonated cola beverage (40 °C, 90 psi). Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), EIS-derived beverage-uptake measurements, and optical microscopy were used to track coating degradation. Uptake results show that the 824 coating rapidly absorbed liquid, peaking at ≈19 vol % within the first 30 h, whereas the 424-coating stabilized at 3-5 vol % for most of the test. The high uptake in 824 coincided with lower pore resistance (Rpo) and charge-transfer resistance (Rct) and with higher double-layer (Cdl) and coating capacitances (Cco), indicating accelerated loss of barrier properties. No blister formation was detected on the outside surface of 424. The blisters were observed for both the lids in the rivet area and on the outside surface of the 824 lids. The combined electrochemical, uptake, and microscopic evidence demonstrates that variant 424 provides markedly superior corrosion protection under realistic beverage conditions.