Effect of concentration and thickness on tribological performance and stress distribution of polyvinyl alcohol coatings on aluminum substrates

Abstract

This study investigated the tribological performance and stress distribution mechanisms of pure polyvinyl alcohol (PVA) coatings on aluminum (Al) 5052 alloy substrates. PVA coatings were prepared through solution casting at concentrations ranging from 0.1 to 10 wt%, resulting in coating thicknesses from 0.32 to 307 μm. Tribological tests revealed that the coatings prepared at 5 wt% with thicknesses of 44.2–73.8 μm exhibited optimal performance, achieving friction coefficients as low as 0.157–0.158, representing a 76% reduction compared to bare aluminum (0.67). Long-term durability tests under varying loads (50–100 mN) for 10 000 cycles demonstrated that the optimized coatings maintained superior performance across all conditions. Wear track analysis showed that thin coatings below 7 μm suffered from substrate exposure through abrasive wear, whereas excessively thick coatings above 150 μm experienced delamination and severe plastic deformation. Finite element analysis revealed that the PVA coatings reduced the von Mises stress on both the counter tip and substrate by 31–51% through effective stress redistribution. The low elastic modulus of PVA (1.4 GPa) compared to that of aluminum (70 GPa) enables load distribution over wider contact areas, preventing localized damage. The surface roughness decreased from 0.103 μm for bare Al to 0.033 μm for optimally coated specimens, contributing to improved tribological behavior. These findings demonstrate that pure PVA coatings can serve as effective protective layers for aluminum components without the complexity of composite systems, with critical parameters identified for their practical applications.