Tribological Characteristics of Pulse-Anodized Layers on Aluminum

Abstract

This study develops advanced electrochemical synthesis methods for high-performance hard anodic coatings on Al-Cu-Mg alloy (AA2024/D16) substrates. The research systematically investigates the synergistic effects of chemical electrolyte modification via hydrogen peroxide or ozone additions, high-voltage pulse hard anodizing (PHA) modes, and post-synthetic thermal treatments on the coating kinetics and phase composition. It was established that lowering the electrolyte temperature to -5 °C suppresses acid-induced chemical surface dissolution, promoting the steady growth of a dense monohydrated boehmite phase (Al₂O₃⋅H₂O) with significantly enhanced microhardness. Conversely, elevating the synthesis temperature above 0 °C triggers a structural phase transition toward a trihydrated gibbsite phase (Al₂O₃⋅3H₂O). Tribological evaluations under dry sliding and boundary lubrication conditions (mineral and synthetic oils) revealed a unique self-lubricating mechanism: the lower-hardness gibbsite phase undergoes mechanical shearing during sliding contact and forms a continuous, self-replenishing tribo-transfer solid lubricant film on both steel and ceramic counterfaces. The pulse modulation effectively mitigates local thermal concentrations within the pore channels, enabling optimal tribomechanical responses under diverse wear modes. Objective: To enhance the durability of aluminum alloys using surface engineering methods. Research methodology: A novel approach involving pulse-mode anodizing was employed to form a surface layer on the aluminum alloy; the physicochemical properties and wear resistance of this layer under friction conditions were investigated. Scientific novelty: Synthesis conditions and electrolyte composition were determined for forming an anodized layer with a specific phase composition. Practical significance: Pulse-mode anodizing and heat treatment ensure improved wear resistance of the aluminum alloy