The surface coating formed on aluminum alloy nuts using micro-arc oxidation technology significantly improves their wear resistance. This effect is due to the combined effects of optimized composition, structure, and process. Micro-arc oxidation uses high-voltage electric spark discharge to create a ceramic layer primarily composed of aluminum oxide on the aluminum alloy surface. Its hardness far exceeds that of the substrate, providing a fundamental guarantee for improved wear resistance. The content of the high-hardness α-Al₂O₃ phase in the ceramic layer directly affects wear resistance. By manipulating the electrolyte composition and electrical parameters (such as voltage and current density), the proportion of this phase can be increased, further enhancing the coating's hardness and resistance to abrasive wear.
The porous structure of the coating is another key factor in improving wear resistance. The micropores formed during micro-arc oxidation can store lubricant, creating a self-lubricating effect and reducing the coefficient of friction. For example, adding solid lubricants such as graphite or polytetrafluoroethylene to the electrolyte forms a uniform lubricating film on the coating surface, reducing direct contact wear. This synergistic effect of the structure and lubricant enables aluminum alloy nuts to maintain a low wear rate even under dry friction or boundary lubrication conditions. Optimizing process parameters is crucial to coating performance. By adjusting oxidation time, voltage, and electrolyte system, coating thickness and density can be controlled. A thick, dense layer, serving as the primary load-bearing area, effectively disperses contact stress and prevents coating spalling. A well-defined distribution of surface micropores balances lubricant storage and bonding strength. Furthermore, the use of pulsed power supply modes refines coating grains, reduces crack defects, and further enhances wear resistance.
Composite coating technology offers a new approach to optimizing wear resistance. Combining micro-arc oxidation with spraying, electrodeposition, and other processes allows for the creation of multi-layer functional coatings. For example, a micro-arc oxidation layer serves as a base, upon which hard particles such as tungsten carbide or molybdenum disulfide are sprayed, creating a composite structure of "hard base layer + lubricating surface layer," ensuring both bonding strength and a low friction coefficient. This design performs particularly well under heavy loads or high-frequency vibration conditions.
The metallurgical bond between the coating and the substrate is the fundamental guarantee of wear resistance. During the micro-arc oxidation process, the coating grows in situ on the aluminum alloy surface, forming a metallurgical bond with the substrate, eliminating the flaking problem associated with traditional coatings. This strong bond ensures the coating maintains its integrity during long-term wear, preventing widespread failure even with localized wear, thereby extending the service life of aluminum alloy nuts.
Optimized environmental adaptability further expands the application range of micro-arc oxidation coatings. For corrosive environments such as marine or chemical industries, phosphates or silicates can be added to the electrolyte to form a corrosion-resistant ceramic layer. This coating not only resists wear but also prevents the ingress of corrosive media, preventing accelerated failure caused by the synergistic effect of corrosion and wear. For example, in salt spray tests, the optimized coating significantly extended the service life of aluminum alloy nuts.
The environmentally friendly nature of micro-arc oxidation technology also offers advantages for its industrial application. Compared to traditional electroplating or hard chrome plating, this process does not require the use of heavy metals or highly toxic chemicals, and the electrolyte is mostly a weakly alkaline system, making it environmentally friendly. Furthermore, the process is simple, can be performed at room temperature, and consumes relatively little energy, aligning with the trend toward green manufacturing. These characteristics make micro-arc oxidation coating an ideal choice for wear-resistant modification of aluminum alloy nuts.
