Effect of NaF Additive on Energy Consumption and Coating Properties in Micro-arc Oxidation of Aluminum Alloy

In the process of achieving the goal of automotive lightweighting, aluminum alloy has become an indispensable key material with its excellent characteristics, but their insufficient surface properties often require enhancement through technology modification. Micro-arc oxidation (MAO) , as an effective surface treatment technique, can in situ grow high-performance ceramic coatings on aluminum alloy surfaces. However, the high energy consumption limits its industrial application. In this paper, by regulating the NaF concentration in the electrolyte, the effects on the MAO discharge characteristics, coating structure and performance, and MAO energy consumption were systematically investigated. The results showed that the addition of NaF significantly reduced the breakdown voltage, and the unit energy consumption decreased with the increase of NaF concentration, in which the unit energy consumption of the 10g/L NaF system (MF10) was reduced by about 52. 2% compared with that of the unadded system (MF0) . The coating morphology showed that the moderate amount of NaF could reduce the coating pores and enhance the densification, while the excessive amount of NaF led to large pores and surface ablation. XRD analysis showed that NaF promoted the generation of α-Al2O3, mullite, and AlF3 phases. Coating performance tests showed that the corrosion current density of the MF10 samples was as low as 2. 50×10-8 A·cm-2 and the minimum abrasion depth was obtained in friction tests. This study provides a theoretical basis and technical reference for the development of a low-energy and high-performance MAO process for aluminum alloys.