Microplasma oxidation technology
Microplasma oxidation, also known as micro-arc oxidation, is an advanced surface treatment technology that electrochemically grows ceramic films in situ on the surfaces of light metals such as aluminum, magnesium, titanium, and their alloys. This technology overcomes the performance limitations of traditional anodic oxidation. By inducing plasma discharge under a high-voltage electric field, complex physical and chemical reactions occur on the metal surface, forming a ceramic oxide film that is firmly bonded to the substrate. Compared to traditional anodic oxide films, microplasma oxide films offer significant advantages, including greater thickness (5-100μm), higher hardness (HV500-1500), and enhanced corrosion resistance. Furthermore, the film is metallurgically bonded to the substrate, achieving a bond strength exceeding 50MPa, far exceeding the 10-20MPa of anodic oxide films. Since its introduction in the 1980s, this technology has demonstrated significant application potential in aerospace, automotive, medical device, and other fields, becoming a key method for strengthening light metal surfaces.
The core advantage of microplasma oxidation technology is that it can generate ceramic films in situ on metal surfaces without the need for additional coating materials, and the film properties can be flexibly controlled through process parameters. By adjusting parameters such as electrolyte composition, voltage, current density, and processing time, ceramic films with different compositions and structures can be prepared to meet diverse performance requirements. For example, on the surface of aluminum alloys, the use of silicate electrolytes can generate oxide films mainly composed of α-Al₂O₃ and γ-Al₂O₃ , which have excellent wear resistance; the use of phosphate electrolytes can generate oxide films containing aluminum phosphate, which are more biocompatible and suitable for medical device applications. On the surface of magnesium alloys, the addition of additives such as fluoride can inhibit the excessive dissolution of magnesium, forming a dense magnesium oxide – aluminum oxide composite film, significantly improving its corrosion resistance. Experimental data show that the corrosion current density of AZ91D magnesium alloy treated with microplasma oxidation in 3.5% sodium chloride solution is reduced from 10⁻⁴A/cm² to below 10⁻⁷A/cm² , and the corrosion resistance is improved by three orders of magnitude.
The equipment system for microplasma oxidation technology is relatively simple, primarily consisting of a power supply, an electrolytic cell, a stirring system, and a cooling system, making it easy to scale up for industrial production. The power supply typically uses a DC or pulsed power supply, with an output voltage range of 50-600V, adjustable to suit different metal materials and film requirements. The electrolytic cell is typically constructed of stainless steel and lined with acid- and alkali-resistant materials. The stirring system ensures uniform electrolyte composition, while the cooling system controls the electrolyte temperature between 20-60°C to prevent excessive temperatures from affecting film quality. Compared to other surface treatment technologies (such as plasma spraying and electroplating), microplasma oxidation technology boasts a shorter process flow, lower energy consumption, and less pollution. For example, to treat one square meter of aluminum alloy sheet, microplasma oxidation consumes approximately one-fifth the energy of plasma spraying. Furthermore, the electrolyte can be recycled, resulting in minimal wastewater discharge, meeting environmental standards. After introducing a microplasma oxidation production line at an automotive parts manufacturer, surface treatment costs were reduced by 30% while also reducing hazardous waste emissions.
The application of microplasma oxidation technology on different metal materials has its own unique characteristics, requiring optimized process parameters tailored to the material’s properties. For aluminum alloys, the microplasma oxidation process is relatively easy to control, forming high-quality oxide films in a variety of electrolytes, making it suitable for most industrial applications. However, for magnesium alloys, due to their high chemical activity and easy dissolution in electrolytes, a low-concentration electrolyte and appropriate pulse parameters are required to minimize matrix dissolution. One study successfully produced a dense oxide film 50μm thick on the surface of AZ31 magnesium alloy using a dual-pulse power supply (600V forward pulse, 100V reverse pulse). For titanium alloys, microplasma oxidation can produce a ceramic film containing titanium dioxide. The introduction of calcium and phosphorus imparts bioactivity to the film, making it suitable for orthopedic implant applications. Furthermore, this technology can be used for surface treatment of materials such as zinc and zirconium alloys, expanding the application range of light metals.
The development trend of microplasma oxidation technology is moving towards functionalization, composites, and intelligence. In terms of functionalization, by doping nanoparticles (such as carbon nanotubes and graphene), composite ceramic films with special properties such as electrical conductivity, thermal conductivity, and antibacterial properties can be produced. For example, a microplasma oxidation film containing silver ions applied to an aluminum alloy antibacterial cutting board can achieve a 99.9% sterilization rate against E. coli. In terms of composites, combining microplasma oxidation with other surface treatment technologies, such as applying an organic coating on top of the microplasma oxidation film, can further enhance corrosion resistance. In one marine engineering application, this composite coating demonstrated salt spray resistance of over 10,000 hours. In terms of intelligence, the introduction of the Internet of Things and artificial intelligence technologies enables real-time monitoring and automatic adjustment of process parameters. For example, an automated production line uses machine vision to inspect the film’s appearance and combines it with an electrochemical workstation to monitor its corrosion resistance online, increasing the product qualification rate from 90% to 99%. With the continuous advancement of these technologies, microplasma oxidation technology will play a vital role in even more fields, promoting the high-performance application of light metal materials.
