Micro-arc oxidation, also known as micro-plasma oxidation or anode spark deposition, is a new technology that puts non-ferrous metals such as aluminum, titanium and magnesium or their alloys in a special electrolyte and directly grows ceramic membranes on the surfaces of metals or alloys through micro-plasma discharge. This is a new method based on anodic oxidation.
According to Shenzhen Electroplating Factory, it is generally believed that the micro-arc oxidation process has gone through four stages.
(1) anodic oxidation stage
When the sample is placed in a certain electrolyte, countless small and uniform white bubbles appear on the surface and cathode of the sample after electrification, and with the increase of voltage, the bubbles gradually become larger and denser, and the generation speed is also accelerated. This phenomenon exists until it reaches the breakdown voltage, which is the anodic oxidation stage.
(2) Spark discharge stage
When the voltage applied to the sample reaches the breakdown voltage, countless tiny spark points with low brightness begin to appear on the surface of the sample. The density of these sparks is not high, and there is no sonic boom. At this stage, the ceramic layer begins to form on the surface of the sample, but the growth rate of the ceramic layer is very small, and the hardness and density are low, so the time at this stage should be reduced as much as possible.
(3) micro-arc oxidation stage
After entering the spark discharge stage, with the rising voltage, the spark gradually becomes bigger and brighter, and the density increases. Subsequently, the discharge spots began to appear evenly on the surface of the sample. The arc spot is large and high-density, which becomes brighter with the increase of current density, accompanied by a strong detonation sound, and then goes to the micro-arc oxidation stage.
(4) Arc extinguishing stage
At the end of the micro-arc oxidation stage, the voltage reaches the maximum, and the growth of ceramic layer will show two trends. One is that the arc points on the surface of the sample become more and more sparse and eventually disappear, and only a few tiny sparks on the surface eventually disappear, and the sonic boom stops. The other is that there are only a few tiny sparks on the surface, which will eventually disappear completely, and at the same time, large arc spots suddenly appear in one or several other parts. These large arc spots are bright and dazzling, can remain motionless for a long time, and produce a lot of gas, and the explosion sound increases.