When traditional hard anodic coating (HA coating) is not satisfactory with the properties, such as corrosion resistance, wear resistance, fatigue strength, impact resistance, or erosion resistance, etc.), micro-arc plasma oxidation (MAPO) offen acts as an excellent substitute for HA coatings. The comparison between MAPO and HA is listed as following:
The comparison between micro-arc plasma oxidation and hard anodic hard coating of aluminum.
Item |
MAPO |
HA |
Voltage and Current |
High voltage and curent denstiy |
Low voltage and current density |
Deposition rate |
Fast(1~2μm/min) |
Slow |
Working Temperature |
Ambient Temperature |
Low temperature (<5oC) |
Electrolyte |
Alkaline solution (Eco-friendly) |
Acid solution |
Process |
Degrease→MAPO |
Degrease→alkaline clean→Acid pickling |
Oxidation mechanism |
Chemical/electrochemical oxidation, plasma high temperature oxidation |
Chemical/electrochemical oxidation |
Microstructure |
Amorphous and crystalline phase ( α- Al2O3 and γ- Al2O3 ) |
Amorphous |
Hardness |
High (~Hv1500) |
Low (Hv600 max) |
Wear resistance |
Excellent |
Fair |
Toughness of Coatings |
Good |
Poor |
Flexibility |
Excellent |
Poor |
Fatigue strength |
Good |
Poor |
Corrosion resistance/ thermal protection |
Excellent |
Good |
Microstructure |
Inner condense layer and outer porous layer |
Columnar porous layer and very thin barrier |
Alloy choice |
Feasible for various kinds of Al alloys |
Limited |
Fire resistance |
Good |
Poor |
UV durability |
Excellent |
Good |
Dielectric strength |
Excellent |
Fair |
Color |
Limited |
Varity with good appearance |
Cost |
High |
Low |