Tribo-characteristic of coated die against magnesium in ironing process

Recently, magnesium alloys are used widely for any parts that are required to be lighter. Plastic formability of magnesium at room temperature is extremely low. Therefore, magnesium is usually formed over 200 degrees Celsius. At these temperatures, it is impossible to use oil lubricants. To realize dies with high tribological performance, it is effective way to apply some kind of thin hard coatings. In this paper, a tribometer, which can evaluate tribo-characteristics of thin hard coatings against magnesium alloy at temperatures between room temperature to 300 degrees C, is newly developed. By using this tribometer, some thin hard coatings, diamond-like carbon (DLC), CrN, TiN, are evaluated. DLC coating exhibits lowest friction coefficient under 250 degrees C, however, over this temperature, friction coefficient increases up to 0.4. The amount of adhesion depends not on the perpendicular load acting on the die but on the temperature. When the amount is large enough, the lateral load exhibits high constant value.