Dry circular cup deep-drawing of AZ31 magnesium alloy sheet with DLC coating

Magnesium alloys have several advantages which make them attractive for use in structural applications such as: high specific strength, ease of recycling and electromagnetic shield capabilities. There are, however, a few disadvantages associated with manufacture using magnesium alloys such as the fact that it is practically impossible to apply conventional metal forming techniques at room temperature without causing defects. In this study, a methodology of coating the surface of the alloy with a Diamond Like Carbon (DLC) coating in order to increase the surface lubrication is discussed. The DLC acts as a lubricant during the forming process, consequently it is easy to deform the workpiece. Friction tests and deep-drawing tests were carried out in order to estimate the effect of the DLC coating on the formability of the magnesium alloy. In both cases the performance of DLC-coated workpieces were compared to the performance of non coated workpieces using traditional lubricants. The friction tests were used to quantify the change in friction when using the DLC method. Deep-drawing tests were conducted at 200°C and the formability for each condition was measured at each temperature. It was concluded that the use of DLC-coated blanks produces an improvement in formability of magnesium alloys compared to more traditional lubrication techniques.