Hot forming characteristics of magnesium alloy
The forming property of magnesium is much better than that under the cold state. Therefore, the forming of the workpiece is mostly in the hot state, and the forming method and the heating equipment are the same as the aluminum and copper alloys. Of course, the tools and the process parameters are different.
Magnesium alloy slate can form quite complex workpiece at high temperature without annealing. Therefore, the working procedure is less, the forming time is short, the working die is simple, the work piece is small, and the shaping is not needed after forming. The workpiece size deviation is much smaller than that of cold forming, and the mechanical properties will not decline.
Selection of sheet material
The plate is rolled and extruded. It is best to choose the rolling and O state, because it has a high performance price ratio, and the choice of the thickness range is large, and it can also be used in H24 state. It is better to do some experiments before forming to determine the best heating temperature and heating holding time.
Thermal expansion effect
The coefficient of linear expansion of magnesium and magnesium alloys (the average value of 20 ~300 C) is 28.1 x 10-6m/m) much larger than that of iron. For example, the coefficient of linear expansion of iron is only 11.9 x 10-6m/m at 100, and magnesium is 1.36 times larger than that of iron, so it is necessary to consider the difference between them when forming a magnesium alloy with steel or die casting to ensure the stability of the size. No, no. However, the linear expansion coefficient of magnesium alloy is not very different from that of aluminum alloy and zinc alloy. When these two kinds of alloy die are formed, they can be corrected without size factor.
Before forming heating, the sheet should be treated to remove all foreign objects on the surface. Mold, punch and so on should also be clean. Solvent cleaning tools can be used.
The forming slab and the forming die must be heated. The heating equipment is heating board, heating furnace, electric heater, heat transfer liquid, induction heater, light bulb and other infrared heaters. Infrared heating is a group of infrared heating, simple process and low cost. When the heat transfer fluid is usually heated for oil, the hot oil is circulated in the die channel. The maximum temperature is 175 degrees C. The heat transfer fluid heating equipment has the carburetor, the circulation machine and the temperature control system.
When the magnesium alloy is hot forming, the temperature should be strictly controlled. When a small amount of parts is produced, the temperature can be monitored and controlled by the contact thermometer. In batch forming, it should be automatically controlled so as to control the temperature more accurately.
The lubrication of hot forming is more important than cold forming because magnesium alloys are more susceptible to surface damage under thermal condition. The selection of lubricants is mainly determined by the forming temperature. The choice of lubricants are mineral oil, animal oil, grease, soap, wax, molybdenum, colloidal graphite, thin paper and glass fiber. Which lubricants are chosen mainly depending on the forming temperature.
When the forming temperature is below 120 C, grease, animal oil, soap and paraffin wax can be used. When spinning, the lubricant should stick to the workpiece so as to avoid centrifugal force throwing the lubricant out. The lubricant used should be easy to remove after forming. The forming temperature is higher than 120 C, and ordinary grease, grease and paraffin can not be used. Colloidal graphite can be used. When the temperature reaches 230 degrees, it can be lubricated with soap. When the forming temperature is higher than 230 degrees, colloidal graphite, secondary molybdenum and graphite alcohol mixture can be used. After forming, the lubricant on the workpiece should be removed as soon as possible so as to avoid corrosion and long time. It is not suitable for lubricants to be lubricated with thin paper or glass fiber and placed between tools and workpieces.