Hot forming characteristics of magnesium alloy

magnesium material in the hot state is much better than that in the cold state. Therefore, the forming of the workpiece is mostly carried out in the hot state, and the forming method and heating equipment are also the same as those of aluminum, copper and other alloys. Of course, the tools and process parameters used are different.

magnesium alloy lath can be stretched at high temperature to form quite complex workpieces without annealing. Therefore, the working procedure is less, the forming time is short, the die used is simple, the workpiece springback is small, and the forming does not need to be reshaped. The size deviation of the workpiece is much smaller than that of cold forming, and the mechanical properties will not decrease. The heating specifications for hot forming of magnesium alloy sheet are shown in the table below.

sheet metal selection

sheet metal has rolled, extruded, preferably rolled and O state, because it has high cost performance, and can choose a wide range of thickness, can also be used in H24 state. It is best to do some tests before forming to determine the best heating temperature and heating time.

Thermal expansion affects the linear expansion coefficient of

magnesium and magnesium alloy (average value of 20 ℃ ~ 300 ℃) is 28.1 × 10-6 m/m) much larger than that of iron. For example, at 100 ℃, the linear expansion coefficient of iron is only 11.9 × 10-6 m/m, while that of magnesium is 1.36 times larger than that of iron, therefore, when forming magnesium alloys with steel or casting molds, this difference must be considered in order to ensure dimensional stability. However, the linear expansion coefficient of magnesium alloy is not much different from that of aluminum alloy and zinc alloy, and the size coefficient can be modified when the two types of alloy molds are formed.

Pre-Treatment

Before forming and heating, the sheet metal should be treated to remove all foreign objects on the surface. The die, punch, etc. should also be clean, and solvent cleaning tools can be used.

heating forming slab and forming die should be heated. The heating equipment includes: heating plate, heating furnace, electric heater, heat transfer liquid, induction heater, bulb and other infrared heaters, etc. Infrared heating is a set of infrared heating, the process is simple, the cost is low. When the heat transfer fluid is usually heated by oil, the hot oil circulates in the mold channel with a maximum temperature of 175 ° C. The heat transfer fluid heating equipment includes a vaporizer, a circulating machine and a temperature control system.

magnesium alloy hot forming temperature should be strictly controlled, the production of a small number of parts, the use of contact thermometer monitoring temperature, batch forming, it should be automatically controlled, in order to more accurate control of temperature.

Lubrication The lubrication of hot forming is more important than that of cold forming, because magnesium alloy materials are more susceptible to surface damage in the hot state. The choice of lubricant is mainly determined by the forming temperature. The lubricants available are: mineral oil, animal oil, grease, soap, wax, molybdenum, colloidal graphite, thin paper and glass fiber.

When the forming temperature is lower than 120 ℃, grease, animal oil, soap and paraffin wax can be used. The lubricant should stick to the workpiece during spinning to avoid centrifugal force throwing the lubricant out. The lubricant used should be easy to remove after forming; forming temperature is higher than 120 ℃, can not use ordinary grease, grease, paraffin wax, available colloidal graphite. When the temperature reaches 230 ℃, soap can be used for lubrication. The forming temperature is higher than 230 ℃, and the mixture of colloidal graphite-two fluidized molybdenum and graphite-alcohol can be used. After forming, the lubricant on the workpiece should be removed as soon as possible to avoid corrosion and time is not easy to remove. Lubricants can be used when not suitable for the use of thin paper or glass fiber lubrication, put them between the tool and the workpiece.