The malleability of magnesium alloys mainly depends on three factors: alloy solid melting temperature, deformation rate and grain size, therefore, the study of magnesium alloy forging are mainly concentrated in, how to reasonably control temperature range, appropriate selection of deformation rate and the control group, refine the grain size, etc to increase or improve the ability of plastic deformation of magnesium alloys.
Generally, magnesium alloys are forged in the high temperature range below the solid-phase line temperature. If the forging temperature is too low, cracks may be formed and brittle, and it is difficult to carry out plastic processing. Compared with the deformation characteristics at room temperature, the plastic deformation of magnesium alloy at high temperature not only increases the slip system but also the grain boundary slip. Grain boundary slip can provide two other effective slip systems. According to Von Mises criterion, the alloy will undergo high temperature transformation, which is conducive to forming. It is found that the plasticity of magnesium alloy increases significantly when the temperature is above 200℃, and the plasticity increases even more when the temperature is above 225℃. However, when the temperature is too high, especially over 400℃, corrosive oxidation and coarse grain are easy to occur.
Magnesium alloy is very sensitive to the deformation rate. Magnesium alloys show high thermoplasticity at low deformation rate, and the plasticity of magnesium alloys decreases significantly with the increase of deformation rate. But different and aluminum alloy and other material, magnesium alloy forging is one of the features hot forging times is unfavorable and overmuch, every heating forging, strength performance – times, especially before forging high heating temperature and holding time is long, down the extent of the larger, for some of the more complex magnesium alloy forgings to forming, many times should be gradually reduce all the forging temperature.
Practice has proved that fine equiaxed grains can improve the plastic deformation ability of magnesium alloy, and the actual size of the grain is also the main factor determining whether magnesium alloy ingot can be directly forged. So how to control the microstructure and refine the grain is one of the keys to improve the malleability of the alloy.
Post time: Aug-31-2022