Research On The Cracking Mechanism Of Magnesium Alloy During Hot Plastic Forming

Magnesium alloy is the lightest metal structural material. It is widely used in civilian vehicles and military weapons. At high temperature the mechanical properties and corrosion resistance of magnesium alloy are low are low, and the application of it is limited. So far, plastic forming is an effective method to improve the mechanical properties of magnesium alloys, especially the mechanical properties of magnesium alloys can be improved greatly after severe plastic deformation.High strength heat resistant Mg-Gd-Y-Zn-Zr magnesium alloy has a good application prospect in the aerospace industry. AZ80 magnesium alloy is widely used in automobile parts. In this paper, thermal simulation compression test and tensile test are conducted for the cylindrical specimens, cone specimens, in situ tensile specimen(0 °, 45° and 90°) and notched tensile specimens(R = 0, R=5 and R=20) at different temperatures(350 ℃, 400 ℃and 450 ℃).The fracture mechanism of magnesium alloy at different temperatures is different. Through the method of compression test, tensile test, metallographic and scanning microstructure to analyze magnesium alloy mechanical properties and the fracture microstructure. Under normal circumstances, the elongation of magnesium alloy increased as the temperature rose, but there were some exceptions. This is on account of the gap strengthened changing the stress distribution and the driving force of the fracture, so that the fracture of specimen occurred earlier. Therefore, the fracture strain of magnesium alloy containing rare earth is larger than that of AZ80 magnesium alloy at high temperature.The fracture mechanism of high temperature deformation of magnesium alloy was verified by scanning electron microscope. In high temperature compression, the fracture mechanism of the cylindrical and conical samples was different. Compared with the fracture mechanism of AZ80 magnesium alloy, the fracture mechanism of rare earth magnesium alloy is from dimple fracture to shear fracture. Fracture strain became larger, and the plastic was better. With the increase of situ tonsile degree for sheet specimens, stress of three axis angle became smaller, the shear fracture mechanism enhanced, fracture displacement became larger, fracture strain enhanced. The fracture mechanism varied among different sizes of gaps in the notched tensile. As we all know, In plastic processing, magnesium alloy forging cracking often occurs, can predicted crack mode, to provide theoretical basis for the prevention of forging cracking.