Study On Forming Performance Of AZ31 Magnesium Alloy Sheet

Magnesium alloy is the lightest metal material in engineering field. It is honored as green engineering material for its low density, high specific strength, high specific rigidity,well cutting processing property, well electromagnetic shielding property, heat radiation and easy to recycle. However, due to the poor plastic properties at room temperature, it is difficult to work forming at room temperature for the magnesium alloy. And during the heat process, components are oxidized over high temperature.Many researches have been engaged in the formability of magnesium alloys sheet all over the world. Most of them are concentrated on sheet with thickness above 1mm, less is below 1mm and scarcely below 0.5mm. In this thesis, thin sheet with thickness 0.5mm is taken to study its forming properties. And the forming technology of magnesium at room and high temperature are investigated.Firstly, symmetry and asymmetry rolling were employed to prepare AZ31 magnesium alloy thin sheet of 0.5mm thickness which were fabricated on six-roller mill magnesium alloy engineering & technology center and the microstructure of the two kinds of rolling sheet are observed. Secondly, explore the optimum heat treatment process and one way tensile tests were carried out on AZ31 magnesium alloy sheets prepared by two rolling process and measure the index of punching ability including yield-tensile ratio, yield strength,strain harden exponent, plastic strain ratio and so on at different temperatures. By comparative analysis, the relationship between temperature and punching properties of magnesium alloy. At last experiments of room temperature drawing, high temperature drawing, erichsen cupping and FLD were measured to analyze the properties of magnesium alloy at room and high temperature. The result is following:(1) The grain distribution of AZ31 magnesium alloy sheets made by asymmetry rolling craft at room temperature are more even than those made by symmetry crafts. The grains made by asymmetry are more tiny and the basal texture of AZ31 magnesium alloy sheets made by asymmetry craft was weakened, the tensile strength and elongation increased obviously and the mechanical properties got better.(2) With the temperature increasing, longer holding time, the grain of magnesium alloy boards got bigger and the tensile strength of the sheets changed little. When annealing temperature arrived 300℃,static recrystallization appeared and when annealing temperature arrived 350℃ and the holding time was 0.5h, the static crystallization completed. Thebreaking elongation ratio arrived 16.36%. With the temperature increasing or holding time longer, the grain grown on different levels and the elongation ratio began to decrease.(3) At room temperature, compared with asymmetry rolling AZ31 magnesium alloy sheets, the yield-tensile ratio decreased on any direction, value of n increased and the value of r decreased. Little yield-tensile ratio and large value of n benefit to stamping forming but small value of r is not good for stamping forming. At room temperature, the value of LDR of asymmetry rolling sheets is 1.26, which was higher than symmetry rolling. So asymmetry rolling benefits to stamping forming. Between room temperature and 350℃, with the temperature increasing, the value of erichsen cupping tended to increase. The value of erichsen cupping is 9.3 which is much larger than that at room temperature(2.2).