Research On Gas Bulging Forming Of AZ31 Magnesium Alloy Sheet In High Temperature

Magnesium alloys has been paid a great deal of attentions in recent years because of its low density, excellent specific strength, specific rigidity and recovery. However the key restriction of magnesium alloys application is poor workability because of hexagonal close packed(hcp) structure. Magnesium alloy sheet can highly fabricate complicate parts which will develop the application of magnesium alloys,such as:overlay,cylinder,case and front panel.Aimed at the application of metal sheet forming, a typical commercial AZ31 magnesium alloy has been selected and the superplastic properties at elevated temperatures together with the microstructural evolution in gas-bulging forming have been studied in this dissertation.In this dissertation, one-stage, two-stage and multi-stage gas bulging forming was researched. The mechanical properties of samples were carefully investigated by gas-bulging forming. The regularity of chief parameters such as effective flow stressσ,effective strainδand strain rate sensitivity m was summarized by measuring height and thickness. As a result, in 673K, the highest m value can get 0.38 and in the condition of 673K,0.7MPa ,the highest height can get 23.4mm,H/d=0.78. In the process of multi-stage gas bulging forming, the effective flow stress is decreased with the effective strain. The optimal superplastic deformation rage of temperatures and strain rates was determined too. The microstructure was analyzed to clarify the superplastic deformation mechanism of rolled AZ31 sheet. Dynamically continuous recrystallization, cavity nucleation and grain boundary sliding is important to gas bulging forming. Especially for grain boundary sliding,it is the principal mechanism.At last ,by using the mold home made by myself ,the flow properties of gas bulging forming in the mold and contribution of thickness was studied carefully. It is concluded that the rolled AZ31 sheet exhibits certain plasticity and can successfully fabricate parts of magnesium alloys by gas bulging forming at 673K, 0.9MPa, in 90min. Strain in thickness is alternative homogeneous than two-stage and multi-stage forming. The strain in dome is smaller than suspended deformation zone. The strain in striking angle in cavity die is the maximal.