Research Of Forming Limit And Spring-Back Of Magnesium Alloy Sheet AZ31 At Warm Condition

Nowadays, with the requirement of low energy-consumption and environmental requirement proposed, lightweight becomes more and more important. Magnesium alloys have become one kind of the most development potential and competitive light metals because of their good properties such as light weight, recyclability and so on. Magnesium alloys exhibit poor formability under room temperatures and their formability can be improved under evleated temperatures. The techniques of warm stamping of magnesium alloys have been paid more and more attentions in recent years due to the reason that it can remarkably improve the production efficiency and the rate of qualified products. The most difficult work in stamping process design is to overcome the drawbacks such as wrinkles, crack and spring-back. In this thesis, AZ31 magnesium alloy sheet was chosen as the material of interest. Forming limits and U-shaped spring-back under warm forming condition were studied by experimental method,theory method and FEM. As for forming limits, it involves FLD and FLSD. First, the moulds for FLD were designed and the FLD experiments under 150℃,200℃and 250℃were finished, FLDs were obtained. Then, the FLD calculating model was established through least-squares fitting based on FLD experimental datum. Futhermore, FLD was transferred to FLSD by combining instability criterion and yield criterion. The FLD and FLSD provide the tool for formability analysis of magnesium alloys stamping.The U-shaped spring-back was studied by using experiment and FEM methods. The moulds for U-shape stamping were also designed and U-shaped forming experiments at isothermal and non-isothermal from room temperature to 300℃were completed. With these experiments, spring-back angles were measured. The CAZACU_BARLAT material model was chosen according to the asymmetry in yielding of AZ31. And then the corresponding material parameters were obtained by least-squares optimization. Last, spring-back finite element model at isothermal was established by using LS-DYNA. The FEM results and experiment results were in good agreement.The study in this thesis revealed some properties of warm forming of magnesium alloys and contributes to the progress of warm forming techniques of magnesium alloys.