Numerical Simulation And Experimental Study On Superplastic Air-bulging Of AZ31 Magnesium Alloy Heart-shaped Part

Magnesium alloy is one of the lightest of those alloys used as the basis of constructional materials. Its specific weight is small, and only two thirds of the aluminum alloy, one thirds of the titanium alloy. It is excellent in strength/density ratio, rigidity/density ratio and dimensional stability. And magnesium alloy is characterized by electromagnetic shielding, transcalent and recyclable. Magnesium is widely used in the fields of aerospace, automotive, communication and electronic industry. However, magnesium alloys generally exhibit poor workability because of hexagonal close packed (HCP) structure. It is difficult to fabricate hollow shell magnesium alloys parts by conventional plastic forming. Therefore, there will be more practical significance on its practical application to the expansion of the scope of a more complex shape of magnesium alloy parts, whether or not it has superplasticity study under certain conditions using superplastic bulging forming.In this paper, numerical simulation of constant strain rate superplastic bulging of AZ31 magnesium alloy heart-shaped part was analyzed with the finite element analysis software MSC.MARC. With structural superplasticity theory and viscoplasticity/rigid-viscoplasticity finite element method, the air-bulging process of AZ31 magnesium alloy heart-shaped part, the thickness distributions of the bulging parts and the influences of temperature and strain rate on the bulging process were studied and the optimal model was obtained within 20 groups of simulation parameters designed.The air-bulging die was designed for experimental study of AZ31 magnesium alloy heart-shaped part, and the superplastic air-bulging experiment was carried out successfully with the temperature and pressuring curve obtained from the optimal model in the numerical simulation. Then the thickness distributions of the bulging specimen were analyzed and compared with the simulation results, and obtained the influence tendency of numerical model accuracy,process parameters and experimental conditions on the air-bulging process of AZ31 magnesium alloy heart-shaped part. So the result can used for predicting forming defect and guiding bulging experiments.Meanwhile, 16 samples were made along the bulging specimen's symmetrical section and its up-corner section to investigate how the microstructure of AZ31 magnesium alloy heart-shaped part changed during the air-bulging process. The average grain sizes of the samples were measured with linear intercept method, and the results showed that grain size was increased in each sample point. After further analyzing, the growths of grains were related to bulging height, thickness reduction and surface curvature of the sampling points.