Finite element modeling of superplastic forming of friction stir processed AZ31B mg alloy

Superplastic forming (SPF) is considered to be a near net shape manufacturing technique, mainly adopted to realize aircraft and automotive parts, which requires relatively high tooling and assembly costs. Furthermore the tuning of the process is a non trivial operation since very limited reliable models have been developed to predict the complex geometries obtained through SPF. In such context several researches, based on finite element method (FEM,) have been conducted on the numerical optimization of conventional SPF processes. Friction Stir Processing (FSP) can be used combined with conventional SPF to enhance the superplastic material behavior by means of grain refinement treatment locally performed. From this point of view very few models have been developed to simulate the different superplastic behavior distinguishing the materials after the application of FSP. In this work free bulge forming tests of AZ31B Mg alloy was experimentally performed by means of blow forming laboratory-scale equipment as well as FEM analysis were conducted to simulate the SPF in two different cases: unprocessed and friction stir processed (FSProcessed) condition. The most relevant parameters of the constitutive numerical model were optimized by numerical-experimental comparison. More specifically material strength factor (K) and strain rate sensitivity index (m) were considered during the parametric optimization. Strain and thickness distributions were compared to the experimental measurements in order to individuate the optimized constitutive equations governing the superplastic behavior in both case studies.