Determination Of Flow Stress And Friction Coefficient Of Magnesium Alloy Sheet By Reverse Analysis Method

With the development of science and technology, people are more and more strictly with the energy saving and emission reduction. Magnesium alloy now as the most light metal structural material in the world, because of its low density, high strength, good heat dissipation and excellent damping properites, attracts more and more people’s attention. In recent years, the application of magnesium alloy widespread quickly in aerospace, automovie, electronics and other aspects. The flow stress equation and friciton condition of magnesium alloy play an important part in the forming process, especially have the reference value and practical significance in magnesium alloy finite element simulation analysis and product design.This paper using inverse finite element analysis method, solve the AZ31B magnesium alloy’s flow stress equation and the friction coefficient in forming process at250℃. The main works are as follows:Design a set of improved limit dome height experiment device, including the heating facilities in the process of forming and a set of related mold.There are two conventional flow stress test method:one based on the tensile test. In this test, because of necking phenomenon, the flow stress equation is not accurate in the state of large strain. Another method based on the compression test, but for the influence of friction, actually the result is not accurate too. This paper using the finite element reverse method, change the flow stress equation determine problem into optimization problem. Using RSM method to curve fitting for the design variables and objective function. At the end, through optimizing the fitting curve get the flow stress equation of material.The common friction coefficient determination method of metal is suitable for forming, the internal force of workpiece is mainly compressive stress, and the method is usually in normal temperature conditions. For the magnesium alloy sheet, forming usually carried out in certain temperature conditions(approximately150to300℃) and the stress of workpiece is mainly tensile stress. This is different with bulk forming. Based on achieved flow stress equation, proposed a new friction coefficient determine method for sheet forming, this method using currently experimental facility, only need to measure the center hole change of sheet, then can get the calibration curve of friction coefficient. This method is not only suitable for magnesium sheet, but also suitable for normal metal sheet. The result can be used for evaluating the lubricating performance and the data of finite element simulating.