The design of a formability test in warm conditions for an AZ31 magnesium alloy avoiding friction and strain rate effects

In this study, a test procedure is proposed to investigate the formability of the AZ31 Mg alloy in warm conditions (below 200 °C) while keeping the equivalent strain rate constant. Both the variables (temperature and strain rate) play a key role on the plastic behaviour of Mg alloy sheets. A numerical-experimental approach was adopted with the aim of designing equipment and test procedures, which can perform formability tests in warm conditions. Since finite element simulations need reliable and accurate data to model the forming process, the authors propose a methodology to evaluate the forming limit curve (FLC) according to both the temperature level and the (equivalent) strain rate value. Using the designed equipment and proposed approach, it is possible to: (i) force material failure in the central part of the specimen; (ii) define a constant temperature in the failure region; (iii) determine a constant equivalent strain rate in the failure region. Experimental tests in the present paper were carried out using a digital image correlation system, which is able to acquire strain maps during the entire forming process; experimental data allowed for both a validation of numerical results and the acquisition of important information about the effects of strain rate and temperature on the FLC of the AZ31 Mg alloy.