Forgeability of AZ31B magnesium alloy in warm forging

To understand the forming behaviour of magnesium alloys, the upsetting test of Mg alloys at evaluated temperature was conducted. It is found that Mg alloys are brittle at temperatures below 200 ℃. When temperature is higher than 400 ℃, Mg alloy is not suitable for forging because of heavy oxidation. Mg alloy shows an excellent workability at temperatures from 250 to 400 ℃. Because in warm forging the flow stress decreases with increasing strain, which is so-called work softening, no appropriate material formulation is available for Mg alloys. For the evaluation of flow stress of Mg alloys in warm forging processes, a formula is derived by analyzing the stress data measured at various temperatures in upsetting test. It is demonstrated that the formula fits the flow stress obtained from experiment.