Extension of formability of the magnesium wrought alloy AZ31B-O at room temperature by pulse magnetic forming

摘要

For having the lowest density of all metal construction materials of 1.75 kg/dm3, magnesiumwrought alloys are outstanding lightweight materials. The low formability at room temperaturelimits the industrial use of magnesium AZ31B-O. In this paper the influence ofhigh strain rates was investigated with the aim to improve the formability of the alloyAZ31B-O at room temperature.The negative strain rate sensitivity of quasi-static strain rates causes an early loss of materialstability due to formation of local deformation zones on the work piece surface. Thisleads to a low formability in the forming state of plane strain, in which the forming limit(FLC) of magnesium alloy AZ31B-O has a critical minimum. For process illustration ofmulti-axial stress states - which appear in conventional forming processes - the pulsemagnetic forming process is used. To create plane strain formability a flat coil is used. Theapplied die is used to control the free formability. Hereby, a change of the maximum loadson the power transfer zone to areas of plane strain formability occurs.The results that have been achieved show that high strain rates at room temperature increasethe permitted loads of the material with plane strain formability significantly. Highspeed forming is linked to a rising strain rate sensitivity which increases the flow resistancein critical forming areas, in favor of a rising material stability. This fact is representedby equally reduction of the sheet thickness on the power transfer area. The homogeneouswork piece stress clearly increases the formability of AZ31B-O at room temperaturecompared to quasi-static forming process.