Experimental study on direct-reverse quick gas blow forming of magnesium alloy sheet

High strain rate gas blow forming tests were performed using two types of reverse preform dies, and the results showed that the forming effect of inner and outer circle arc preform die was better than that of semicircle preform die. The surface and microstructure of formed parts appeared hardly defect and the reverse forming time was shortened to 10s. Direct-reverse free bulging tests for hemisphere part with the above perform dies were conducted to investigate the direct-reverse forming behaviour. Compared to unidirectional free bulging, the direct-reverse forming improved significantly formability of AZ31 magnesium alloy sheet, and increased the height to diameter ratio of hemisphere part from 0.344 to 0.522 and the uniformity of thickness distribution from 19.4% to 32.3% for semicircle perform die and even to 45.5% for inner and outer concave circle arc perform die. The undamaged hemisphere part with height to diameter ratio of 0.522 was formed successfully at 400°C within 300 s.