Novel forging technology of a magnesium alloy impeller with twisted blades of micro-thickness

In this work, a novel forging technology has been developed to produce a magnesium alloy impeller with twisted blades of micro-thickness used in a fuel cell system. Due to the very complicated blades of the impeller, a specially designed split die was adopted for successful forging of the impeller. In this split die-set, the coherence of reinforcement ring and split dies is induced by forging pressure which increases with increasing forging load. Both the reinforcement ring and the split dies have appropriate tapers so that during the forging process they are consolidated to allow no gap between the split dies and are separated easily after forging. This novel technology can provide the near net-shaped impeller without the burr generation when split dies are used. Based on the newly developed technology, the impeller forging experiments were carried out using magnesium alloy AZ31 which had been microstructurally refined through equal channel angular pressing (ECAP). The tensile and thermal stability tests were carried out under various levels of temperature and strain rate to find optimum processing conditions for precision impeller forging. Finally, the changes in microstructure and microhardness at the various positions of the forged impeller were investigated to compare with those of the initial billet. It has thus been shown that the proposed new method is effective to achieve precision forging of a magnesium alloy with high precision. (c) 2008 CIRP.