48 巻 (2007) 553 号 p. 105-109
For mashy-state forging of aluminum alloy using resistance heating, which was devised to eliminate the mashy-state billet handling indispensable to the current process, the influence of forging conditions upon the product condition was investigated by experimental gear forging using an A357 aluminum alloy prepared for mashy-state forging applications. Forging experiments were conducted by varying the operational variables of input electric energy and forging pressure, under the resistance heating conditions favorable to preventing sparks and realizing homogeneous billet heating. The product condition was examined by optical microstructure observation and hardness measurements, and the following findings were obtained. (1) The experimental mashy-state gear forging using resistance heating was successful under suitable operating conditions. (2) Rapid resistance heating prevented the growth of primary α grains. (3) For die-cavity filling, a lack of forging pressure was compensated with an increased input of electric energy to augment the liquid phase. (4) The eutectic phase and α phase tended to be dense in the periphery of the forged gear and near the electrodes, respectively. (5) The periphery of the forged gear that comes into contact with the metallic die was solution-conditioned by rapid cooling from the mashy state, and through natural aging, it became harder than the center.