Fig. 1 shows the isothermal densifi

Fig. 1 shows the isothermal densification behavior of compacts of as-received and classified powders at different temperature. As observed, the compacts of classified powder can achieve almost full density (>99% theoretical density) for all sintering temperatures but those of the as-received powder cannot. Fig. 2 shows the evaluation of the activation energy of isothermal sintering of the compacts of the as-received and classified powders. The evaluated values are420 and 452 kJ mol−1 for classified and as-received powder compacts, respectively, which are close to the grain boundary diffusion of the aluminum ion [5]. Fig. 3 shows the particle size distributions of as-received and classified powders.