Consolidation of mechanically milled Al/Al₂O₃ and Al-8Zn/Al₂O₃ composite powders

In this work, the consolidation of composite powders of Al-xAl₂O₃ and Al-8Zn-xAl₂O₃ (where x=0, 1, 2, and 3 wt.%) has been studied. Al and Al-8wt.%Zn powders with a mean particle size of 5 μm were obtained by mechanical milling in a ball mill for 30 hours in hydrogen atmosphere. The milled powders were mixed with α-Al₂O₃ with a mean particle size of 0.4 μm in several percentages and consolidated by hot pressing. The effect of zinc addition and alumina content on density and hardness of consolidated samples was evaluated. It was found that zinc has a very strong effect on the sinterability of the composites, increasing the density of consolidated samples up to 97% of the theoretical density for Al-8Zn-xAl₂O₃ composites compared to a density of up to 75% reached in Al-xAl₂O₃ composites. Alumina particles increase the hardness of the Al-8Zn sample but decrease the density of the consolidated samples due to increased friction effects between particles.