Sintering Behavior of Nanocrystalline Al6063 Powders Prepared by High-Energy Mechanical Milling

Abstract

Nanocrystalline Al6063 powders were synthesized by high-energy mechanical milling of gas-atomized powders for 22.5 h. The powders were uniaxially compacted at various compaction pressures ranging 200–1325 MPa and then were sintered at temperatures between 550 and 650 °C for 1 h. The densification and microstructural evolutions during both solid phase sintering and supersolidus liquid phase sintering are studied. Ultrafine-grained (UFG) Al alloy compacts show superior sinterability compared with coarse-grained (CG) compacts due to the higher defect density and larger specific surface area of the mechanically-milled powders. The densification parameter and hardness of both CG and UFG Al6063 compacts enhances as the compaction pressure increases. Nevertheless, applying high compaction pressures has an adverse effect on the sintered density and results in the swelling of compacts. The results point out an optimum sintering temperature at ~600 °C for achieving the highest sintered density and hardness with minimal grain coarsening and slumping.