Influence of Milling Atmosphere on the Controlled Formation of Ultrafine Dispersoids in Al-Based MMCs

Properties of compacts made from aluminium powder, milled under different atmospheres, were evaluated. The duration of all the milling processes was 10 h, although different atmospheres were tested: vacuum, confined ammonia, and vacuum combined with a short-time ammonia gas flow (5 min). Milled powders were consolidated by cold uniaxial pressing and vacuum sintering.The nature and content of the second phases change with the milling atmosphere, allowing the modification of the mechanical properties of the compacts. Results showed that hardness and tensile strength were highly dependent on the milling atmosphere. Milling carried out in vacuum with a short-time ammonia gas flow notably improved compacts' properties, as compared with 10 h vacuum milling. Hardness increased from 96 to 150 HB, and ultimate tensile strength rose from 247 to 476 MPa.