High temperature behavior of nanostructured Al powders obtained by mechanical alloying under NH3 flow

Aluminium powder was mechanically alloyed under ammonia gas flow for different times (1-5 h) in order to produce a second-phase reinforcement, mainly by aluminium nitride (AlN). After milling, powders were consolidated by cold uniaxial pressing and vacuum sintering. A small amount of copper powder was added to the Al milled powder to improve its sintering behavior. Hardness and indirect tensile test were carried out at room and high temperature to evaluate the mechanical properties evolution. Results showed an remarkable hardness increase with the second phases content, even at high temperature (up to 229 HB at 400 ºC). However, the high content of second phases of ceramic nature decreases the ductility, resulting in low values of tensile strength (lower than 160 MPa).