Tensile behaviour of mechanically alloyed precipitation hardened aluminium alloy IN 9021

Abstract

The room temperature tensile behaviour of the mechanically alloyed aluminium alloy IN 9021 was studied. Precipitation hardening increases the tensile strength from 485 MN m⁻² in the as-extruded condition to 620 MN m⁻². Mechanical alloying produces a fine grain size, a high dislocation density, and a dispersion of ultrafine Al₂O₃ and Al₄C₃particles. During annealing at temperatures up to the solidus, recovery and continuous recrystallization take place, but there is no significant grain growth. High-temperature tensile testing showed that the precipitation hardened alloy loses strength more rapidly than the as-extruded alloy, and is the weaker at temperatures > 180°C. The as-extruded alloy has a maximum strain rate sensitivity of 0·13 at 300°C. This lack of superplasticity, in spite of the fine grain size, is believed to be due to the high hardness of the pinning oxide and carbide particles, which tend to prevent easy slip and grain boundary sliding.

MST/423