Effect of consolidation temperature on mechanical properties of rapidly solidified Al–7Mg–1 Zr alloy

The mechanical properties achieved via the extrusion of non-degassed billets prepared from an inert gas atomised powder of nominal composition Al–7Mg–lZr are reported. The alloy was extruded over the temperature range 350–550°C and the tensile mechanical properties and plane strain fracture toughness were evaluated. It was found that the yield strength remained fairly constant over the entire temperature range, with only a small decrease in strength observed at the highest extrusion temperature. The strength could be related to microstructure using standard models for solid solution, dispersoid, and substructural strengthening mechanisms, and the last was found to make the greatest contribution. The sensitivity of strength to subgrain size was found to be nearly three times higher than that for pure Al. The optimum combination of strength and fracture toughness was obtained for extrusion at 500°C (yield strength 400 MN m−2; T–L KIv 21 MN m−3; elongation 20%). The poor values of Klv obtained at other temperatures were attributed to coarse dispersoids (highest extrusion temperature), undeformed powder particles (lowest extrusion temperature), and inhomogeneous dispersoid distributions (intermediate temperatures). It is concluded that extrusion process control plays an important role in determining the mechanical properties of consolidated rapidly solidified powders. Considering the excellent ductility and toughness obtained, vacuum degassing before extrusion may not be essential in the processing of inert gas atomised powders of a non heat treatable composition.