Abstract
Some mechanical properties at room and elevated temperatures of extrusions made of jet-atomized magnesium-1wt% aluminium alloy powder, magnesium-0.6wt% zirconium alloy powder and simultaneous extrusion of 50/50 mixture of these two powders have been investigated. The powder-extrusions, in comparison with cast-billet extrusion, have finer grains and higher hardness than that of the latter in both as-extruded and annealed states. They also have at all testing temperatures higher ultimate tensile strength, yield strength and especially exhibit a higher creep resistance at 350-450°C but lower elongation. This seems to be very much concerned with the amount of oxide dispersed which is also attributable to poor ductility of the powder-extrusions. The metallographic observation of cavities in creep-ruptured specimens shows that the cavities originate preferentially at the longitudinal grain boundaries, which were formerly the surface of the powders and where oxide particles exist, rather than at the transverse grain boundaries. The cavities grow toward the transverse direction and continuation of cavities results in fracture of specimens. Some consideration of the interaction between dislocations and oxide particles have also been made.
