Abstract
An anomalous fine-grained structure of Mg-Zr alloy phase was observed in the annealed co-extrusion of Mg-0.5%Zr and Mg-1%Al powders.
The present experiment has been carried out to clarify this phenomenon. A cylindrical bimetal billet of pure Mg and Mg-0.5%Zr alloy was extruded at 400°C and the extruded bimetal was annealed at 350°∼550°C for 1, 3 and 9 hr. The grain size of Mg-Zr alloy phase near the interface to the pure Mg phase was measured and plotted in Figs. 2∼4 against the distance from the interface.
The fine-grained zone of about 0.3 mm in the Mg-Zr alloy phase adjacent to the pure Mg phase was observed in the as-extruded condition. Annealing the extruded bimetal at 550°C resulted in remarkable grain growth in the opposite side of this zone to the interface. The fine-grained zone, however, remained in the extent of ∼0.1 mm.
This fine-grained structure of Mg-Zr alloy phase seems attributable not to an ordinary deformation mechanism in the extrusion process of a single billet but to another mechanism caused by the co-extrusion with a softer material.
