Extruded high-strength solid materials based on magnesium with zinc, yttrium, and cerium additives

Magnesium (the lightest structural material) is suitable for manufacturing movable parts of vehicles and finds wide application in car and aerospace engineering. Magnesium alloys produced by conventional casting have defects and large-sized grains and exhibit undesirable mechanical properties. The desirable properties of magnesium alloys can be achieved by improving their microstructure. This paper reports on the results of investigations of high-strength products (8-50 mm in diameter) prepared by extrusion from rapidly solidified ribbons of the Mg-6Zn-1.5Y-0.5Ce alloy (hereafter, numbers in the compositions indicate the elemental content in wt %). The tensile strengths of the products are equal to 450-520 MPa, and their elongation (E, %) is limited. The microstructure of the materials at each stage of treatment is examined using optical microscopy or scanning electron microscopy with energy-dispersive X-ray analysis and X-ray diffraction. It is demonstrated that Mg-Zn-Y-Ce alloys with a fine-grained structure can be prepared by both conventional casting and rapid solidification. The mean sizes of magnesium solid-solution grains and supersaturated magnesium solid-solution grains are equal to 45 and 5 µm for alloys produced by casting and rapid solidification, respectively. The formation of a fine-grained structure is predominantly associated with the remelting of solidified dendrites. In this process, cerium plays a decisive role. The theoretically expected tensile yield strength of the Mg-6Zn-1.5Y-0.5Ce high-strength solid materials produced by extrusion should be higher for materials with a fine-grained structure. It is shown that the discrepancy between the theoretical and experimental results is caused by the extrusion defects. The conclusion is drawn that the strength of the materials extruded from rapidly solidified ribbons depends on their microstructure and extrusion conditions.[PUBLICATION ABSTRACT]