Novel hexagonal structure of ultra-high strength magnesium-based alloys

Abstract

A magnesium (Mg) solid solution with a novel long periodic hexagonal structure was formed for a Mg97Zn1Y2 (at%) alloy in a rod form prepared by extrusion of atomized powders at 573 K as well as in a melt-spun ribbon form. The novel structure of the rod alloy had an ABACAB-type six layered packing with lattice parameters of a = 0.322 nm and c = 3 × 0.521 nm. The Mg phase in the extruded rod alloy had fine grain sizes of 100 to 150 nm and included cubic Mg24Y5 particles with a size of about 10 nm at volume fractions below 10%. The density (ρ) was 1.84Mg/m3. The tensile yield strength (σy) and elongation of the rod alloy were 610 MPa and 5%, respectively, and the specific strength defined by the ratio of σy to ρ was 330 MPa/(Mg/m3), being the highest among all metallic alloys. The σy is 2.7 to 8 times higher than those for conventional high-strength Mg-based alloys. The excellent mechanical properties are due to the combination of fine grain size, new long periodic hexagonal solid solution, homogeneous dispersion of fine Mg24Y5 particles inside the nano-grains and the absence of the second precipitates along the grain boundary. The new Mg-based alloy is promising for future uses in many fields.