High-strength Mg-6Zn-1Y-1Ca (wt%) alloy containing quasicrystalline I-phase processed by a powder metallurgy route

Abstract

A high-strength Mg-6Zn-1Y-1Ca (wt%) alloy has been processed by a powder metallurgy route. Rapidly solidified powders with a particle size below 100 µm were used as a way for preventing formation of ternary MgZnCa compounds during subsequent extrusion at 250 °C. The microstructure of the extruded alloy consists of an ultrafine-grain magnesium matrix, with an average grain size of 444 nm, embedding a high volume fraction of fine I-phase particles aligned along the extrusion direction. The alloy combines an excellent ductility (14% of elongation to failure) with a high strength (ultimate strength of 469 MPa and yield stress of 461 MPa) at room temperature, mainly due to grain size refinement (around 70% of the yield stress). The strength is kept high up to 150 °C (yield stress of 279 MPa). Above this temperature, the mechanical strength falls to very low values but the ability to deform plastically is considerably enhanced, exhibiting superplastic behaviour from 200 to 350 °C, with a maximum elongation of 477% at 350 °C.