Achieving Ultrahigh Strength in Mg–1.2Y–1.2Ni (at.%) Alloy via Tailoring Extrusion Rate

Abstract

Mg–1.2Y–1.2Ni (at.%) alloy was extruded at 400 °C with an extrusion ratio of 16:1 and different rates from 1 to 6 mm/s. The effect of extrusion rate on microstructure and mechanical properties of the Mg–1.2Y–1.2Ni alloy was systematically investigated. With the increase of extrusion rate, the average recrystallized grain size of Mg–1.2Y–1.2Ni alloy and mean particle diameter of Mg₂Ni phase were increased, while the density of geometrically necessary dislocation and the intensity of the basal texture were decreased. When extrusion rate increases from 1 to 6 mm/s, the tensile yield strength (TYS) of as-extruded Mg–1.2Y–1.2Ni alloy decreases from 501 to 281 MPa, while the elongation to failure increases from 1.5% to 6.2%. The Mg–1.2Y–1.2Ni alloy extruded at 3 mm/s obtained TYS of 421 MPa, the ultimate tensile strength (UTS) of 440 MPa and elongation to failure of 2.6%, respectively, exhibiting comprehensive mechanical properties with relatively good plasticity and ultrahigh strength. The ultrahigh TYS of 501 and 421 MPa was mainly due to the strengthening from ultrafine recrystallized grains, high volume fraction long period stacking ordered (LPSO) phases and high density dislocations.