Nanoscale precipitates with quasicrystal domains enhanced strength-ductility synergy in a Mg–6Zn–4Al–1Sn–0.5Mn alloy

Precipitation strengthening is one of the significant strengthening mechanisms for metallic alloys owing to its excellent strengthening effect. Here, we effectively introduce homogenous nanosized precipitates into a Mg–6Zn–4Al–1Sn-0.5Mn (wt.%) alloy via extrusion and double aging to enhance strength-ductility synergy. The yield strength, ultimate tensile strength, and total elongation of the Mg alloy are 303.1 ± 15.8 MPa, 392.5 ± 3.9 MPa, and 21.1 ± 2.4%, respectively. Using transmission electron microscopy and atomic level high angle annual dark field-scanning TEM, in addition to the icosahedral quasicrystalline (IQC) particles at the grain boundary, we find that there are two kinds of nanoprecipitates in the matrix. The majority of nanoprecipitates are cuboid IQC phases with nanodomains parallel to the basal plane of the Mg matrix, while the minority of nanoprecipitates are rod-like β1′ phases containing IQC clusters vertical to the basal plane. These homogenous nanoscale precipitates and grain refinement contribute 50.5% and 30.2% of the yield strength. This work sheds new light on understanding the nanoscale IQC precipitate strengthening mechanisms of magnesium alloys and provides a novel method to fabricate alloys with superior mechanical properties.