Precipitation microstructure and their strengthening effects of an Mg-2.8Nd-0.6Zn-0.4Zr alloy with a 0.2wt.% Y addition

A micro-alloy addition of Y (0.2wt.%) produced a significant improvement in the tensile yield strength of an Mg-2.8Nd-0.6Zn-0.4Zr (wt.%) alloy at 200°C, with a 28% increase from 143MPa to 183MPa. APT characterisation confirmed that small solute clusters in a high number density were present in the as-quenched sample. TEM examinations revealed that β-type precipitates habiting on prism 1 1 2 0 planes were dominant in the sample after aged for 14h at 200°C, and they co-existed with γ-type precipitates on the basal plane of Mg matrix. The precipitation sequence of β-type precipitates is solute clusters→β'→β'→β₁ before the peak hardness. There was significant clustering of solutes in the Y-containing alloy, but Y did not clearly partition into clusters or precipitates and remained in the Mg matrix. β', β' and β₁ were measured with stoichiometric Mg₉(Nd,Zn), Mg₄(Nd,Zn) and Mg₂(Nd,Zn), respectively.