Unraveling the individual effect of yttrium and neodymium on the precipitate-free zone development and the dislocation creep mechanism of Mg-Y-Nd alloy

The individual effects of Y and Nd elements on the precipitate-free zone (PFZ) development and the dislocation creep mechanism of a Mg-4Y-3.5Nd alloy were investigated using tensile creep loading at 553 K. Some of the samples were treated with a solid solution (WNS) and others were treated by peak aging (WNA). Before creep, no precipitates were found in the WNS sample, whereas both lamellar binary phases and platelet ternary phases were found in the WNA sample and PFZs were already formed. After creep, cross slip and pyramidal  slip were detected as the dominant creep mechanisms in the WNS sample under all stress regimes. Only cross slip dominated the creep of the WNA sample under low-stress regimes, whereas pyramidal slip also became dominant under high-stress regimes. Dynamic precipitation of ternary phases was observed, and PFZs gradually developed in the WNS sample under all stress regimes. Ternary phases persisted in the WNA sample under all stress regimes, but the dissolution of binary phases and widening of PFZs were significant under high-stress regimes. Consequently, greater creep resistance was achieved in the WNA sample under low-stress regimes but in the WNS sample under high-stress regimes. Compared to Mg-7.5Y and Mg-3.5Nd binary alloys, the synchronous addition of Y and Nd to form a Mg-4Y-3.5Nd alloy diversified the slip types. The Y element reduced the widening rate of PFZs, but it could not thoroughly prohibit the formation of PFZs. The Nd element accelerated both static and dynamic precipitation, but it also triggered the rapid widening of PFZs.