Large hardening response mediated by room-temperature dynamic solute clustering behavior in a dilute Mg-Zn-Ca-Sn-Mn alloy

Regulating the solute atoms to form dense nano-sized precipitates is an essential strategy to enhance the strength of Mg alloys, wherein the maximum strength improvement is usually achieved by artificial aging at low temperatures (150-250 °C) for several to dozens of hours. In the present study, we found that a Mg-1.04Zn-0.52Ca-0.27Sn-0.18Mn (wt.%, ZXTM1100) alloy exhibits a substantial yield strength (YS) increment of ∼81 MPa after undergoing cyclic deformation (CD) at room temperature. Moreover, the impressive YS improvement only reduces the elongation to failure from ∼18% to ∼16%. To explore the strengthening mechanisms, the microstructure evolutions of cyclically deformed ZXTM1100 alloy have been systematically investigated by multi-length scale characterization techniques, including synchrotron X-ray diffraction, transmission electron microscopy (TEM), and correlative transmission electron microscopy and atom probe tomography (TEM-APT). It has been found that the strength increment mainly originates from the dynamic formation of a high density (∼5.7×10²⁴ m^-3) of multi-type solute clusters (e.g. Zn-Ca, Zn-Ca-Mn, and Zn-Zn), which can strengthen the alloy by ∼70 MPa. For the first time, such a high strengthening effect from the formation of solute clusters has been reported in a dilute Mg alloy. The accelerated solute clustering process can be rationalized when considering the supersaturated non-equilibrium vacancies produced by CD treatment. Our work not only demonstrates the pronounced cluster strengthening effect in a dilute Mg alloy, but also could provide new insights into the development of Mg alloys with high strength-ductility synergy.