Enhancing strength at elevated temperatures via dynamic high-density mobile dislocations in Mg alloys

• A new cast Mg-Y-Zn-Ho alloy was developed with an excellent elevated-temperature strength and ductility synergy. • The high-density dislocations are introduced through the interactions of dislocations and Ho atoms. • The TEM and molecular dynamics simulations show that Ho atoms pin dislocations and promote dislocation multiplication via the Frank-Read mechanism. • The high-density dislocations achieve a great enhancement of dislocation hardening, allowing the alloy to obtain the dual benefits of high strength and good ductility simultaneously at elevated temperatures. Dislocation strengthening, as one of the methods to simultaneously enhance the room temperature strength and ductility of alloys, does not achieve the desired strengthening and plasticity effect during elevated-temperature deformation. Here, we report a novel strategy to boost the dislocation multiplication and accumulation during deformation at elevated temperatures through dynamic strain aging (DSA). With the introduction of the rare-earth element Ho in Mg-Y-Zn alloy, Ho atoms diffuse toward dislocations during deformation at elevated temperatures, provoking the DSA effect, which increases the dislocation density significantly via the interactions of mobile dislocations and Ho atoms. The resulting alloy achieves a great enhancement of dislocation hardening and obtains the dual benefits of high strength and good ductility simultaneously at high homologous temperatures. The present work provides an effective strategy to enhancing the strength and ductility for elevated-temperature materials.