Study On The Tensile Creep Anisotropy Of Deformed-state Mg-Mn-Ce Alloy

The creep anisotropy of wrought magnesium alloys caused by ubiquitous texture phenomenon will seriously affect their application.Various types of texture produced by hot deformation,i.e.,rolling,forging,extrusion,and so on,have different effects on the creep behaviors of magnesium alloys.The tensile creep behaviors of rolled and extruded Mg-Mn-Ce alloys were systematically studied in this paper.The creep mechanisms tested along different directions were detailed,and the creep anisotropy was analyzed.In addition,hot compression deformation on extruded Mg-0.9Mn-0.5Ce robs was carried out,creep behaviors with and without pre-deformation was compared.Thus,the effect of pre-strain on creep resistance was clarified.The creep behavior of hot rolled Mg-0.9Mn-1.5Ce alloy exhibited obvious anisotropy.The creep resistance ranked as TD≈RD>ND.Viscous gliding of dislocations dominated the creep process at 453 K in the TD and RD samples.Pyramidal slip started to activate and gradually controlled the creep behaviors because of the thermal activation at 473 K.As the temperature increased to 493 K,dislocation climb and pyramidal slip together controlled the creep.The dominant creep mechanisms had no change according to the stress exponent and the activation energy crept along the ND,but tensile twins and cross-slip were discovered.The different trends with temperature of creep mechanisms in each direction leads to enhanced creep anisotropy,and the strong interaction between pyramidal dislocations and dynamic precipitates during creep along TD/RD could enhance its creep resistance.Trace Ce element could increase the contribution of pyramidal slip during creep,improving the creep resistance of extruded Mg-Mn-Ce alloy.The creep resistance could be arranged as Mg-0.9Mn-0.5Ce（ED>TD）>Mg-0.9Mn（ED>TD）at 423 K.The creep behavior of Mg-0.9Mn alloy along ED was dominated by basal slip,cross-slip,twinning,dislocation climb and pyramidal slip.And the creep behavior along TD was dominated by basal slip,cross-slip and twinning.The creep mechanisms of Mg-0.9Mn-0.5Ce alloy along ED were basal slip,cross-slip and pyramidal slip.And the creep mechanisms along TD were mainly basal slip,twinning and dislocation climb.In addition,Ce element trended to segregate at grain boundareis and could promote the precipitation ofα-Mn,which were beneficial to enhance the creep resistance of Mg-0.9Mn-0.5Ce alloy.Furthermore,the great difference of twining and pyramidal slip during creep along ED and TD was the principal reason for the increase of creep anisotropy of extruded Mg-0.9Mn-0.5Ce alloy.Hot compression could improve the creep resistance of Mg-Mn-Ce alloy.The optimum creep resistance was obtained when deformation parameter was 623 K-10^-2 s^-1.The{101?2}tensile twinning was activated easily,and pyramidal slip became the main dislocation movement type at creep duration in C-ED samples.Besides,the creep fracture mode of the sample was ductile fracture.The addition of Ce promoted the initiation of non-basal slip during hot compression,resulting in complex dislocation movement and serious entanglement.In the further creep test,the activity and movement of dislocations were seriously hindered by preset entangled dislocation.In other words,the pyramidal slip was hardly activated,which further improved the creep resistance.