Enhanced strength and ductility of Mg-Gd-Y-Zr alloys by secondary extrusion

The Mg-12Gd-3Y-0.6Zr(GW123,wt.%)alloy was prepared by cast,and thermo-mechanically treated by single and secondary hot extrusion techniques.The microstructure,texture and mechanical properties of the extruded alloy were investigated.The results show that in different treated conditions the microstructure is mainly composed ofα-Mg solid solution and second phases of Mg_(3)Y_(3)Gd_(2) and Mg_(5)(GdY)precipitates.The best mechanical properties are achieved in the secondary extruded alloy after ageing,with the ultimate tensile strength(UTS),tensile yield strength(TYS)and elongation(ɛ)being 446 MPa,350 MPa and 10.2%at room temperature.A weak texture aligned with〈101¯0〉||ED(extrusion direction)component and spread from〈101¯0〉to〈112¯0〉poles was obtained in secondary extrusion,which is caused by the occurrence of dynamic recrystallization(DRX)in shear bands for texture randomization.The fracture modes in extruded GW123 alloy are mixed pattern of transgranular and intergranular fracture,as well as cleavage fracture.The strengthening mechanisms were quantitatively analysed from the different aspects using the measured microstructural parameters.The grain boundaries and solid solution strengthening were the main contributors to the high tensile strength of the GW123 alloy.

Investigation of magnetic inhibition effect on ion acceleration at high laser intensities

The irradiation of a target with high laser intensity can lead to self-generation of an intense magnetic field(B-field)on the target surface.It has therefore been suggested that the sheath-driven acceleration of high-energy protons would be significantly hampered by the magnetization effect of this self-generated B-field at high enough laser intensities.In this paper,particle-in-cell simulations are used to study this magnetization effect on sheath-driven proton acceleration.It is shown that the inhibitory effect of the B-field on ion acceleration is not as significant as previously thought.Moreover,it is shown that the magnetization effect plays a relatively limited role in high-energy proton acceleration,even at high laser intensities when the mutual coupling and competition between self-generated electric(E-)and B-fields are considered in a realistic sheath acceleration scenario.A theoretical model including the v 3 B force is presented and confirms that the rate of reduction in proton energy depends on the strength ratio between B-and E-fields rather than on the strength of the B-field alone,and that only a small percentage of the proton energy is affected by the self-generated B-field.Finally,it is shown that the degraded scaling of proton energy at high laser intensities can be explained by the decrease in acceleration time caused by the increased sheath fields at high laser intensities rather than by the magnetic inhibitory effect,because of the longer growth time scale of the latter.This understanding of the magnetization effect may pave the way to the generation of high-energy protons by sheath-driven acceleration at high laser intensities.