Underlying mechanisms of variation in yield asymmetry and strain hardening behavior of extruded pure Mg with Gd addition

Effects of Gd addition on the strain hardening behavior and yield asymmetry of pure Mg are investigated by subjecting extruded pure Mg,Mg–5Gd,and Mg–15Gd(all in wt%)to tension and compression tests along the extrusion direction(ED).As the amount of Gd added to pure Mg increases,the basal texture tilts toward the ED and the distribution of c-axes of grains becomes randomized.Under tension,the strain hardening rates of all the materials decrease until fracture.However,under compression,the strain hardening rate increases in the early stage of deformation in pure Mg and Mg–5Gd,whereas it continuously decreases in Mg–15Gd.Pure Mg exhibits considerably high tension-compression yield asymmetry,with a compressive yield strength(CYS)to tensile yield strength(TYS)ratio of 0.4.In contrast,Mg–5Gd exhibits excellent yield symmetry with CYS/TYS of 0.9 and Mg–15Gd exhibits reversed yield asymmetry with CYS/TYS of 1.2.Underlying mechanisms of these drastically different Gd-addition-induced deformation behaviors of the materials are discussed in terms of the crystallographic distribution of grains and the relative activation stresses of basal slip,prismatic slip,pyramidal slip,and{10–12}twinning under tension and compression.

Effect of Gd addition on mechanical and microstructural properties of Mg-xGd-2.6Nd-0.5Zn-0.5Zr cast alloys

The Mg-xGd-2.6Nd-0.5Zn-0.5Zr(x=0,3.0,4.5 and 6.0,wt.%)alloys were prepared by gravity casting and then T6 treatment.Microstructures of the alloy were observed using optical microscopy and scanning electron microscopy.Results show that the as-cast alloys contained network Mg3Gd phases,blocky and needle-like Mg12(Nd,Gd)phases.The a(Zr)particle inclusions in the a(Mg)matrix are also observed.Content of the secondary phases decreases as Gd content increases.Tensile test results show that the tensile and yield strengths of all the alloys increase as Gd content increases under the as-cast and T6 conditions,but the elongation exhibits the opposite trend.The blocky Mg12(Nd,Gd)phases appear and act as crack initiator and deteriorates the experimental alloys’ductility with the increase of Gd content,especially as Gd content increases to 6.0 wt.%,so the Mg-6.0Gd-2.6Nd-0.5Zn-0.5Zr alloy has the lowest elongation value compared to the other alloys studied.After T6 treatment,the Mg-4.5Gd-2.6Nd-0.5Zn-0.5Zr alloy exhibits the optimal mechanical properties both at room temperature and 250℃.

Effects of ECAP Extrusion on the Microstructure, Mechanical Properties and Biodegradability of Mg–2Zn–xGd–0.5Zr Alloys

Effects of equal channel angular pressing(ECAP)extrusion on the microstructure,mechanical properties and biodegradability of Mg–2Zn–xGd–0.5Zr(x=0,0.5,1,2 wt%)alloys were studied in this work.Microstructure analysis,tensile test at ambient temperature,immersion test and electrochemical test in Hank’s solution were carried out.The results showed that Gd could further enhance the grain refinement during the ECAP extrusion.Both Gd addition and ECAP extrusion could improve the mechanical properties of the alloys,and the extrusion played the dominant role.Minor addition of Gd(0.5–1 wt%)could obviously enhance the corrosion resistance of the alloys.To some extent,ECAP extrusion improved the corrosion resistance of the alloys due to the change of second phases distribution and the refinement of grains.Further increase in extrusion pass was detrimental to the improvement of the corrosion resistance as a result of increment of the grain boundaries.