The Effect Of Nd (Y) On Microstructure And Mechanical Properties Of Mg-Zn Alloys

Wrought magnesium is noted to have a higher strength and ductility than cast magnesium. To research the good properties for magnesium alloys contained RE, in the present research Nd and Y respectively is odded to the Mg-5wt%Zn base alloys to produce as-cast and as-extruded(hot-extruded, extruded ratio is 17.5:1) alloys with different composition. This paper investigates the effect of RE elements and processing methods on microstructure and mechanical properties and discusses the strengthening mechanism.The results show that Nd addition on Mg-5wt%Zn magnesium alloy refine the grain; especially, when content of Nd is 3wt% the grains are the most finest. When Mg-5wt%Zn-(1-5)wt%Nd alloy is extruded at 330±10℃, the grain refined obviously. Comparing to as-cast alloy of the same composition, the size of grains of hot-extruded alloy is finer, with the increase of percentage of Nd, and the longitudinal linear of microstructure is more obvious. Moreover, when hot-extruded Mg-5wt%Zn magnesium alloy, content of Nd is 3wt%, the ultimate tensile strength is 330.1MPa; and yield strength is 294.8MPa; the elongation is 9.84% at room temperature. The ultimate tensile strength is 248.4MPa; and yield strength is 203.4MPa; the elongation is 34.16% at 150℃. The ultimate tensile strength is 219.4MPa; and yield strength is 191.5MPa; the elongation is 42.6% at 200℃. The research on the microstructure and tensile properties of as-extruded Mg-5wt%Zn-(1-5)wt%Nd alloys reveals the alloys are not sensitive to aging treatment and the microstructure and the tensile properties have no obviously change. So the heat treatment is not necessary for this series of magnesium alloy. In addition, the effect of Nd and Y on the Mg-5wt%Zn alloy is almost the same.Discussion shows that RE addition and extruded treatment have huge effects on tensile properties of Mg-5wt%Zn alloy. They can refine grain and purify the grain boundary, which can improve the strength and ductility of alloys. Fracture surface analyses reveal that at low temperature, cleavage surface and tearing ridge of as-cast alloy, which was taken as typical brittle fracture features, could be seen on fracture surfaces. With increasing test temperature, brittle features decreased, while ductile ones increased. At elevated temperatures, cleavage surface was replaced by large amount of homogeneously distributed dimples.