Study On The Microstructures And Mechanical Properties Of Mg-Gd-Y-Nd-Zr Alloys

Magnesium alloys are the lightest structural materials with high specific strength, good electric conduction, thermal conduction, damping capacity, electromagnetic shielding, formability, as well as easy recycled. It has great applying prospect on automobile, electro-communication, aviation, and military industry. However, its low strength become one of the limitations to extending application. As hotspot for scholars from both domestic and overseas, Mg-Gd-Y-Zr alloys keep high strength and excellent heat-resistance, due to large amount addition of heavy RE element like Gd. As a result, the alloys become not the very light as other commercial magnesium alloys. This study is targeted on decreasing the density of Mg-Gd-Y-Zr alloys without large decrease on the strength, through replacing part of Gd with Nd, studying on the phase composition and effects of Nd(Gd) on the solidified microstructures and the reverse extrusion deformation of Mg-Gd-Y-Nd-Zr alloys. In addition, the effects of heat treatment after extrusion are also studied in detail. The results obtained are summarized as follows:1) Phase composition of solidified microstructure in the Mg-Gd-Y-Nd-Zr alloys is mainly a-Mg and MgsRE; the form of second phase is primarily skeleton-like, precipitating discontinuously, as well as the granular and lamellar-like. The amount of the precipitate grows with the amount of Nd(Gd) additon enlarging;2) The Gd/Nd has a remarkble influence on the grain size of the Mg-Gd-Y-Nd-Zr alloys. Grain Size is small as the Gd/Nd stays a low value, while Gd/Nd get a high value, grain size tends to be a larger value;3) Dynamic recrystallization is observed in the extrusion deformation of Mg-Gd-Y-Nd-Zr alloy, as well as dynamic precipitation; the mainly phase are still a-Mg and MgsRE. When Gd/Nd tends to 1, new phase Mg4iNds appears as well as phase Mg24Ys;4) While the amount of Nd is high, the number of deformation band increases and the interlamellar spacing become shorter, and the number of dynamic precipitation decreases. The strength of the alloy is positive correlated to the amount of Nd. While the amount of Nd is low, intensifying effect is small. Same effect can be concluded from that of Gd addition;5) The strengthen effect of T5 heat treatment is influenced by the composition; Mg-6Gd-3Y-2Nd-0.6Zr alloy has the best mechanical properties after extrusion, of which Tensile strength is 390MPa, Yield strength is 350MPa and the Elongation is 1.8%. Mg-6Gd-3Y-2Nd-0.6Zr alloy's ageing strengthening effect are most obvious. After aging, the tensile strength increased to 435MPa, yielding strength to 359MPa and elongation to 5%, respectively.