Effect Of Alloying Element Er On The Structure And Mechanical Properties Of Mg-4Y-3Nd-0.5Zr Alloy

Mg-RE alloys integrate the best performance in the casting of magnesium alloys. Mg-Y-Nd based alloys have excellent properties. Rare earth element Er has the hcp structure and the maximum solubility in the magnesium is 32.7 mass%. Er can more easily dissolved into the magnesium than Y and Nd. Therefore, Er element can be considered as the fourth group added into the Mg-Y- Nd alloy. The influence of Er element on the matrix structure and properties was studied.By adding Er to Mg-4Y-3Nd-0.5Zr alloy, new Mg-4Y-3Nd-xEr-0.5Zr(x=0,1,2,4)alloys were developed under a protective atmosphere of SF6+Ar mixed gas by casting technology. The microstructures and mechanical properties of as-cast and as-T6 (artificial aging after solution treatment) alloys have been investigated by means of metallographic analysis, Energy-Dispersive X-Ray Spectroscopy, X-ray diffraction (XRD), and scanning electron microscope (SEM) techniques. The main results can be summarized as follows:The microstructures of as-cast Mg-4Y-3Nd-xEr-0.5Zr(x=0,1,2,4)alloys were identified by the mainα-Mg phase and small quantity of granular intermetallic compound Mg24Y5 and reticular intermetallic compound Mg41Nd5. With the Er concentration increased gradually, the maximum solubility of Y and Nd decreased and the quantity of second phases Mg24Y5 and Mg41Nd5 increased.After solution treatment at 535℃for 16h, the interdendritic structure of the specimens was eliminated , but the dispersed granules still existed. With Er content increased, the grain sizes of the alloys changed little but the quantity of second phases increased. The hardness arrived at the peak quickly after aging at 250℃. The straight and lamella Mg24Y5 phases were observed in the alloys, and there was intermetallic compound Mg24Y5 . This was the main reason for precipitation strengthening. There was no Mg24Er5 phase in the matrix, the granules were intermetallic compounds Mg24Y5 and Mg41Nd5. It indicated that solid solution strengthening was the mainly effect of Er while precipitation strengthening was the main effect of Y.Tensile test showed that: the strength of the as-cast alloy increased first, and decreased while the Er content increased. The tensile strength didn't show a regular trend after aging treatment. The as-cast and peak-aging tensile strength arrived at maximum of 151Mpa and 247 Mpa respectively when the Er content at 2 mass%.The fracture analysis showed that: the fracture mode of Mg-4Y-3Nd-xEr-0.5Zr (x = 0, 1, 2, 4) alloys is quasi-cleavage fracture. The peak aging state of the fracture mode of the alloys is intergranular fracture, cleavage fracture, cleavage fracture and intergranular fracture, and quasi-cleavage fracture.