Effect Of Rare Earth On AZ Series Magnesium Alloys

The study of Magnesium alloys have taken more and more attention, especially the strengthen and elongate of Mg alloys.The experiment material of this paper is AZ61 and AZ91 magnesium with addition of rare earth(RE) Ce, Nd and Y separately. A part of the alloys were extruded with the extrusion ratio of 18 and then made specimens together with the as-cast alloys. Through investigation of the microstructures and tests of the mechanical properties, the strengthen mechanism of RE and hot-extrude process was discussed, which is helpful for further study.The results showed that: compared with magnesium alloys, the RE-Mg alloys have better high-temperature mechanical properties, while that of the ambient-temperature almost the same. The addition of RE also refined the grain of the Mg alloys. In addition, the optimal content differs with different RE. For as-cast AZ61 and AZ91 alloys, the optimal content of Ce is 1.5%, at where they can reach the maximal ultimate tensile strength σ_b, yield strength σ_0.2 and elongation to failure 5;while the best content for Nd is 0.5%, at where the high-temperature mechanical properties are the best. For extruded alloys, with the content of 0.5% Ce and Nd separately, they have the maximal high-temperature strength and elongation;while the optimal content of Y is 1.5%. After hot-extrusion, the mechanical properties of RE-Mg alloys promote greatly. At ambient-temperature, the σ_b of extruded AZ61+1.0%Nd alloy can reach 292.6MPa, 61.9% higher than the as-cast alloys of the same component;atl50°C, the σ_b of extruded AZ61+1.0%Ce alloy can reach 289.1 MPa, 76.4% higher than the as-cast alloys of the same component. Compared with as-cast alloys, the strength hot-extruded alloys are lOOMPa higher approximately, and the tendencies of that are more ordered: with the rising of the temperature, the elongation rises and the strength fall.It is considered that the addition of RE can refine the grain and purify the grain boundary;the extrusion of alloys can uniform the microstructure and refine the grain, all these can improve the mechanical properties of magnesium alloys.