Cerium For Mg - Gd - Y - Nd - Zr Alloy Microstructure And Properties Of Influence

Mg-Gd-Y-Zr alloy has excellent properties at room temperature and elevated temperature.,which has broad application prospect in the field of aerospace. The effects of rare earth Ce addition on the microstructures and properties of Mg-5.5Gd-4.5Y-Nd-Zr alloy were investigated by optical microscopy (OM), vickers hardness test, X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile tests and thermal simulation experiments. Main conclusions were listed in the following:(1) The effect of rare earth element Ce on cast structure of Mg-5.5Gd-4.5Y-Nd-Zr alloy was investigated. The as-cast grains of Mg-5.5Gd-4.5Y-Nd-Zr alloy were refined by addition of Ce. The grains of the alloys became finer with increasing Ce content in the range of0-0.2%significantly. The average grain size of as-cast alloy was decreased from68.7um to55μm. But the grains were not to be refined by further increasing of Ce content. The refinement mechanism was showed as follows:Ce addition increased the nuclei as a result of increasing the melt undercooling at solid-liquid frontier in solidification process.(2) The meshed non-equilibrium eutectic which was distributed on the grain boundaries was observed in the cast alloy, and it was composed of a-Mg and Mg5.05Gd. After solution treatment, the non-equilibrium eutectic integrated into the matrix, leaving a kind of square massive particle which the chemical composition was Mg2Gd.(3) The distribution and existence form of Ce in Mg-5.5Gd-4.5Y-Nd-Zr alloy were studied, which was in form of ellipsoidal Mg12Ce particles near the grain boundary mainly. Only a small amount of Ce was soluted into the matrix.(4) The chemical composition of alloys were optimized, and the optimum composition was Mg-5.5Gd-4.5Y-Nd-0.2Ce-Zr. The ultimate tensile strengths at extruded-T5state were402MPa and232MPa at room temperature and300℃, which were increased46MPa and30MPa compared with Mg-5.5Gd-4.5Y-Nd-Zr alloy respectively. The improvement of room temperature strength could be attributed to β’phase precipitation which was promoted by Ce addition. The high temperature strength improvement could be attributed to the increasing in volume fraction of β’ precipitate and the Mg12Ce particles which had a high thermal stability.(5) The hot-compression of Mg-5.5Gd-4.5Y-Nd-xCe-Zr (x=0,0.2wt.%) alloy at temperatures of375℃～525℃and strain rates of0.01s-1、0.1s-1、1s-1was investigated. The apparent activation energy of the two alloys at425℃～525℃were191KJ/mol and212KJ/mol, respectively. Addition of Ce increased the recrystallization volume fraction and decreased the recrystallization grain size because the ellipsoidal Mg12Ce particles occurring during solution could accelerate recrystallization by the mechanism of particle stimulated nucleation (PSN).