Simultaneous application of various rare earth elements in casting magnesium alloy

1. Application of rare earth Y, CE in AZ91 cast magnesium alloy

The results show that the combined effect of Y, CE and Si on the as cast microstructure of AZ91 magnesium alloy can significantly refine the matrix grains of α – Mg phase, reduce the number of β – Mg17Al12 phase, distribute in spherical mass, refine Mg2Si phase and promote the dispersion of Mg2Si phase in short rod shape. When rare earth Y and CE are added to magnesium alloy at the same time, acicular al11ce3 phase and massive al2y phase are formed, and the matrix grains of α – Mg phase are significantly refined by the composite action of two alloying elements, so that the amount of β – Mg17Al12 phase precipitated along the grain boundary is reduced, and the distribution tends to be more dispersive. This trend is more obvious with the increase of Y and CE. In addition to al11ce3 and al2y phases, the Chinese character Mg2Si phase formed by Si and Mg is distributed in the grain boundary, and promotes the refinement of the magnesium alloy structure. With the increase of rare earth elements, the phase of Mg2Si can be refined obviously, and the morphology of Mg2Si can be changed to make its distribution more dispersive.

After the addition of rare earth and yttrium to AZ91 cast magnesium alloy, the high melting point aluminum rare earth compound and aluminum yttrium compound first crystallized and precipitated during the solidification process, and became the nucleation center of the matrix phase, or were pushed to the front of primary α phase crystallization, which hindered the growth of α phase and refined the as cast structure. On the other hand, the formation of these two compounds also consumes a large amount of alloy element aluminum, weakens the effect of age hardening, and delays the emergence of peak age.

2. Application of rare earth Y and CE in AM50 casting magnesium alloy

It can be seen from the study of the effect of the combined action of rare earth Y, CE and Si on the as cast and solution treated structure of AM50 casting magnesium alloy that the combined action of rare earth Y, CE and Si can refine the structure of the alloy significantly and change the phase appearance of Mg2Si, making it change from a typical Chinese character shape to a short rod shape, dispersing in the grain boundary, but the Chinese character shape of Mg2Si still exists. Solution treatment can completely dissolve β – Mg17Al12 phase and make the size of al2y and al11ce3 compounds smaller. The size and distribution of Mg2Si phase are not affected by solution treatment.

3. Application of rare earth Y, CE in ZM5 cast magnesium alloy

The microstructure and phase composition of mg-8.5al-0.5zn (ZM5) cast magnesium alloy with rare earth elements y, Nd and Ti intermediate alloy were analyzed by metallographic microscope and X-ray diffractometer. The mechanical properties of the alloy at room temperature were tested. The results show that a new mg re phase mGy, mg12nd appears in ZM5 magnesium alloy with y, Nd, and a new phase ti2mg3al18 appears in the intermediate alloy with y, Nd and Ti. The tensile properties, hardness and microstructure of ZM5 magnesium alloy with re y and nd are better than those of ZM5 magnesium alloy, while the properties of magnesium alloy with RE and Ti are better than those of alloy with y or nd alone. The alloy after solution treatment was studied by metallographic microscope and X-ray diffractometer. It is found that rare earth elements are mainly distributed in the grain boundary, which can stabilize the grain boundary and refine the grain.

4. Flame retardant effect of rare earth Y and Ce on cast magnesium alloy

Y. Due to the selective oxidation of rare earth elements such as CE, at high temperature, Mg-Y or mg-y-ce first adds Y2O3 film to the surface of magnesium alloy, which can prevent further oxidation and combustion of the alloy. If y and CE are added separately, the flame retardant effect is not obvious; if the two elements are added at the same time, the effect is very different. Mg-y-ce alloy can be melted at 1173K without any protection.

5. Application of rare earth Y, Nd in ZK60 cast magnesium alloy

The hot rolling and heat treatment of mg Zn Zr system ZK60 cast magnesium alloy with rare earth elements y and nd were carried out. The room temperature tensile properties of ZK60 alloy and zk60re alloy were tested. The microstructure of the alloy in different states was observed by means of metallographic microscope, scanning electron microscope and X-ray diffraction. The results show that the rare earth elements y and nd can refine the as cast structure of ZK60 alloy and greatly improve its room temperature fracture strength. The addition of Y and CE can refine the as cast structure of ZK60 and improve the mechanical properties of the alloy. The room temperature tensile strength of the alloy increased by 12.6%, while the elongation of the alloy increased by CE. Rare earth elements CE and Y refine the as cast structure of ZK60 alloy, and refine the recrystallized grains after extrusion. In contrast, y has a stronger thinning effect.

6. Application of rare earth Y, CE, La in casting magnesium alloy

Adding y and mixed rare earth (mm) containing Ce and La, massive al2y was formed in die casting AZ91 + 1% y magnesium alloy, and rod-shaped AL4 (CE, LA) compound was formed in AZ91 + 1% mm alloy. Both of them have high thermal stability and high microhardness, thus strengthening the alloy. The critical stress σ C required for dislocations to break free of Y and CE atoms in AZ91 + 1% Y and AZ91 + 1% mm alloys is calculated. The results show that the σ C of AZ91 + 1% y alloy is larger than that of AZ91 + 1% mm alloy at the same temperature, which is one of the reasons why AZ91 + 1% y alloy has higher strength than AZ91 + 1% mm alloy. The results of high temperature tensile test show that the tensile strength and yield strength of AZ91 + 1% Y and AZ91 + 1% mM magnesium alloy decrease with the increase of temperature, and the tensile strength and yield strength of AZ91 + 1% y alloy are higher than those of AZ91 + 1% mm alloy.

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