Rare Earth Elements (ce, Y) On The Grain Size Of The High-purity Mg-3al Explore Its Mechanism

Among various types of grain refining methods of Mg-Al alloys, carbon inoculation is one of the most promising and the best applied potential refinement, but the details of the refinement mechanism are not very complete. Recently, the method of adding rare earth elements into Mg-Al alloys was becoming a hot studying direction.However, in the process of inquiring the mechanism of the refinement, there were some relative contradictory understanding.In order to avoid the influence of impurity elements on the grain, high purity Mg-3A1 alloy was used for the study in this article. High purity Mg-3 Al alloy was first inoculated by rare earth elements (Ce, Y), grain coarsing happened. Then on this basis, C2Cl6 was added into the melt. The influence on the grain size was investigated. The mechanism of rare earth elements (Ce, Y) on the grain size of high purity Mg-3A1 alloy and the mechanism of rare earth elements on the carbon inoculation were investigated together.For the further investigation of the affecting mechanism, the thermal collective devise was used to get the cooling curve. The results were below:(1) As Ce, Y were added respectively into high purity Mg-3A1 alloy increasively, the grain size was developing bigger. When they were added respectively into the melt, the second phase particles of Al11Ce3 and Al2Y were formed. As the particles were distributed at dentrite gap, their restriction on grain size was very limited. The reaction of Ce, Y with Al-C-0 nucleate respectively caused to form Al-C-Ce and A1lC-O-Y particles, so the numble and potency of nucleant particles were reduced and then the grain was caused to develop bigger.(2) Mg-3Al-xCe alloys were carbon inoculated, and then grain sizes of the Mg-3Al-xCe were reduced to a similar size(nearly 240μm).The mechanism was that the addition of C2Cl6 form Al-C-0 particle in the melt which helped to refine the grain. Mg-Al-xY alloys were carbon inoculated too, but the grain sizes just kept the same. There were two reasons for this:one is no existence of Al-C-0 particle in the melt after carbon inoculation; another is that Y's Q (Grain restricting factor) value is very low comparing to Ce, so Y would be more helpful for grain coarsening than Ce.(3)The thermal parameters for the solidification of Mg-3A1 alloy were studied here. The results revealed that Ce,Y's addition to Mg-3Al alloys caused to the increase of wetting angle and the decrease of nucleating percentage,so the grain was coarsening. And then, such alloys were added with C2Cl6, their thermal parameters reflected that such treatment lead to the reduce of wetting angle,the increase of nucleating percentage and so caused the refinement of grains.