Mg-14.61Gd合金的定向凝固组织及生长取向

As one of the most promising heat-resistant magnesium alloys, Mg-Gd series alloy has a wide application prospect in the industrial fields of aerospace, cars, and rail transit. There have been extensive researches on the performance improvement of Mg-Gd series alloys. As known, dendrites are the common solidification microstructures of castings of magnesium alloys, and solidification conditions have a significant effect on dendrite morphologies and growth orientation, which could strongly affect the mechanical properties of castings, thus it is critical to study the grain growth regularity for predicting the performance of magnesium castings. However, there are few studies on numerical simulation of dendrite growth process and growth orientation of magnesium alloys. Solidification behavior of magnesium alloys can be scientifically studied via directional solidification technology, and cellular automaton finite element (CAFE) method should be effective to simulate the dendrite growth process of magnesium alloys. In present work, microstructures and growth orientation of directionally solidified Mg-14.61Gd alloy under the temperature gradient G=30 K/mm and the withdrawal rate v=10~200 mm/s were investigated by EBSD measurement method and CAFE numerical simulation method. It was found that a-Mg primary phase presented unidirectional dendritic morphologies on longitudinal cross-section. The growth interface appearance of α-Mg changed from the protruding forward growth to the flat growth gradually and the dendritic arm spacing decreased gradually with the increasing v. when v increased from 10 mm/s to 100 μm/s, the main growth orientation of α-Mg changed from <1120> and <1010> to <1120>, and the deviation angle (θ) from solidification heat flow direction reduced from 11.0° to 5.7°, the reason for this lied mainly in the change of the heat flux. Further increasing v up to 200 mm/s, the main growth direction of α-Mg was still in <1120>, but the value of q increased to 10.6°, and the anisotropy of the crystal was the dominant factor then. It was proved that the CAFE numerical simulation model could predict the grain structure and growth orientation reasonably for Mg alloy.