不同速率定向凝固条件Mg-1.5Gd镁合金的微观结构及微观偏析

Microstructures and Microsegregation of Directionally Solidified Mg-1.5Gd Magnesium Alloy with Different Growth Rate

摘要:

本文研究了在定向凝固条件下凝固速率对Mg-1.5Gd镁合金微观结构的影响。试样通过Bridgman定向凝固炉来制备，温度梯度恒定为40K/mm，凝固速率为10-200μm/s。研究发现，Mg-1.5Gd镁合金凝固组织为典型胞晶结构，通过线性拟合得到胞晶间距与凝固速率关系为：λ= 130.2827V-0.222，此结论与Trivedi模型拟合较好。通过Scheil模型进行热力学凝固路径计算，结合试验观察可以确定凝固组织为α(Mg)相和α(Mg) Mg5Gd二元共晶相。同时，通过Scheil模型计算所得的Gd元素的微观偏析与EPMA测量结果基本一致。

Abstract:

Directional solidified Mg-1.5Gd (wt.%) magnesium alloy was carried out to investigate the effects of the growth rate on the microstructures under controlled solidification conditions. A Bridgman-type directional solidification furnace with liquid metal cooling (LMC) technology was used to solidify the specimens, which could provide steady state conditions with a constant temperature gradient (40K/mm) at a wide range of growth rate (10-200μm/s). The microstructures were observed to be cellular structures, and the relationship between cellular spacing (λ) and growth rate (V) was established in the form: λ= 130.2827V-0.2228 by using a linear regression analysis, which was in good agreement with the calculated values by Trivedi model. The thermodynamics solidification path calculations by Scheil model and experimental observations confirm that the solidification microstructure in the alloy consists of primary α(Mg) phase and binary eutectic α(Mg) Mg5Gd phase. Meanwhile, the microsegregation of the alloying element predicted by the Scheil model agrees reasonably with the electron probe microanalysis (EPMA) measurements.