Mg-Gd-Y-Zr合金可控冷却速率实验方法及凝固组织的X射线断层扫描表征

Preparation of Mg-Gd-Y-Zr alloy solidified at controlled cooling rate and microstructure characterization by X-ray tomography

建立了可控冷却速率的实验方法、凝固过程测温方案和合金内部温度推算方法,对Mg-6Gd-3Y-0.5Zr(质量分数,%)(GW63K)合金开展可控冷却速率实验,结合X射线断层扫描技术、扫描电子显微镜和X射线能谱分析等实验表征手段,表征可控冷速镁合金的凝固组织形貌并获取定量信息,研究了冷却速率对GW63K合金凝固组织微观形貌、定量信息的影响和变化规律。结果表明:在GW63K合金凝固组织中,共晶呈网络状分布在晶界处,形状不规则的第二相呈岛状分布在共晶组织中;平均冷却速率R_(c)在0.13~0.33℃/s范围内,随着冷却速率的增加,网状共晶组织更密集、均匀和连续,第二相分布更均匀、尺寸更小,微观溶质偏析减小,第二相和共晶体积分数均呈下降趋势。

An experimental method of preparing Mg-Gd-Y-Zr alloy solidified at controlled cooling rate,acquiring temperature-time data during the solidification process,and calculating the temperature inside the alloy was established.The experiments were carried out on Mg-6Gd-3Y-0.5Zr(mass fraction,%)(GW63K)alloys,and several GW63K alloy specimens cooled at different rates in the range of 0.13-0.33℃/s were prepared.The solidification microstructure and quantitative information of the GW63K alloys were characterized by using X-ray tomography technique and SEM.The effects of cooling rate on the microstructure and quantitative information were discussed.Besides,the quantitative relationships between cooling rate and volume fractions of the eutectics and secondary phase were proposed,respectively.The results show that the eutectics of GW63K alloy which distribute at the grain boundaries present network-like morphology,and the secondary phase with irregular morphology distributes in the eutectics.With the increase of cooling rate in the range of 0.13-0.33℃/s,the primary phase with six-fold symmetry is refined.The eutectic networks become denser,more homogeneous and continuous.The secondary phase distributed more dispersively,and the average size of secondary phase become lower.In addition,the volume fractions of eutectics and secondary phase reduce with increasing the cooling rate.