不同凝固条件下Mg_(95.81)Zn_(3.60)Y_(0.59)合金凝固过程及凝固组织

Solidification process and solidified microstructure of Mg_(95.81)Zn_(3.60)Y_(0.59) alloy under different solidification conditions

采用Factsage热化学软件计算了平衡条件和Scheil条件下实验合金的凝固路径及相组成。在与之对比基础上研究了常规铸造(金属型)和4 GPa高压下凝固的实验合金凝固过程和相组成。结果表明:金属型铸造下,四相包共晶转变和随后的WMg_3Y_2Zn_3相分解不充分,室温下凝固组织由α-Mg基体,W-Mg_3Y_2Zn_3和I-Mg_3YZn_6相组成。4 GPa高压下凝固时,因液相线温度升高及单位面积α-Mg晶体形核率大幅增多,使α-Mg相所占体积分数增多,分布在枝晶间最后凝固的共晶液相发生偏析型离异共晶转变,生成面积尺寸很小的骨骼状共晶相半连续分布在枝晶间。4 GPa高压下凝固时,当熔体过热度很小时,初生晶α-Mg为规则的、分枝不发达的等轴晶(晶粒尺寸为20μm);随熔体过热度升高,不但晶粒尺寸增大,枝晶分叉、二次枝晶重熔、破碎等现象也逐渐显现;4 GPa高压下凝固组织由α-Mg+I-Mg_3YZn_6相组成。

Solidification paths and phase constituents of Mg_（95.81）Zn_（3.60）Y_（0.59） alloy under equilibrium solidification and Scheil solidification conditions had been calculated by Factsage.The solidification process and phase constituents of the alloy solidified under atmospheric pressure（ metal mold） and 4 GPa high pressure were also investaged for comparison.It is shown that under the metal mold condition,four phase peritectic transformation and W-Mg_3Zn_3Y_2 separation are insufficient,and the solidified microstructure consists of α-Mg,W-Mg_3Zn_3Y_2 and I-Mg_3Zn_6Y.Solidified under 4 GPa high pressure,the liquidus temperature is increased and the α-Mg nucleation rate in unit area sharply increases,which can be contributed to the increase of the volume fraction of α-Mg,the last solidified eutectic liquidphase distributed in the interdendritic region carry on segregation type divorced eutectic transformation,and then there are bone eutectic phase semi-continuously distributed in interdendritic region.Solidified under 4 GPa high pressure,when in low melt superheat,primaryα-Mg grains are regular with the grain size of 20 μm; with increasing of the melt superheat,not only grain size increases but the phenomenon of dendrite branching,secondary dendrite remelting and crushing also gradually appears.The solidified microstructure consists of α-Mg and I-Mg_3YZn_6 under 4 GPa high pressure.