单辊快速凝固Mg-4.8Zn-0.6Y合金的组织

Microstructures Characterization of Melt-spun Rapidly Solidified Mg-4.8Zn-0.6 YAlloy

采用单辊快速凝固方法制备了Mg-4.8Zn-0.6Y合金薄带,利用SEM、TEM、XRD、EDX及DTA,研究了合金的显微组织、相组成、偏析及凝固特征。结果表明,快速凝固制备的Mg-4.8Zn-0.6Y合金由过饱和的α-Mg固溶体、准晶I（Mg3YZn6）和X（Mg12YZn）相组成,自由表面晶粒为1～3μm的细小等轴晶。凝固过程的冷却速度为4.60×106～1.04×107 K·s-1,满足准晶相析出所需的冷却条件。沿薄带厚度截面Mg、Zn和Y的分布比较均匀,仅存在少量偏析,晶内也存在微观偏析。偏析是由于从辊面到自由面凝固速度的差异及溶质传输和晶格结构造成的,其中Zn元素偏析最大,Y次之,Mg最小。

The rapidly solidified Mg-4.8Zn-0.6Y ribbons were prepared by melt-spun rapidly solidification with a single roller. The microstructures, phase constituent, micro-segregation and solidification characteristics of the alloy were investigated by SEM, TEM, XRD, EDX and DTA. The results show that the microstructure of rapidly solidified Mg-4.8Zn-0.6Y ribbons consists of a-Mg supersaturation solid solution, quasicrystals I（Mg3YZn6） and X（Mg12YZn）, and the fine equiaxed grain size in free surface rea- ches 1～3μm. It indicates that the cooling rate of rapid solidification about 4.60×10^6～1.04 ×107 K·s-1 meets the cooling conditions of quasicrystalline phase precipitation. Magnesium, zinc and yttrium are distributed uniformly along thickness cross section of the rapidly solidified ribbon, however, there exists a small amount of microsegregation in the thickness of ribbons and within the grains as well. Microsegregation is attributed to the difference from the copper substrate to the free surface of ribbons and the solidification velocity rate of solute transport and lattice structure, and for the segregation trend of three elements, Zn is the largest, and then Y,Mg.