冷却速率对Mg68Zn28Y4自生复合材料I相形成的影响

采用两种不同冷却方式的普通铸造技术在Mg68Zn28Y4合金中制备了镁合金稳定态二十面体准晶相,分析了冷却速率对准晶相形成、分布、数量和晶粒尺寸的影响.通过扫描电镜、能谱分析仪和透射电子显微分析技术,确定了合金的组织、相成分及准晶相结构.结果表明:Mg68Zn28Y4三元合金在室温冷却过程中,准晶相直接从液相形核、长大;在铸铁模型腔内冷却时,铸件断面的温度梯度小,温度场较为平坦,沿铸型纵横截面准晶相分布均匀、晶粒尺寸约为10～15μm;在铸铁板表面冷却时,铸件断面的温度梯度较大,导致冷却速率显著影响准晶相的分布、数量及形貌.准晶相的晶粒尺寸为10～60μm不等,分布由均匀弥散到不均匀散布再到均匀.

Effect of cooling rate on I-phase formation in as-cast Mg68Zn28Y4 in-situ composites

In Mg68 Zn28 Y4alloys,stable icosahedral quasi crystals(Zn60 Mg30 Y10) were prepared by as-cast method with two different cooling ways.Different cooling rates were analyzed to study the effects on I-phase formation,amounts,distribution and grain size.The microstructure,composition and phases were analyzed by SEM and EDS.The structure of quasi crystal phase was identified by TEM.Results show that the I-phases directly nucleate and grow from the melt of cooling Mg68Zn28Y4 ternary alloys at room temperture.The circular degree and the granularity of the quasi crystalline demonstrate no difference between vertical section and horizontal section in the castiron mould,and I-phases evenly distribute with 10-15 μm grain size.It can be seen that the effect of cooling rates on formation and distribution of quasicrystals in as-cast Mg68Zn28Y4 alloy is not remarkable in the conditions of low cooling rate and small casting.However,cooling on the castiron surface causes the change of circular-degree and grain size of I-phases from the castiron cooling surface to the room cooling surface,and the distribution is affected remarkably by cooling rates.Five-fold icosahedral quasicrytal Zn60Mg30Y10,which appears in five petal shapes or in small pentagonal grains,is dispersed on the matrix with 10-60 μm grain size.