【摘要】 对单向凝固的 Al—4.5%Cu 合金层状晶的宏观形态、微观结构和溶质分布进行了分析观察,并测定了它的力学性能。研究结果表明,由孪生发展而成的层状晶,起源于柱状晶的生长界面上,在生长过程中伴随着层片的增殖。层状晶枝晶主轴的生长方向为<112>,二次分枝的生长方向为<100>和<110>。层状晶枝晶主轴中心的铜含量比柱状晶高,主轴内铜的分布比柱状晶均匀。层状晶的纵、横向抗拉强度与柱状晶相近,而伸长率则比后者高约40%。层状晶的力学性能与层片间距和层片交叉情况有关。更多还原

【Abstract】 Feathery structures often occurring in unidirectionally solidified alloyshave received only scant attention.It is not well understood even howfeathery grains are formed and in what kind of material they are liable tooccur.The purpose of this work is to investigate the morphology and me-chanical properties of feathery grains and to clarify the mechanism andconditions of their formation.In Part Ⅰ the morphology,solute distribution and mechanical propertiesof unidirectionally solidified ingots of Al-4.5% Cu alloy with featherystructure are discussed on the basis of experimental results.Structuralcharacteristics of feathery grains are studied by metallographic and scanning electron microscopic examination.The major findings are as follows:（1）Feathery grains develop from growth twins originating at the solid-liquid interface of columnar grain tips and the lamina multiplication occursin the course of growth.（2）The copper content in the primary arm center of feathery dendriteis higher than that of columnar dendrite and the copper distribution in theprimary arm of the former is more homogeneous than the latter.The resultsof electron-beam microanalysis indicate a distinct kinetics in feathery dendritegrowth.（3）Micro-structure analysis shows that the growth direction of theprimary arms of feathery dendrites is<112>and that of the secondary armsis<100>and/or<110>.（4）The primary arm spacing of a feathery grain depends on both thecooling rate and the distance from the place of origin of growth twin.Therelationship between secondary arm spacing and cooling rate for Al-4.5% Cualloy can be described by the empirical equation λ₂=243∈^-0.341.（5）Tensile tests reveal that both longitudinal and transverse tensilestrength of the ingots with feathery structure are respectively close to thecorresponding strength of the ingots with columnar structure but the percentof elongation of the former is～40% higher than that of the latter.Furthermore,the mechanical properties of feathery grains depend on both the lamina spacingand the degree of complexity of lamina intersections.Some data of tensileproperties of Al-4.5% Cu with feathery grains are presented.更多还原