Composition optimization of high-strength Mg-Gd-Y-Zr alloys based on the structural unit of Mg-Gd solid solution

Mg-Gd-Y-Zr alloys with high strength fall within narrow composition range.The present paper explains their composition rule by establishing the cluster-plus-glue-atom unit of Gd-containing Mg solid solution with the aid of Mg matrix and Mg_(5) Gd precipitate phase.First,based on the structural homologue between Gd-containing Mg solid solution and Mg_(5) Gd precipitate phase and in combination with our previously established method for calculating the glue atoms,[Gd-Mg_(12)]Mg_(5) is obtained as the chemical unit of Gd-containing Mg solid solution.Then,seven compositions are designed using different combinations of this unit and that of pure Mg[Mg-Mg_(12)Mg3.After a systematic experimental investigation on the microstructure and mechanical property evolutions as a function of the unit proportions,it is revealed that the Mg-10.1 Gd-3.3 Y-0.9 Zr alloy,being issued from equi-proportion mixing of the two units,shows the strongest tendency of precipitation and reaches the highest strength of 374 MPa after aging.The composition and strength of this alloy are quite close to GW103 K which is well recognized for its general mechanical performance in Mg-Gd-Y-Zr system.

金属合金中的类分子化学结构单元

本文引入Friedel振荡理论,揭示固溶体合金中存在类似分子式的结构单元,指出在特定的成分下,合金中的原子在近程序上倾向于聚集为理想的有序结构,这个结构包括最近邻壳层原子(记作团簇)和次近邻壳层原子(记作连接原子),用团簇式:[团簇](连接原子)来表示.这种近程序结构被称为化学结构单元,类似于固溶体中的"分子".本文给出了FCC结构固溶体合金中化学结构单元的计算公式,通过计算得到Cu基二元体系的理想化学结构单元,包括CuZn、Cu-Al、Cu-Ni、Cu-Be和Cu-Sn,均为工业中最常用的合金成分.此外,工业上常用的多元合金,如Al合金5083和7075、高温合金TMS-196和TMS-82、马氏体时效不锈钢Cutom-465和奥氏体不锈钢310s,其成分均满足模型的预测,表明本模型可以为FCC结构复杂固溶体合金的成分设计提供理论指导.