Improvement of Mechanical Properties of an Al-Li Alloy by means of Additional Elements

题为“通过添加元素改善铝锂合金的机械性能”的项目已在教育、科学和文化部的科学研究补助金下完成。结果表明：（1）含Zr、Ti、Hf的Al-Li合金在双时效过程中发生了复杂的沉淀。复合析出相由Al_3Li包围的Al_3M（M：Zr，Ti或Hf）组成，在第二次时效过程中Al_3Li长大。(2)所有析出相均为有序L1_2结构的亚稳相。(3)用透射电镜观察了各元素在时效过程中的作用。结果总结如下：Zr、Ti或Hf：这些元素中的每一种在高温下第一次时效期间以Al<@23<@D2M的形式析出。Cr：在第一次时效的早期，在晶界上以Al_7Cr的形式非均匀析出。析出物钉扎晶界，从而完全抑制晶界反应型析出（不连续析出）。结果表明，细小球形颗粒连续析出的面积增大，最大硬度显著提高。司：这加速了晶粒中的连续析出，因此也有助于这些时效合金的机械性能的改善。

The project entitled "Improvement of Mechanical Properties of an Al-Li Alloy by Means of Additional Elements" has been completed under the Grant-in-Aid for Scientific Research by The Ministry of Education, Science and Culture. Abstract of results obtained is as follows:(1) It has been found that a complex precipitation takes place during duble aging in Al-Li alloys containing Zr, Ti or Hf. The complex precipitates consist of Al_3M (M:Zr, Ti or Hf) surrounded by the Al_3Li, which grows during the second aging.(2) All precipitates are found to be metastable phase of ordered L1_2 structure.(3) Role of each element in the aging procedure has been investigated by microstructural observation by an transmission electron microscope. Results are summarized as follows:Zr, Ti or Hf : Each of these elements precipitates as Al<@23<@D2M during g the first aging at high temperature. This precipitates acts as the nuclei of the Al-<@D23@>D2Li formed during the second step of aging.Cr : This precipitates heterogeneous at grain boundaries as Al_7Cr at very early stage of the first aging. The precipitate pinned down the grain boundary, so that the precipitation of the grain boundary reaction type (discontinuous precipitation) was completely suppressed. As a result, area covered by the continuous precipitation of fine spherical particles increased, then the maximum hardness is improved remarkably. Si : This accelerates the continuous precipitation in grains, so that it also contributes the improvement of mechanical properties of these aged alloys.