含镁高硅铝合金中析出相的结构演变过程研究

The precipitate dynamics and kinetics of Mg bearing Al-Si alloys was thought to be consistent with wrought Al-Mg-Si alloy. The applicant found that wrought Al-12.7Si-0.7Mg exist two different precipitates after aging which is inconsistent with Al-Mg-Si alloy in previous studies, thereby putting forward the issue of precipitate dynamics and kinetics of Al alloy which Si content is far more than Mg. This study the artificial aging behavior of high purity Al-Si-Mg alloy was investigated using high resolution electron microscopy, high-angle annular dark-field scanning transmission electron microscopy and three-dimensional atom probe. The research focus on the following aspects: the study of the structure, composition, morphology, volume fraction, size and distribution of the precipitates change with aging process. To explore the nucleation and growth kinetics mechanism of aging precipitation using in differential scanning calorimetry curves. The effect of alloy elements, the thermal deformation on aging precipitation behavior of Al-Si-Mg alloy were discussed to reveal precipitates evolution of Mg bearing Al-Si alloys and Al-Mg-Si alloy.

含镁铝硅合金的时效过程的热力学和动力学问题和一直被认为与变形6xxx系Al-Mg-Si合金一致。申请者在前期研究中发现，Al-12.7Si-0.7Mg变形铝合金时效过程中产生两种不同于Al-Mg-Si合金的析出相，从而提出了硅含量远超镁元素时铝合金的时效析出热力学与动力学问题。本研究以高纯Al-Si-Mg合金作为基础研究的出发点，利用高分辨电镜、高角度环形暗场技术和三维原子探针，测定合金时效强化过程中析出相的结构、与基体界面的原子排布以及成分。重点研究时效过程中各强化相形貌、体积分数、尺寸及分布的变化规律；分析时效强化相在沉淀析出各阶段形核、长大的动力学机制；考察微量合金元素、热变形对Al-Si-Mg合金时效析出行为的影响，揭示含镁高硅铝合金和变形Al-Mg-Si合金析出相演变过程本质。

Al-12.5Si-0.7Mg变形合金时效过程中，椭球状和针状析出物共同存在。椭球状析出物与Al-Mg-Si合金中观察到的亚稳相一致；变形合金在160℃时效主要的球状析出相为G.P.区。变形合金在180℃时效主要的椭球状析出相为β″，还存在少量的B′相，变形合金经180℃时效后晶界的主要析出相为Type-A和β′相。合金在180℃时效时，延长时效时间不改变合金析出相。变形合金在200℃时效合金的主要的椭球状析出相为β″相和少量的B′相，还存在Type-A相。在160℃、180℃和200℃时效时针状析出相特征相同，与基体保持共格关系。沿着[001]Al方向观察到的黑点状析出相不是沿着<001>Al方向分布的针状析出相的横断面。变形铝硅合金主要强韧化机制是颗粒复合强化、细晶强化、固溶强化和沉淀强化。合金的析出序列为：过饱和固溶体α→G.P.区→β″相→ β′ +B型析出物+A型析出物+C型析出物→β相+Si相。项目研究期间，发表学术论文5篇。