时效早期Al-Mg-Si合金的组织和析出相的演变

用显微硬度测试、差示扫描量热法(DSC)和高分辨透射电镜(HRTEM)观察等手段研究了Al-Mg-Si合金人工时效过程中的硬化、组织变化以及早期析出相的演变。结果表明：在170℃时效的合金具有更高的峰值硬度。在时效初期晶内析出高数量密度的溶质原子团簇和GP区，合金的硬度显著提高。在170℃处理4 h后合金的硬度达到峰值，此时晶内析出相以针状β″相为主，β″相与Al基体界面三维共格应变是合金强化的主要原因。同时，晶界析出相呈断续分布状态。随着时效时间的增加β″相开始粗化，晶界析出相的连续程度降低。在过时效阶段晶内析出相的严重粗化和数量密度的降低，使合金的硬度剧烈降低。在时效的初始阶段，合金的析出序列为过饱和固溶体→球形原子团簇→针状GP区→针状β″相。

Evolution of Microstructure and Precipitates of Al-Mg-Si Alloy during Early Aging Process

The evolution of hardening, microstructure and precipitate of Al-Mg-Si alloy during early artificial aging process were investigated by means of microhardness tester, differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM). The results show that the alloy aged at 170℃ has higher peak hardness. At the early aging stage, the high number of solute clusters and GP regions precipitated within grains, and the hardness of the alloy significantly increased. The hardness of the alloy reaches the peak value after being treated at 170℃ for 4 h, and the acicular β"-phase is the main precipitated phase within grains. The three-dimensional coherent strain at the interface between β"-phase and Al matrix is the main reason for the strengthening of the alloy. At the same time, the precipitated particulates distributed discontinuously along grain boundary. With the increase of aging time, the β"-phase coarsened and the continuity of the precipitated particulates decreased. During the over-aging stage, the hardness of the alloy is greatly reduced due to the severe coarsening and the decrease of number of the precipitates. At the initial stage of aging, the precipitation sequence of the alloy is as follows: supersaturated solid solution → spherical atomic clusters → needle-like GP region → needle-like β"-phase.