China Foundry
Title: Microstructure evolution and precipitation behavior of Al-Mg-Si alloy during initial aging
Author: *Ya-ya Zheng1, 3, Bing-hui Luo2, Wei Xie3, and Wang Li1
Address: 1. Department of Materials Engineering, Hunan University of Humanities, Science and Technology, Loudi 417000, Hunan, China; 2. College of Materials Science and Engineering, Central South University, Changsha 410083, China; 3. Key Laboratory of Safety Design and Reliability Technology for Engineering Vehicle, Changsha University of Science & Technology, Changsha 410114, China
Key words: Al-Mg-Si alloy; precipitation behavior; strengthening mechanism; strain field; β″
CLC Nmuber: TG146.21
Document Code: A
Article ID: 1672-6421(2023)01-057-06
Abstract:
The microstructure evolution and precipitation behavior of Al-Mg-Si alloy during initial aging were studied using hardness testing, conductivity testing, differential scanning calorimetry (DSC), and high resolution transmission electron microscopy (HRTEM). The results show that the precipitation sequence of the Al-Mg-Si alloy during initial aging can be represented as: supersaturated solid solution → spherical Mg/Si clusters → needle-like Guinier Preston (GP) zone → β″. Clusters are completely coherent with the Al matrix. The GP zone with relatively complete independent lattice parameters that differ slightly from the Al matrix parameters, is oriented along the direction of <111>Al and lying on {111}Al plane. The strength of the Al-Mg-Si alloy is greatly enhanced by the threedimensional strain field that exists between the β″ phase and the two {200}Al planes. After aging at 170 °C for 6 h, the hardness reaches the peak of 127 HV and remains for a long time. At this stage, the electrical conductivity keeps relatively stable due to the formation of coherent precipitates (Mg/Si clusters/GP zones) and the reduction in solute atom concentration in the Al matrix. The severe coarsening and decreased number density of the β″ phase during the over-aging stage result in a significant decrease in the hardness.