Precipitation of metastable phases and its effect on electrical resistivity of Al-0.96Mg2Si alloy during aging
(1. Shandong Innovation Alloy Institute, Zouping 256200, China;
2. School of Materials and Engineering, Central South University, Changsha 410083, China)
2. School of Materials and Engineering, Central South University, Changsha 410083, China)
Abstract: The precipitation behavior and its influence on the electrical resistivity of the Al-0.96Mg2Si alloy during aging were investigated with in-situ resistivity measurement and transmission electron microscopy (TEM). The precipitates of the peak aged alloy include both β″ and β′, but the amount ratio of β″ to β′ varies with the aging temperature and time increasing. The precipitates during aging at 175 °C are dominated by needle-like β″ phases (including pre-β″ phase), the size of which increases with the time prolonging, but does not increase substantially after further aging. The evolution of electrical conductivity is directly related to such microstructural evolution. However, the hardness of the alloy stays at the peak value for a long term. When the alloy is aged at 195 °C, the ratio of β″ to β′ becomes the main factor to influence relative resistivity (？ρ) value. The higher the temperature is, the smaller the ratio is, and the faster the ？ρ value decreases. Moreover, the hardness peak drops with the decrease of the ratio. With the size and distribution parameters measured from TEM images, a semi-quantitative relationship between precipitates and the electrical resistivity was established.
Key words: Al-Mg-Si alloy; metastable phases; electrical resistivity; aging; precipitate