Effect of pre-aging on precipitation behavior of Al-1.29Mg-1.22Si-0.68Cu-0.69Mn-0.3Fe-0.2Zn-0.1Ti alloy
(1. School of Mechanical Engineering, Shandong Institute of Light Industry, Ji’nan 250100, China;
2. College of Material and Chemical Engineering, Liaoning Institute of Technology,
Jinzhou 121001, China;
3. School of Materials and Metallurgy, Northeastern University, Shenyang 110004, China)
2. College of Material and Chemical Engineering, Liaoning Institute of Technology,
Jinzhou 121001, China;
3. School of Materials and Metallurgy, Northeastern University, Shenyang 110004, China)
Abstract: By means of Vickers-hardness and electrical conductivity measurements, DSC tests and TEM analyses, the effect of different pre-aging treatments on precipitation characteristic of the Al-1.29Mg-1.22Si-0.68Cu-0.69Mn-0.3Fe-0.2Fe-0.1Ti (mass fraction, %) alloy during subsequent artificial aging was investigated. The results indicate that with increasing pre-aging time from 2.5 min to 10 min at 170 ℃, the number of formed b″ nuclei increases, resulting in promoting artificial aging kinetics and enhancing peak hardness. The hardness of pre-aged alloy reduces within lower temperature range of non-isothermal aging and increases in early stage of isothermal aging at 170 ℃. The size and density of clusters in pre-aged samples determine the hardenability in early stage of artificial aging. Pre-aging has dual mechanisms: namely, clusters (b″ nuclei) formed by pre-aging can inhibit the precipitation of GP zones during natural aging, and can quicken the precipitation of b″ phase in the early stage of subsequent artificial aging.
Key words: aluminum alloys; pre-aging; non-isothermal aging; isothermal aging; b″ nucleus