The Study on Precipitation Kinetics for β″ Phase of Al-Mg-Si-Zr-XEr Alloy

Abstract:

By means of performance testing, microstructure and differential thermal analysis, the hardness-time curves, TEM microstructures, TTT curves and precipitate activation energy of β″ phase for Al-Mg-Si-Zr-XEr alloy were investigated, and kinetics expressions and TTT expressions of β″ phase were acquired. The results show that the addition of Er element accelerates the dispersively precipitation of the β″ phase, and the fine and uniform β″ phase of Al-Mg-Si-Zr-0.3Er alloy precipitate dispersively after the solution treatment at 540 ℃ for 1 h and aging at 180 ℃ for 5 h. As the element Er content increases, hardening rate of alloy is significantly accelerated, softening rate of alloy is decreased, precipitate activation energy of β″ phase for alloy is decreased, and the values are 96.3, 93.6 and 84.9 kJ/mol. The kinetics expressions are obtained as follows, YEr0.1=1-exp[-1.534×1013t1.5exp(-17382.7/T)], YEr0.2=1-exp[-5.865×1012t1.5exp(-16895.3/T)], YEr0.3=1-exp[-2.965×1011t1.5exp(-15324.9/ T)]. The TTT expressions are obtained as follows, TEr0.1=17382.7/[30.4 1.5lnt-lnln(1-Y)-1], TEr0.2=16895.3/[29.4 1.5lnt-lnln(1-Y)-1], TEr0.3=15324.9/[26.4 1.5lnt-lnln(1-Y)-1].

Key words:Al-Mg-Si alloy; β″ phase; precipitation kinetics; TTT curves