Artificial aging precipitation behavior of 6000 series alloys naturally aged and pre-aged

By means of Vickers-hardness measurements,DSC tests and TEM analyses,the artificial aging precipitation behaviors of several 6000 alloys in natural aging and pre-aging tempers were investigated.It is indicated that GP zones' dissolution process of the T4(stored for two weeks at room temperature after solution treatment) alloys in the early stages of artificial aging at 170℃ delays the precipitation of β″ phase,and the precipitates formed are mainly β″ nuclei,decreasing aging hardenability.The β″ nuclei in the T4P(immediately aged at 170℃ for different time after solution treatment and then stored for two weeks at room temperature) alloys develop into β″ phase in the same stages and the microstructure is mainly composed of β″ phase,leading to enhancement of aging hardenability.The increase of pre-aging time can obtain better hardening effect of artificial aging.For the alloy with excess Si,the increment of Mg/Si mass ratio makes for the precipitation of β″ nuclei and improves artificial aging hardenability.