Precipitation behavior and hardening effects of Si-containing dispersoids in Al-7Si-Mg alloy during solution treatment

The precipitation behavior and hardening effects of Si-containing dispersoids in Al-7Si-Mgalloy solution-treated at 505 degrees C, 535 degrees C, and 550 degrees C for various times are studied mainly through metallographic observation, scanning electron microscope characterization, electron probe microanalysis measurement, and micro-hardness test. The solute concentrations in the matrix, and the area fraction and equivalent diameter of the Si-containing dispersoids are quantitatively measured. The composition of the dispersoids mainly consists of Al with a small amount of Si and Ti. The results reveal that the distribution of Ti controls the nucleation of the dispersoids and is the dominant mechanism for the formation of the dispersoid-free zone. The precipitation kinetics of the dispersoids is enhanced with an increase in the solution temperature. The Si-rich particles existing in the matrix can promote the growth of Si-containing dispersoids because the diffusion distance of silicon atoms towards the dispersoids is much smaller. Further, it shows that the hardening effect of Si-containing dispersoids is weak compared with the contribution of solid solution strengthening. Long solution treatment times will enhance the depletion of Mg in the matrix and reduce the subsequent aging hardening. (c) 2015 Elsevier Ltd. All rights reserved.