The Theories And Experiments Of Al-Si-Mg Alloy Ageing

In this paper, the ageing precipitation and age-hardening of Al-Si-Mg alloy series were researched by thermal analyzer (TA), optical microscope (OM), scanning electronic microscope (SEM) and energy disperse spectroscopy (EDS) and some other testing methods. The EET theory was used to calculate the electron structures of the cells appeared during ageing of Al-Si-Mg alloy, and the results were used to explaned precipitation process. The models of rod shaped precipitate were used to predicte the density and size of precipitates and the age hardening effect of Al-7Si-0.55Mg alloy varying with aging time.(1) Eight cells appeared during ageing of Al-Si-Mg alloy, which includedα-Al,α-Mg,α-Si,α-AlMg,α-AlSi,α-AlSiMg, Mg₂Si, G.P. zone. Their electron structures were calculated by the BLD method in EET theory. The driving mechanism and precipitation process of the Al-Si-Mg alloy ageing were concluded by analysing the electron structures. The conclusions of theory analyce agreed with the results of experiments.(2) The nucleation and growth processes of rod shaped precipitates and the age hardening process were modeled by some assumptions based on the precipitation thermodynamics, the traditional nucleation dynamics and the dislocation strengthening theories. The density and size of precipitates and the age hardening effect of Al-7Si-0.55Mg alloy varying with aging time were predicted. The largest hardness given by experiment appeared earlier than the one given by the theory, because the thickeness of the sample was neglected.(3) The ageing precipitation behavior was characterized by electrochemical corrosion parameters included corrosion potential and corrosion current density in this paper.