differential scanning calorimetry are used. To describe the evolution of the structure in ageing, the Avrami equation and the ageing time dependence of the ...
ISSN 10678212, Russian Journal of NonFerrous Metals, 2010, Vol. 51, No. 6, pp. 471–475. © Allerton Press, Inc., 2010. Original Russian Text © A.N. Solonin, A.Yu. Churyumov, A.V. Mikhailovskaya, M.A. Ryazantseva, M.G. Khomutov, 2010, published in Izvestiya VUZ. Tsvetnaya Metallurgiya, 2010, No. 6, pp. 34–38.
PHYSICAL METALLURGY AND HEAT TREATMENT
Modeling the Evolution of the Structure and Properties of Alloys for an Al–Zn–Mg System in Ageing A. N. Solonina, A. Yu. Churyumovb, A. V. Mikhailovskayac, M. A. Ryazantsevad, and M. G. Khomutove Moscow Institute of Steel and Alloys, National Research Technology University, Leninskii pr. 4, Moscow, 119049 Russia a email: solonin@misis.ru bemail: churyumov@misis.ru c email: mihaylovskaya@bk.ru demail: mariyaryaz@yandex.ru e email: makc@chelny.com Abstract—An investigation into and modeling of artificial ageing in alloys of an Al–Zn–Mg system are car ried out. To determine the kinetic parameters of the dissociation of a supersaturated solid solution, methods of transmission electron microscopy, a measurement of electric resistance at heightened temperature, and differential scanning calorimetry are used. To describe the evolution of the structure in ageing, the Avrami equation and the ageing time dependence of the particle size are applied. A comparison between the compu tational and experimental values of particle sizes showed the sufficiently high accuracy of the model. Based on this, the yield strength for alloys of the system under consideration in the aged state was computed. The computational error was 11%, which is comparable with the error of the experimental determination of the yield strength. Keywords: Aluminum alloys, artificial ageing, Al–Zn–Mg system, modeling, yield strength, evolution of structure. DOI: 10.3103/S1067821210060076
INTRODUCTION Right now, mathematical modeling is used to solve many problems of physical metallurgy, such as fore casting the structure and properties of materials and optimization of alloy production techniques. Consid erable attention is given to processes of ageing alumi num alloys. This problem is considered in a significant number of publications, both in the domestic and for eign literature [1–8]. However, most models are not accurate enough for a complete quantitative descrip tion of the processes occurring during the dissociation of supersaturated solid solutions in aluminum alloys. This work gives a methodology that we developed to construct the models for the evolution of the struc ture of aluminum alloys during thermodiffusion treat ment. Using it, a model for the evolution of the struc ture of alloys of an Al–Zn–Mg system was obtained.
To apply them as charge materials, we use A99 alu minum, Ts0 zink, and Mg90 magnesium. Melting was carried out in an electric resistance furnace in a graph itefireclay crucible; the melt was poured into a graph ite mould. The sizes of ingots were 150 × 50 × 15 mm. The castings were homogenized in an electric muf fle furnace according to the mode; namely, 420°C for 3 h and 450°C for 10 h. Ageing for samples was carried out with various holding times at Tag = 110–200°C in a SNOL 58/350 drying cabinet. The standard samples were tension tested at room temperature by a Zwick Z250 universal test machine. The change in electrical resistance during ageing at 140, 170, and 200°C was recorded by a GW INSTEK Table 1. Composition of the alloys under investigation according to the data of spectral analysis Content, wt % Alloy
OBJECT AND TECHNIQUE OF INVESTIGATIONS Model alloys of the Al–Zn–Mg system were selected as objects for investigation. Their composi tion is listed in Table 1. 471
1 2 3
Al
Zn
Mg
Si
Fe
84.9 96.8 91.5
12.7 2.7 6.0
2.4 0.5 2.5
