The effect of Sn or In addition on natural ageing and subsequent artificial ageing of Al–Mg–Si alloys was investigated. In addition not only retarded the natural ageing but also improved the T6 hardness. Although Sn addition retarded the natural ageing as well, precipitation kinetics was delayed. In addition, slightly refined the β′′ phase distribution. But β′′ phase was coarse with addition of Sn. During artificial ageing, the vacancies released from binding complexes promote the formation of β′′. The detrimental effects of Sn on artificial ageing could be attributed to the reduction of the amount of Sn solutes and of available Mg solutes forming β′′.

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Al-Zn-Mg-Cu alloy have been widely used in aerospace industry. However, there is still a lack of research on thermal stability of Al-Zn-Mg-Cu alloy products. In the present work, an Al-Zn-Mg-Cu alloy with T79 and T74 states was placed in the corresponding environment for thermal exposure experiments. Performance was measured by tensile strength, hardness and electrical conductivity. In this paper, precipitation observation was analyzed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM). The precipitations of T79 state alloy were GPⅡ zone, η' phase and η phase while the ultimate tensile strength, hardness and electrical conductivity were 571MPa, 188.2HV and 22.2MS×m-1, respectively. The mechanical property of T79 state alloy decreased to 530MPa and 168.5HV after thermal exposure. The diameter of precipitate increased and the precipitations become η' and η phase at the same time. During the entire thermal exposure, T74 state alloy had the same mechanical property trend as T79 state alloy. The precipitate diameter also increased while the types of precipitate did not change under thermal exposure. The size of precipitates affected the choice of dislocation passing through the particles to affect the mechanical properties.

Abstract：In order to explore the resource of electric furnace slag, the mechanical properties and engineering application of electric furnace slag mixed soil are investigated in this paper. First, the mixed soil was prepared by mixing the steel slag and clay mixture in different proportions. Then optimal ratio method for mixed soil is explored with direct shear test. Second, the model parameters of the optimal ratio steel slag mixed soil are determined by the three axial compression tests. Finally, a practical engineering case is selected as numerical simulation object. The optimal ratio of slag mixed soil is used to replace the original subgrade, the deformation of the replaced embankment calculated and compared with that of the original one. The comparison results show that the method proposed in this paper is simple and effective, and can realize the resource utilization of electric furnace slag. Keywords: Electric furnace steel slag mixed soil; Direct shear test; Optimum moisture content; Numerical simulation IntroductionWith the rapid growth of steel production, steel slag keeps in the continuous accumulation as a by-product of steel production. The domestic production of steel slag is about 100 million tons in 2014. And it has been accumulated over 1 billion tons. But the comprehensive ratio of utilization of domestic steel slag is only about 10% [1] . The accumulation of steel slag leads to a lot of environmental pollution, and take up a lot of land. Some researchers [2][3][4][5][6][7] have researched steel slag utilization, exploring the steel slag application in road engineering, building materials, etc. Since the steel slag's high hardness, high strength, low amount of compression, and the water activity features [8,9] , it is widely used in foundation, roadbed treatment in recent years. With crude steel production growth slowing and steel storage increasing in China, the quantity of electric furnace steel will increase a lot ［10］ . So, in a lot of small and medium-sized city industrial waste pollution, electric furnace steel slag is more representative. At present, the recycling of the advanced electric furnace slag oxidation technology is rarely reported. Therefore, electric furnace oxidizing slag utilization research is of great significance and essential. In this work, furnace steel slag of the area of Huangshi is selected as the research object, explores a way of fast shear to obtain the optimal ratio of steel slag mixed soil, then through conventional tri-axial compression trail determining the optimal proportion of mixed soil mechanics parameters. And carrying the 752 numerical simulation for the embankment of the test section, settlements in soft soil roadbed are compared with the slag mixture soil roadbed, so as to obtain the electric furnace steel slag application system engineering method and the laws. Direct shear test and the optimal matching Materials for experimentThe main raw materials are steel slag and soil engineering, among them, the electric furnace steel slag from a steel mill tai...