The Effect Of Sn On The Microstructure And Mechanical Property Of Liquid-solid Bonding Interfaces Of AM60/6061 Alloys

In recent years aluminum and magnesium and their alloys have been widely used in aerospace and automobile manufacturing as the main non-ferrous metal materials. In the study of the weight reducing of cars which lays emphasis on energy-saving and environment protection, the engine made of aluminum/magnesium liquid-solid composite materials possesses some positive qualities such as magnesium alloy with lower density, good ductility, strong resistant impulses and aluminum alloys with high-strength, better plasticity as well as good corrosion resistance, which has a remarkable economic returns and great market prospect.Liquid-solid diffusion bonding process was used for production of Mg/Al couples, which is a new technology connecting dissimilar materials. In this paper, the effects of the surface treatment of 6061 aluminum on the interface of liquid-solid composite casting were studied as well as the tin addition modification treatment. The main contents are as following:1. Pre-treatment of the 6061 aluminum alloy substrate. It is the natural oxide layer on the 6061 aluminum substrate that deeply prevents the formation of a continuous metallurgic joint with magnesium alloy, which can form again soon after mechanical polishing. The results show that such coating can effectively improve AM60/6061 liquid-solid composite wettability via the visual observation and simply tests.2. Modification treatment of magnesium alloy. The amount of tin addition can refine magnesium grains and improve the properties of magnesium alloys. In this thesis, two ways adopt to adding tin, tin dipping and tin adding directly. The experimental results suggest that, the microscopic structure can improve effectively with magnesium alloy modification by proper tin addition, appearing the distribution of diffuse Mg2Sn granules.3. Microstructure and properties of the transition layer. The bimetallic samples were examined with optical microscope, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) system coupled with electron probe microanalysis (EPMA). The results show that the tin impeded the diffusion of magnesium, as a result preventing nucleation successfully and inhibiting the grain growth. Mg2Sn blocks dispersing in the dendritic crystals and eutectic grain boundaries improved the microstructures and properties of transition layers. With the tin content increasing, the shear strengths of the bimetallic samples would be improved, which increased first, and then decreased. The shear strength reached a peak value with 1% tin addition.