The Effect Of Si Content On The Microstructure And Properties Of AM60/AlSi Liquid-Solid Interfacial Bonding

Magnesium alloy and aluminum alloy both are the important metal materials in modern automobile industry.Due to the advantages of light weight and high specific strength,magnesium alloy has been widely applied to the automobile manufacture,resulting in automobile lightweight and pollution reduction.Aluminum alloy has been widely used in the automotive industry and other fields,because of its superior mechanical properties and corrosion resistance.Ideally,combining the best aspects of both alloys would be most convenient for application in these areas.Therefore,the study on the Mg/Al dissimilar metal based composite structure has become a hot research topic.However,it is necessary to overcome two difficulties in its application in order to obtain good bonding properties of Mg/Al dissimilar metal.On one hand,the compact oxidation film forming on the surface of Al substrates prevents the metallurgical combination between the aluminum and magnesium.On the other hand,the mutual solubility between the two materials is very small,leading to the formation of many intermediate compound in the interface which can play negative effect on the mechanical properties.Taking the difficulties into account,firstly,in this paper,two methods were adopted to remove the oxide film on the surface of aluminum substrate,which were high temperature surface treatment via aluminum brazing solvent QJ207 and Zincate surface treatment.Then the influence of the varied Si content on the intermetallic compounds as well as the effect of cooling rate on the thickness of the transition layer were explored.The details can show as follows:1.Two methods of the removal of the oxide film on the aluminum substrate surface: 1)the application of QJ207 in a vacuum environment can prevent the regeneration of the oxide film;2)Zincate surface treatment can remove the oxide film and replace it with a metallic zinc film via two parallel chemical reactions.Compared to the latter approach,the former one shows easier removal of the oxide film in the paper,due to the improvement of surface wettability on account of the surface-active agent in QJ207.However,zincate surface treatment is better suited in practice,attributed to being simple to operate as well as applicable to the fabrication of the components with complex shapes.2.The influence of the varied silicon content in the aluminum substrate on the liquid-solid interface: When the mass fraction of silicon reached 1.7%,Mg₂Si formed in the interfacial microstructure.When the content of Si reached 5.5%,Mg₂Si particles canconnect with each other,resulting in the formation of the Mg₂Si layer.When the content of Si added up to 12.5%,the Mg₂Si layer would go down to the interfacial surface completely.Because of the blocking effect of Mg₂Si layer,brittle phase and the thickness of the transition layer can be reduced effectively.3.The influence of cooling rate on the thickness of the transition layer of AM60/Al-5.5Si: It is found that the faster the cooling rate of the sample is,the closer is the formation of the Mg₂Si layer onto the aluminum substrate,which can remarkably reduce the thickness of the transition layer.