Investigation Of Interfacial Structure And Performance Of Liquid-solid Diffusion-bonded Mg/Al Bimetallic Casting

In recent years, with the development of industry, energy crisis and environment problem increasingly serious, the demand for materials of people is increasingly high, lightweight and high performance have become a trend in the development of new materials. A single material has been difficult to meet modern industrial production process of various requirements for the material. The bimetal composite material due to combine the advantages of two kinds of different metallic materials, can solve the problem of single material, which cannot meet the comprehensive properties such as high strength, high toughness, will have more and more application in all fields.In this paper, a new process of the liquid-solid compound casting was carried out to investigate the bimetal compound casting experiments of aluminum alloy and magnesium alloy by using a self-designed high vacuum liquid-solid composite device. The focus lies on surface treatment technology of different aluminum alloy, liquid-solid diffusion bonding process, microelement Sr and heat treatment process on the microstructure and mechanical properties of Mg/Al bimetal.1. Surface treatments of aluminium alloy have significantly improved the wetting and metallurgical bonding between the molten magnesium and aluminum substrate. The "zincate+galvanizing" process has been developed for aluminium alloy to remove the oxide layer on aluminum surfaces and replace it with a controlled thickness metallic zinc coating, to ensure a dense zinc coating preventing the re-oxidation of Al alloy surfaces. The results showed that the low melting-point Zn coating on aluminum substrates and the addition of Sr to molten magnesium both lead to exceptional wettability for the coated substrates, which would result in more metallurgical reactions in the interfacial regions.2. In AZ91/6061 bimetallic samples, no obvious defects were observed at the interfaces, indicating possible metallurgical bonding in these interfaces. The XRD patterns and EMPA results confirm the formation of Al12Mg17, Al3Mg2, α-Al and α-Mg phases in the interface. In this study, it was found that both primary α-Mg and the eutectic structure (Al12Mg17+α-Mg) were refined by the Sr modification. The shear strength of the AZ91D/6061 bimetallic samples were improved greatly with the additions of Sr. When the Sr content was about 0.3 wt.%, the AZ91D/6061 bimetallic sample obtained the optimal shear strength.3. For AZ31/A390 bimetallic compound casting technology, further investigation using SEM coupled with EDS sans showed the interfacial transition layer width was about 100-200μm, the microstructure in the interface were composed of a-Mg、 β-Al12Mg17 and Mg2Si phase. The results indicated that after adding trace amounts of Sr into the magnesium alloy, primary a-Mg in the interface of AZ31/A390 liquid-solid bonding was refined, and the continuous reticular β-Al12Mg17 became less and the volume fraction decreased. The shear strength of the AZ31/A390 bimetallic samples were improved greatly with the additions of Sr. After solution treatment at 420℃ for a holding time of 3h, and aging treatment at 165℃ for a holding time of 12h, the continuous Mg2Si phase in the interface was turned into fine spherical and dispersed particles. The shear strength of the interface was strengthened, and reached a peak value of 84.6MPa.