| Aluminum alloys have the properties of high specific strength, specific stiffness, light weight and corrosion resistance, while stainless steels have the properties of high strength, weldability and corrosion resistance. It is useful to bond aluminum alloy and stainless steel in the aerospace, automotive and chemical engineering, but is very difficult because of the difference on the crystal structure, physical and chemical properties of Al and Fe elements, especially of the existence of stable Al2O3 on the aluminum alloys. Therefore, the joining between aluminum alloys and stainless steel will be always focused on in industry.In this thesis, based on previous studies, the low temperature diffusion bonding between 6063 aluminum alloy and 1Cr18Ni9Ti stainless steel was studied with plating Cu, plating Ag and Al-Si films as the interlayer. The wettability, interpenetration at the grain boundary, and microstructure at the interface were observed with optical microscope, SEM, EMPA and XRD analysis. The mechanical properties of joints were tested, and the optimization of processing parameters was also done. With Al/Fe diffusion couple, the diffusion under different temperature and holding time were executed to study the diffusion between Al and Fe atoms, the mechanism on the growth of interfacial reactive layer, and the diffusion equation on the concentration of Al and Fe at the interface of joints.In the low temperature diffusion bonding between 6063 and 1Cr18Ni9Ti using plating Cu as the interlayer, the reactive and physical wetting produces a better wettability of Al-Cu liquidus at the surface of 6063 with the wetting angle lower than 10 degree. The microstructure at the interface includes 6063/Fe2A15+Fe3Al/AlCu+ AlCu4/eutectic structure of Al solid solution and Al-Cu intermetallics/1Cr18Ni9Ti stainless steel. With the brazing time increasing, the thickness of IMC layer increased, while the width of eutectic structure decreased at the interface. Calculation shows the penetration rate of Al-Cu liquidus into the grain boundary was 1.3297×10-8m/s, and the dissolution of Cu interlayer is a very short processing in seconds. The joint strength was about 83 MPa for a 10μm Cu interlayer under the diffusion temperature and time of 510℃and 30 min, respectively.In the low temperature diffusion bonding between 6063 and 1Cr18Ni9Ti using plating Ag as the interlayer, the microstructure at the interface includes 6063/Ag-rich phase/Al(Ag) solid solution and Ag-Al intermetallics/Ag-Al intermetallics/Fe-Al intermecallics/1Cr18Ni9Ti. Due to the diffusion path of Al atoms, the formation of Fe-Al intermetallics was later than that of other intermetallics, and so the growth of Fe-Al intermetallics was retarded by the Ag interlayer. Compared contact reactive brazing, low temperature diffusion bonding contributed a slow growth rate for Fe-Al intermetallics. The thickness of interfacial reactive layer was linear to square of the holding time, with the growing active energy of 162.39 KJ/mol.In the low temperature diffusion bonding between 6063 and 1Cr18Ni9Ti using Al-Si as the interlayer, the results show that the holding time had a lower effect on the wettability at the surface of 6063 than that at the surface of 1Cr18Ni9Ti. With a higher temperature and longer holding time, at the interface it will be shown a decreasing eutectic phase, but a growing eutectic Si and thickness of Fe-Al intermetallics, and even a crack at the interface. Correspondingly, the poor wettability and block brittle Si phases caused by the Fe-Al intermetallics and Al-Si eutectic liquidus at the interface will produce a joint with weak tensile strength.In the numerical analysis on the diffusion mechanism between Fe/Al couple, according to Boltzmann-Matano method, the relation equation of diffusion coefficient (D) and element concentration (C) of elements in interfacial transition zone was determined for Fe/Al diffusion couple. The diffusion coefficient of Fe and Al atoms in the interfacial transition zone can be obtained. The diffusion coefficient of Fe and Al atoms increased with the increase of the heating temperature and element concentration, and the diffusion capacity of Al atoms is larger than the one of Fe atoms in the interfacial transition zone. The reaction diffusion equation of elements in the interfacial transition zone can be obtained using diffusion coefficient and error function. The element concentration of Fe and Al atoms in the Fe3Al and AlCu4 intermetallics was calculated and compared with EMPA results. The consistence between them gave a reference on the future analysis on the Fe and Al atoms.Therefore, the main achievements in this thesis include the following three results. The low temperature diffusion bonding between 6063 aluminum alloy and 1Cr18Ni9Ti stainless steel can be obtained using a special interlayer, which destroys the oxide layer at the base materials and decreases the requirement on the surface preparation before brazing and the diffusion time during brazing. The penetration on the grain boundary and the formation mechanism of interfacial intermetallics were studied, in which the retardation on the formation of Fe-Al and Ag-Al and the restraint effect of plating Ni interlayer on the growth of Fe-Al intermetallics were observed. The element concentration of Al and Fe atoms in the interfacial transition zone based on Fick diffusion equation was created, which could be helpful to the prediction on formation of interfacial Fe-Al intermetallics and the optimization of brazing parameters.
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