The Interface Reaction Between CoCrFeMnNi High Entropy Alloy With Molten Aluminum And The Study Of CMT Welding-brzaing

Currently, joining aluminum to steel is becoming a hot topic in the field of composite materials and making the engineering materials of low mass. However, bond dissimilar metals together is still a great challenge due to its huge differences in physical and chemical properties, and the tensile strength of the joint degraded seriously due to the brittle intermetallic compounds existed in the interface. Studies have shown that Co CrFeMnNi High Entropy Alloy（HEA）, as a single face-centered cubic（fcc） structure, can dissolve some Al in its structure and keep the original fcc structure in some extent. This provides a theoretical possibility for using the HEA as transition metal in joining aluminum to steel. According to the characteristics of the molten brazing, the experiment of as-cast high entropy alloy immersed into the molten aluminum was carried out. Phase structure, distribution, and its formation mechanism of reaction layer were investigated by XRD analyses, Scanning electron microscopy, Energy dispersive spectrometer, micro-hardness test and tensile test. Then 3mm sheets of 1060 aluminum and HEA were used as the base materials, ER4043 were employed as the filler metal. CMT welding process was carried out to achieve the weld-braze lap joint of 1060 /HEA, while the CMT weld-braze lap joints of aluminum alloy and stainless steel also produced after coating the surface of HEA with fixed flux（Nolock） which were taking as a control experiment. Macroscopic pattern, microstructures and mechanical properties were analysed.When HEA immers in the molten aluminum, complex intermetallics layer formed in the reaction interface which consist of Al₈₆Cr_13.5Fe_6.5, Al₈₆Mn₁₄, Al₃ Ni and Al₉Co₂. In addition,massive bulk Al-Cr-Mn intermetallics, platelike and retiform Al-rich phase which contains relatively higher amounts of Fe and Ni are found adjacent to the reaction layer. At the beginning of the hot dipping,the formation of the reaction layer is controlled by HEA atomic diffusion reaction and disembedding, the formation rate of reaction layer and the block phase located in Al side is very fast during the time. After the formation of the reaction layer, the thickness increases with the hot-dipping times. The thickness of the compound layers increased as a parabolic cure rule in 10 minutes. When the reaction time is longer than 10 minutes, thickness of intermetallics is increase to 20μm, the growth rate of intermetallics become slack. Heat preservation time and cooling rate, as well as the reaction temperature have obvious influence on phase distribution by controlling the diffusion amount of high entropy alloys element.The CMT welding brazing of HEA and 1060 aluminum results show that with the increase of wire feed speed, macro morphology of joints is getting better and better. Besides, special flux（Nolock） can make the melt easyer to spread out on the surface of high entropy alloys.There is a uniform reaction layer in the faying face which is consisted of Al₅₅Mn₂₀Si₂₅,Al_3.21Si_0.4 beside the rich aluminium intermetallic compounds compare with the hot-dipping test. With the increase of wire feed speed, the thickness of reaction layer also increase. When the wire feed speed rate is 4m/min, there are lots of pores and inclusions exist in the interface,the quantity of defects decrease as the wire feed speed increase. The tensile shear test results show that the strength of joint with special flux have enormously improved than no special flux. When the wire feed speed rate of 4.5m/min, precoating solder joint strength up to70.8MPa, the thickness of reaction layer is 4.5μm.