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Vacuum brazing of 5005 aluminum alloy and 1Cr18Ni9Ti

With the development of aviation, aerospace, automobile, machinery manufacturing and chemical industry, 5005 aluminum alloy has become one of the most widely used non-ferrous metal materials due to its low density, high thermal conductivity and electrical conductivity. However, due to the melting point of 5005 aluminum alloy 1Cr18Ni9Ti stainless steel has good corrosion resistance, high melting point and strength, excellent plastic toughness and Hot and cold processing performance. Therefore, realizing the connection of 5005 aluminum alloy and 1Cr18Ni9Ti stainless steel can make the connected components have the advantages of the above two materials and expand their application fields.

As we all know, Al and Fe are quite different in crystal structure, physical and chemical properties, etc., so there are certain difficulties in the connection of aluminum alloy and stainless steel, especially the oxide film on the surface of aluminum alloy and the difference in the linear expansion coefficient of the two base materials, which also increase connection difficulty. At present, the aluminum-steel dissimilar metal joining methods mainly include fusion welding, friction welding, vacuum brazing and so on. When fusion welding is used, the residual stress of the joint is large, the composition of the weld is uneven, and there are defects such as cracks and slag inclusions at the interface. The occurrence of the above conditions will have an adverse effect on the performance of the joint. Friction welding has strict requirements on the shape of the workpiece, and the assembly requirements are relatively high. The toughness of the joint is poor and it is prone to cracking. When vacuum brazing is used to join aluminum alloy and stainless steel, although a large number of intermetallic compounds are formed at the interface, which affects the strength of the joint, a joint with good performance can be obtained by controlling the solder composition and process conditions. In this paper, 5005 aluminum alloy and 1Cr18Ni9Ti stainless steel were vacuum brazed with A1-Si-Mg solder, and then the interface structure and formation mechanism of the joint were analyzed, and the influence of process parameters on the interface structure and shear strength of the joint was analyzed.

experiment method

The base metals used in the test are 1Cr18Ni9Ti stainless steel and 5005 aluminum alloy, and their chemical compositions are shown in Table 1 and Table 2, respectively. Before the test, 1Cr18Ni9Ti stainless steel and 5005 aluminum alloy were machined into 30 mm x 10 mm x 1.5 mm and 7 mm x7 mm x 5 mm samples respectively by wire cutting method. The solder used in the test is 150 um thick Al-Si-Mg foil solder, and its chemical composition is shown in Table 3.

Before vacuum brazing, use sandpaper to grind the surface of the base metal to be welded step by step, and use acetone solution to ultrasonically clean the base metal. In order to remove the oxide film on the aluminum alloy surface, ultrasonic alkaline cleaning with NaOH dilute solution is carried out at 40 °C , and then pickled with dilute HNO solution. In this paper, a SIMUWU vacuum brazing furnace was used for brazing experiments. The brazing temperature was 560-590 ℃, and the holding time was 5-25min. After welding, a scanning electron microscope (SEM, S-4007 ) to observe the interface structure and fracture morphology; use a rotating anode X-ray diffractometer (XRD , D/max-rb) to analyze the phase of the interface product to determine the reaction product; use INSTRON MODEL 5569 electronic universal testing machine to carry out the compression shear test .

in conclusion

(1) 5005 aluminum alloy and 1Cr18Ni9Ti stainless steel are brazed with Al-Si-Mg solder. When the vacuum brazing temperature is 580°C and the holding time is 15 min, the interface structure of the joint is 1Cr18Ni9Ti stainless steel/FeAl/FeAl3/FemAln+αAl /5005 aluminum alloy.

(2) When the vacuum brazing process parameters are low, there is residual oxide film on the surface of 5005 aluminum alloy, so there are obvious cracks or pore defects in the weld; when the vacuum brazing temperature rises to 580°C, the welding defects disappear and the weld When the vacuum brazing process parameters are further increased, due to excessive welding heat input, excessive interface reaction, high residual stress in the joint, and obvious cracks in the weld.

(3) With the increase of vacuum brazing temperature or the extension of holding time, the shear strength of joints shows a trend of first increasing and then decreasing. When the vacuum brazing temperature is 580 ℃ and the holding time is 15 min, the maximum shear strength of the joint is 49 MPa.

(4) The vacuum brazing temperature has a significant effect on the fracture position of the joint. When the vacuum brazing temperature is low, the joint fracture occurs at the FemAln + αAl reaction layer and the oxide film layer on the aluminum alloy side; when the vacuum brazing temperature rises to At 580 °C, the fracture occurred at the FemAln+ αAl reaction layer.