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Vacuum Heat Treatment Furnace

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Vacuum Brazing Furnace

METHOD OF BRAZING ALUMINUM TO STAINLESS

Aluminum alloy has a series of properties such as high specific strength, high specific stiffness, light weight, and corrosion resistance. Its application fields are constantly expanding, especially in automobile manufacturing and other industries. It has broad application prospects. However, compared with steel, aluminum alloys are more expensive and have poor weldability. Therefore, it is of great practical significance to realize reliable connection between aluminum alloy and steel, especially the connection with stainless steel. As we all know, the crystal structures, physical and chemical properties of Al and Fe are very different, resulting in poor weldability of aluminum alloys and stainless steel. This is reflected in the following: ① When Al and Fe interact, it is easy to form a series of intermetallic compounds such as FeAl₃, Fe₂Al₇, Fe₂Al₅ etc., these compounds make the joint brittle; ②The physical properties are quite different. The linear expansion coefficient of commonly used aluminum alloys is (23~27)x10^-6/C, and that of stainless steel is (12~18)x10^-6/C. The linear expansion coefficient is about 1 times larger than that of stainless steel, which can easily cause greater welding stress; ③AI has strong chemical activity, and it is easy to form a stable and dense oxide film on the surface of the material. At the same time, inclusions are produced due to oxidation during the welding process, which destroys the Continuity mesh of joints. It can be seen that it is extremely difficult to directly connect aluminum alloy and stainless steel using welding methods such as fusion welding. For this reason, this article chooses NiAg composite coating to connect 6063 aluminum alloy and stainless steel (1Cr18Ni9Ti) through contact reaction brazing, focusing on studying the structure of the brazed joint and the effect of the Ni plating layer on controlling the intermetallic compounds produced by A1 and Fe. In order to seek solutions to 6063 aluminum The welding of alloys and stainless steels will be explored to some extent.

Vacuum brazing operation steps

The two base materials of 6063 aluminum alloy and 1Cr18Ni9Ti steel are each processed into 15mmx15mmx2mm samples using wire cutting methods. The thickness of the Ni and Ag intermediate layers on the surface of the stainless steel is about 5μm and the thickness of Ag is about 10um using the brush plating method. Specific steps: polish the stainless steel surface to be locked → electro-clean → activate → Ni plating → clean → Ag plating. Welding is carried out in a vacuum brazing furnace, and the thermal vacuum degree is not less than 1×10-3Pa. The specimens were lapped and polished with metallographic sandpaper and cleaned with ultrasonic acetone before entering the furnace. Contact reaction brazing process parameters: temperature 580C, holding time 1, 5 and 20 minutes respectively. In order to prevent the specimen from moving during the welding process, a pressure of 0.1MPa was applied. The brazing heating rate is 45C/min, and the sample is cooled in the furnace after welding.

Vacuum brazing effect

(1) When the vacuum brazing time is short, the brazing seam structure shows that the 6063 aluminum alloy side is mainly composed of a eutectic structure composed of Al (Ag) solid solution and AgAl compounds, and the Ag-plated side is mainly composed of Ag-Al compounds. .

(2) When the vacuum brazing time exceeds 20 minutes, the Ag-Al compound content increases significantly, the Ni plating layer gradually disappears due to diffusion, and its effect on preventing the formation of Al-Fe brittle intermetallic compounds is weakened.