The welding method of steel and aluminum is very poor, not only the melting point of the two is quite different.  The melting point of steel is about 1350℃, while the melting point of aluminum is about 660℃. Density also varies widely: about 7.87t/m3 for steel and 2.70t/m3 for aluminum. Moreover, the aluminum surface is prone to forming refractory oxide film.  Which prevents the combination of the two. Aluminum and iron can form brittle intermetallic compounds. Which are easy to cause deformation and crack. The gas welding process of steel and aluminum is essentially “braze-fusion welding”. That is, the steel side is brazing and the aluminum side is fusion welding. Temperature control during gas welding can avoid brittle structure and obtain good joint.

Gas welding  method of stainless steel and aluminum (1)

Because stainless steel direct gas welding is difficult, so take the first hanging on stainless steel silver. That is, the use of transition layer, and then aluminum welding method. The specific welding process is as follows.

(1) Before welding cleaning, first welding parts with acetone. Alcohol or gasoline to oil. And then chemical cleaning. The welding parts of the stainless steel parts were immersed in the aqueous solution of 30% nitric acid.  3% sodium chloride and 3% sodium fluoride.  After taking them out for 0.5 ~ 1h, they were immersed in the aqueous solution of 40% nitric acid and 10% potassium dichromate. And passivated for 0.5 ~ 1h. After taking them out, they were cleaned and dried with water.

The welding parts and welding wires of aluminum parts were immersed in 15% sodium hydroxide solution for 5 ~ 10min. And the sodium hydroxide acted with alumina to generate soluble aluminum hydroxide. Which was taken out and cleaned with water. Then it was immersed in 20% nitric acid solution and neutralized for 2 ~ 3min.  After removal, it was cleaned and dried with water.

Gas welding  method of stainless steel and aluminum (2)

2) welding process, slightly carbonized flame as the welding flame. Heat the welding part of stainless steel to about 300℃; And then feed HL303(silver solder) end also heated to the same temperature;  Coated with flux 102, coated to the welding place;  Continue to heat the welding piece to 600 ~ 700℃, and fill HL303, until the welding layer thickness up to 0.3mm.  The welding piece temperature at 500 ~ 600℃;  Put the aluminum piece on the welding place;  Heat the aluminum piece and the wire 301 end to 300 ~ 400℃ with neutral flame, and weld the wire 301 with gas agent 401.

During the operation, it is necessary to pay attention to the even action of the welding wire.  And fill the welding pool to keep the metal in the pool from being oxidized. Eliminate the gas, oxide and other sundries in the welding pool. And avoid the pores and cracks in the welding seam. Welding shall be continuous, preferably in one pass, and shall be as quick as possible.

(3) clean up after welding, carefully wash the joint with a bristle brush in hot water. And then soak the joint in a solution of chromic anhydride or potassium dichromate with a temperature of 80℃ and concentration of 2% ~ 3% for about 3 ~ 5min;  Carefully wash the joint with a bristle brush, then wash it in hot water, and finally dry it.

Gas welding method of carbon steel and aluminum

Before welding, clean the place where the welding parts are to be welded and weld according to the method of aluminum gas welding. Only one side of the aluminum is melted. The long welding seam should be segmented-welded with the joint strength up to 75MPa.

Other welding method

Steel and aluminum can also be used argon arc welding; Pressure welding;  Brazing, friction welding; Electron beam welding and other methods.