Aluminum alloy has excellent characteristics such as low density, good corrosion resistance, high electrical and thermal conductivity, and the use of aluminum alloy instead of steel can greatly reduce the quality of the welded structure. While steel has good weldability and mechanical properties, aluminum-steel welded structures have been widely used in industries such as automobiles and ships.
The melting point of aluminum is 660°C, which is 700-900°C lower than steel. During welding, aluminum with a lower melting point is melted first, while steel is still not melted. Due to the large difference in density between aluminum and steel, the aluminum in the molten pool will float. On steel, the composition of the weld will be uneven after cooling; the linear expansion coefficient between aluminum and steel is different, which will cause a large residual stress in the welded joint, which will lead to weld cracks.
In order to achieve a reliable aluminum-steel connection, it is necessary to overcome the obstructive effect of the oxide film on the surface of aluminum and aluminum alloy on the connection, and to prevent or reduce brittle intermetallic compounds at the interface between the aluminum alloy and the steel. The existing welding methods are:
1, pressure welding
Pressure welding is a method of applying pressure (heated or not) to the weldment during the welding process to complete the welding. When welding aluminum and steel, methods such as explosive welding, magnetic pulse welding, friction stir welding, and diffusion welding are commonly used.
2, welding brazing
Aluminum-steel dissimilar material fusion brazing has the characteristics of fusion welding and brazing at the same time. During the welding process, the aluminum alloy and the brazing filler metal are melted and combined after condensation to form a fusion welded joint; while the steel is not melted, the molten brazing filler metal uses The capillary action is sucked and filled into the gap of the solid weldment, the liquid solder and the steel diffuse and dissolve each other, and form a firm brazed joint after condensation, which can realize the connection of aluminum alloy and steel dissimilar metals.
The brazing of aluminum-steel dissimilar materials is to place the solder in the joint gap of the weldment, and melt it by heating, but the base material does not melt, and the liquid solder penetrates into the gap of the solid weldment, and it is formed after cooling and solidification. Strong connection.
Among the three welding methods of aluminum-steel dissimilar materials, the pressure welding and brazing process methods can realize the connection of aluminum and steel, but there are certain restrictions on the size and shape of the workpiece, and the production efficiency is low. Fusion brazing can control the brittle compound between aluminum and steel through brazing filler metal, especially laser filler wire welding brazing, which has the characteristics of low heat input, fast welding speed, and easy to realize automation. It can obtain high-quality and high-efficiency fusion brazing welded joints. The application prospect is broad.