ã€China Aluminum Industry Network】 Aluminum alloys have excellent properties such as low density, good corrosion resistance, electrical conductivity and thermal conductivity. Using aluminum alloys instead of steel can greatly reduce the quality of welded structures. The steel has good weldability and mechanical properties, and the aluminum-steel welded structure has been widely used in automobiles, shipbuilding and other industries.
The melting point of aluminum is 660°C, which is 700-900°C lower than that of steel. When welding, the aluminum with low melting point melts first. At this moment, the steel is still not melted. Due to the great difference between aluminum and steel, the aluminum in the molten pool floats. On the top of the steel, the composition of the weld will not be uniform after cooling; the difference in linear expansion coefficient between aluminum and steel will cause a large residual stress in the welded joint, resulting in weld cracking.
In order to realize the reliable connection of the aluminum-steel, it is necessary to overcome the hindrance of the connection of the oxide film on the surface of the aluminum and the aluminum alloy and to prevent the brittle intermetallic compound from being generated or reduced at the interface between the aluminum alloy and the steel. The existing welding methods are:
1. Pressure welding Pressure welding is the method of applying pressure (heated or not) to the weldment during welding to complete the weld. When welding aluminum and steel, commonly used explosion welding, magnetic pulse welding, friction stir welding, diffusion welding and other methods.
2. Melting brazing Aluminium-steel dissimilar materials are brazed together with the characteristics of welding and brazing. In the welding process, the aluminum alloy and the brazing material are melted and combined together after condensation to form a welded joint. The steel is not melted. The molten solder is sucked into and fills the gap of the solid weldment by means of capillary action. The liquid solder and the steel interdiffusion and dissolution, and the solid brazing joint is formed after condensation, and the connection between the aluminum alloy and the steel dissimilar metal can be realized.
3. Brazing of brazed aluminum-steel dissimilar materials is to place the brazing material in the joint gap of the weldment and melt it by heating, while the base metal does not melt, and the liquid brazing material penetrates into the gap of the solid weldment and cools. After solidification it forms a firm connection.
In the welding method of three kinds of aluminum-steel dissimilar materials, pressure welding and brazing process methods can realize the connection of aluminum steel, but the size and shape of the workpiece are limited, and the production efficiency is low. Flux brazing can control the intermetallic brittle compounds of aluminum steels through brazing materials, especially laser filling and brazing. It has the characteristics of small heat input, fast welding speed and easy automation. It can obtain high-quality, high-efficiency fusion brazing welding joints. Wide application prospects.
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