Welding of aluminum-steel dissimilar materials

Welding of aluminum-steel dissimilar materials

Aluminum alloy has excellent properties such as low density, good corrosion resistance, high electrical conductivity and thermal conductivity. Using aluminum alloy to replace steel can greatly reduce the quality of welded structures. Steel has good weldability and mechanical properties. Aluminum-steel welded structures have been widely used in automobile and shipbuilding industries.

The melting point of aluminum is 660℃, which is 700-900℃ lower than steel. During welding, aluminum with a low melting point melts first, while steel is still not melted. Due to the large difference in density between aluminum and steel, aluminum in the molten pool will float on the steel, which will cause uneven weld composition after cooling; the linear expansion coefficient between aluminum and steel is quite different, which will cause large residual stress in the weld joint and weld cracks.

Welding of aluminum-steel dissimilar materials

In order to achieve reliable connection between aluminum and steel, it is necessary to overcome the obstruction of the oxide film on the surface of aluminum and aluminum alloy to the connection, and to prevent or reduce the generation of brittle intermetallic compounds at the interface between aluminum alloy and steel. The existing welding methods are:

1. Pressure welding

Pressure welding is a method of applying pressure (heating or not) to the weldment during the welding process to complete the welding. When welding aluminum and steel, explosion welding, magnetic pulse welding, stir friction welding, diffusion welding and other methods are commonly used.

2. Melt brazing

Aluminum-steel dissimilar material melt brazing combines the characteristics of both fusion welding and brazing. During the welding process, the aluminum alloy and the brazing material melt, and after condensation, they are combined to form a fusion joint; while the steel is not melted, the molten brazing material is sucked and filled into the gap of the solid weldment by capillary action, and the liquid brazing material and steel diffuse and dissolve each other, and after condensation, a strong brazing joint is formed, which can realize the connection of aluminum alloy and steel dissimilar metals.

Aluminum alloy welding

3. Brazing

The brazing of aluminum-steel dissimilar materials is to place the brazing material in the gap of the weldment joint, melt it by heating, and the parent material does not melt. The liquid brazing material penetrates into the gap of the solid weldment, and forms a strong connection after cooling and solidification.

Among the three aluminum-steel dissimilar material welding methods, pressure welding and brazing process methods can achieve the connection of aluminum and steel, but they have certain limitations on the size and shape of the workpiece and low production efficiency. Melt brazing can control the brittle compounds between aluminum and steel metals through brazing filler metals, especially laser wire brazing, which has the characteristics of small heat input, fast welding speed, and easy automation. It can obtain high-quality and efficient melt brazing welded joints and has broad application prospects.