Overview of Steel/Aluminum Welding Technology

With the development of automobile lightweighting, aluminum alloys are increasingly used in automobiles, and steel-aluminum hybrid bodies and multi-material bodies are becoming important development directions. The ensuing problem of connecting steel and aluminum dissimilar materials has also received more and more attention and has become one of the key issues in the field of automotive lightweighting.

At present, the main methods of connecting steel and aluminum in the automotive industry are glued, riveted, and glue-riveted composite connections. However, compared with welding, mechanical connection still has disadvantages in some aspects. For example, the extensive use of rivets increases the weight of the connection joint, the mechanical connection of high-strength steel is more difficult, and it affects the mechanical properties of the connected materials (such as elongation). etc.) have higher requirements, etc. Therefore, a large amount of research work has focused on steel/aluminum welding technology.

The physical and chemical properties of steel and aluminum are very different, which leads to the following problems in the welding of steel/aluminum dissimilar metals:

(1) The melting points of steel and aluminum alloys are nearly 900°C different, the density is nearly three times different, and the linear expansion coefficient and thermal conductivity are 

quite different. During the welding process, the volume of the joint changes greatly, and defects such as shrinkage cavities and pores are easily formed. At the same time, large residual 

stress is formed, which deteriorates the joint performance;

(2) The solubility between steel and aluminum is small, and the steel/aluminum dissimilar metal welding interface will form brittle intermetallic compounds, such as FeAl3, Fe2Al5, FeAl2, etc.

These compounds will significantly reduce the mechanical properties of the joint, and at the same time, the residual stress will Cracks are easily formed under the action, leading to 

connection failure;

(3) There is a dense oxide film on the surface of the aluminum plate, which increases the contact resistance at the interface and limits thermal efficiency; at the same time, the oxide film can

easily become an expansion path for low-energy cracks, form welding defects, and affect the mechanical properties of the joint;

(4) The electrochemical properties of steel and aluminum alloys are very different, and there is a greater tendency of corrosion in the welding of steel/aluminum dissimilar metals.

In response to the above problems, experts and scholars at home and abroad have carried out a lot of research on steel/aluminum welding using laser welding, resistance spot welding, arc welding, friction stir welding, plug riveting and other welding methods. Through process optimization and new welding Process development, etc., have made certain progress. However, the brittle intermetallic compounds formed at the steel/aluminum welding interface and their impact on joint performance still require a lot of exploration. The corrosion problem of steel/aluminum welded joints also needs in-depth research to promote the engineering application of steel/aluminum welding. Lay the foundation.