ã€China Aluminum Industry Network】 Aluminum alloys are known for their low density, excellent corrosion resistance, and good electrical and thermal conductivity. Replacing steel with aluminum in welded structures can significantly reduce the overall weight. While steel is well-known for its weldability and mechanical properties, aluminum-steel joints have become widely used in industries such as automotive and shipbuilding due to their combined advantages.
However, welding aluminum and steel presents significant challenges. The melting point of aluminum is around 660°C, which is about 700–900°C lower than that of steel. During the welding process, aluminum melts first while steel remains solid. This leads to uneven mixing in the molten pool, as the aluminum tends to float on top of the steel. As a result, the weld composition becomes non-uniform after cooling. Additionally, the difference in linear expansion coefficients between aluminum and steel can create high residual stresses, increasing the risk of weld cracking.
To achieve a reliable connection between aluminum and steel, it's essential to overcome the oxide layer on aluminum surfaces and minimize the formation of brittle intermetallic compounds at the interface. Several welding techniques have been developed for this purpose:
1. Pressure Welding: This method involves applying pressure (with or without heat) during the welding process to join materials. Common techniques include explosion welding, magnetic pulse welding, friction stir welding, and diffusion welding. These methods are effective but often limited by the size and shape of the workpieces, leading to lower production efficiency.
2. Melting Brazing: This approach combines the principles of welding and brazing. In this process, the aluminum alloy and the brazing material are melted and then solidify to form a joint, while the steel remains solid. The molten filler material is drawn into the gap via capillary action, and interdiffusion occurs between the liquid filler and the steel, resulting in a strong bond.
3. Braze Welding: Similar to melting brazing, this technique involves placing the brazing material in the joint gap and heating it until it melts. The base metals remain solid, and the molten filler fills the space, forming a strong connection upon solidification.
Among these methods, pressure welding and braze welding offer practical solutions for joining aluminum and steel. However, they often face limitations in terms of workpiece geometry and production speed. Flux brazing, particularly laser-assisted filling and brazing, provides better control over intermetallic compound formation. It offers advantages like low heat input, fast welding speed, and easy automation, making it ideal for producing high-quality, efficient welds with broad application potential.
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