What key factor can lead to joint failure during brazing?

In brazing, the cleanliness of the base metal surfaces plays a critical role in the quality and integrity of the joint. When base metals are not adequately cleaned before the brazing process, contaminants such as oxides, oils, and dirt can prevent proper wetting and adhesion of the filler metal. This lack of bonding at the joint can result in weak points, ultimately leading to joint failure. Ensuring that the surfaces are free from contaminants allows the filler metal to flow and adhere effectively, creating a strong and reliable joint.

Improper flux application, excessive filler metal, and correct heating technique are significant factors in the brazing process, but they do not inherently lead to joint failure as directly as insufficient cleaning of the base metals. Proper flux application is crucial to protect the joint from oxidation, while excessive filler can lead to unnecessary buildup rather than failure, and correct heating ensures that the filler metal properly melts and flows. However, without clean surfaces, all these efforts can be rendered ineffective, resulting in a compromised joint.