Which factor is critical for achieving a strong brazed joint?

Achieving a strong brazed joint is fundamentally reliant on the cleanliness and preparation of the surfaces to be joined. Careful pre-braze cleaning and inspection ensure that the metal surfaces are free from contaminants such as oils, dirt, dust, or oxidation. These contaminants can interfere with the flow of the filler metal and its ability to adequately bond with the base metals, which is essential for forming a strong joint.

When the surfaces are properly cleaned, the filler metal can effectively wet and spread across the joint, creating a solid metallurgical bond upon cooling. Additionally, inspection during this stage allows for the identification of any defects or irregularities that could compromise the joint's integrity before the brazing process begins.

In contrast, other factors listed either do not contribute positively to a robust joint or may detract from it. For instance, the aesthetics of the filler metal are irrelevant to the joint's strength, and improper positioning of components can lead to gaps that prevent proper capillary action and flow of the filler metal. Lastly, excessive heat can result in overheating, which may damage the components or alter the properties of the filler metal and base materials, weakening the joint. Therefore, ensuring rigorous cleaning and inspection is key to the success of the brazing process.