Why is flux important in preventing oxidation during brazing?

• A. It chemically reduces oxides and protects the hot joint from forming new oxides as the filler metal flows
• B. It strengthens the joint by chemical bonding
• C. It lowers the melting temperature of the base metal
• D. It accelerates cooling of the joint

Answer: (B)

Flux's job is to prevent oxidation during brazing by cleaning and protecting the joint surfaces as the filler metal flows. It does this by chemically reducing existing oxides on the metal surfaces and forming a protective layer that keeps the hot surfaces from forming new oxides while the filler metal wets and fills the joint. This oxide-free surface allows the molten braze to spread by capillary action and create a sound metallurgical bond. Flux does not strengthen the joint through chemical bonding itself, nor does it change the base metal’s melting temperature or speed up cooling; those outcomes come from the braze metal and processing, not the flux.