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Achieving the Perfectly Brazed Joint: The Essential Role of Brazing Flux

Brazing plays an indispensable role across a wide array of industries, including HVAC, refrigeration, automotive, aerospace, military, and more. Because of its criticality, this process demands precision and a keen eye for detail to achieve a flawless and robust joint. At Mathure Metal Works, we recognize the critical importance of every step in the brazing process, including the care we need to take pre and post brazing. In this blog post, we explore the crucial role of brazing flux in ensuring the cleanliness and deoxidation of surfaces and surroundings that facilitates the creation of durable joints.



The Impact of Dust on Brazing

Dust comprises tiny particles that can originate from various sources, including environmental debris, manufacturing residues, or the breakdown of tools and materials used in the workspace. When dust settles on the surfaces meant for brazing, it acts as a physical barrier between the base metals and the filler metal. This barrier disrupts the necessary intimate contact needed for the filler metal to properly wet and spread across the base metals. Wetting is a critical phenomenon in brazing, referring to the ability of the liquid filler metal to spread over a solid base metal due to adhesive forces overcoming cohesive forces in the liquid. If the filler metal cannot adequately wet the base metals, it cannot form a strong bond. Therefore, dust can significantly hinder the flow of the filler metal, compromising the integrity and strength of the joint.


The Role of Oxides in Hindering Brazing

Oxides form on metal surfaces when the metal reacts with oxygen in the air, a process known as oxidation. This reaction is natural and can occur rapidly at room temperature for some metals, or more prominently when metals are heated, as in the brazing process. The formation of an oxide layer on a metal surface introduces several problems:

  • Barrier to Bonding: Oxides create a chemically and physically inert layer on the metal surface. This layer prevents the filler metal from coming into direct contact with the base metal, preventing a strong metallurgical bond and leading to a weak joint.

  • Impeding Wetting: As mentioned, wetting is crucial for the brazing process. As oxides are chemically more stable, formation of oxides reduces the reactivity of the base metal and hinder the interaction with the filler metal. The poor wetting of the filler metal due to oxides means it cannot flow into and fill the joint effectively, compromising the strength and integrity of the brazed joint.

  • Preventing Capillary Action: The presence of oxides can also interfere with the capillary action needed to draw the filler metal into the joint. Capillary action relies on the surface tension of the liquid filler metal and the adhesion between the liquid filler metal and the solid base metals. Oxides disrupt this delicate balance, preventing the filler metal from being drawn into the joint and creating voids or gaps within the joint, which weakens its mechanical properties.

Thus, for a brazing joint to be durable, the surfaces of the materials to be joined must be impeccably clean and free of oxides.


Selecting the Right Brazing Flux

The choice of brazing flux is pivotal and varies depending on the materials involved, the specific brazing technique employed, and the intended application of the joint. Mathure Metal Works has a range of fluxes that can cater to all the different requirements. Currently, the main flux categories are:

  • Borax-based fluxes: Ideal for copper and brass, creating a protective layer against oxides.

  • Aluminum-based fluxes: Targeted for aluminum alloys, these fluxes excel in removing the stubborn aluminum oxide layer.

  • Silver-based fluxes: Best suited for silver and precious metals, formulated to eliminate and prevent oxides effectively.


The appropriate use of brazing flux is not just critical; it's transformative in the brazing process. At Mathure Metal Works, we not only provide high-quality brazing fluxes but also partner with our clients to ensure their brazed joints are consistently exceptional. Our dedication to excellence and innovation in brazing solutions empowers our partners to achieve perfect joints every time, reinforcing the strength, reliability, and integrity of their projects. Explore our range and discover how the right brazing flux can elevate your brazing outcomes to the pinnacle of perfection.


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