Selection of Brazing Filler Metals
Introduction
Brazing is a versatile and cost effective method of joining metal components. It is used in a variety of applications, including automotive and aerospace manufacturing, electronics, optics, and medical devices. Brazing filler metals (BFMs) are a critical component of brazing and are available in many varieties, compositions, and forms. The right choice of BFM is essential to ensure a successful brazing joint and avoid costly failures.
Classification of Brazing Filler Metals
BFMs can be broadly categorized into four basic material classes: copper-based, nickel-based, silver-based, and aluminum-based. Copper-based BFMs are generally available in the form of copper-phosphorous, copper-silver, or copper-zinc alloys. Silver-based BFMs are most commonly available as silver-based eutectic alloys or silver-based braze welds. Nickel-based BFMs are typified by nickel-phosphorus and nickel-silicon alloys. Aluminum-based BFMs include aluminum-zinc and aluminum-copper alloys.
Each BFM class has its own unique characteristics, advantages, and disadvantages. Copper-based BFMs are relatively inexpensive and provide a good seal against leakage. However, they require a moderately high temperatures and have a lower strength than other BFM classes. Silver-based BFMs offer the highest strength and excellent corrosion resistance, but are significantly more expensive than copper-based or nickel-based BFMs. Nickel-based BFMs offer good strength and ductility at lower temperatures than silver-based BFMs, but may be prone to oxidation. Aluminum-based BFMs provide excellent thermal and electrical conductivity, but are prone to brittleness at high temperatures.
Selecting the Right Brazing Filler Metal
Selecting the most appropriate BFM for a given application depends on several factors, including the base material, desired joint characteristics, and cost. For example, when brazing copper components, copper-phosphorous BFMs are often favored due to their low cost and good thermal conductivity. Silver-based BFMs are best suited for brazing stainless steel or other corrosion-resistant components, while nickel-based BFMs are the preferred choice for aluminum components due to their relatively low brazing temperatures. Aluminum-based BFMs may be a better choice for components that require high electrical and thermal conductivity.
Conclusion
Brazing is a versatile and cost effective method of joining metal components. The right choice of BFM is essential for a successful brazing joint. BFMs can be broadly categorized into four basic material classes: copper-based, nickel-based, silver-based, and aluminum-based. Selecting the most appropriate BFM depends on several factors, including the base material, desired joint characteristics, and cost. Careful selection of BFM can help ensure a successful brazing joint and avoid costly failures.
