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Main characteristics of filler materials

The brazing alloys offered by LEGOR GROUP fall into five main categories based on their composition.

Silver based brazing alloys

Silver-based alloys are commonly used for general purpose brazing and are suitable to braze ferrous or non-ferrous materials (steel, copper, brass, nickel
etc.). These alloys are available in different compositions making them suitable for a wide variety of applications. When compared with iron-zinc alloys, the
presence of silver improves the fluidity of the alloy and its resistance to corrosion. There are two main categories: tin bearing and tin free alloys. The
presence of tin, at the same percentage of silver and zinc content, contributes in reducing the interval range of melting. The presence of zinc improves the
wetting properties of the ferrous materials. These alloys are cadmium free in compliance with the RoHS regulations. Silver based brazing alloys for special
applications are suitable for joining very hard materials like tungsten carbides or materials with low wetting properties such as molybdenum, chromium and
tantalum.

Copper based brazing alloys

Copper based alloys can be used to braze ferrous or non-ferrous materials (steel, copper, brass, nickel etc.). The presence of silicon improves the wetting properties through the elimination of oxides. Silicon also increases the resistance to oxidation and the mechanical resistance to high temperatures.
Copper based brazing alloys for special applications are suitable for joining very hard materials like tungsten carbides or materials with low wetting properties such as molybdenum , chromium and tantalum.

Copper-Phosphorous based brazing alloys

Copper-Phosphorous alloys are copper based filler metals that are selffluxing on copper by virtue of their phosphorous content. Copper alloys such as brass and bronze should be fluxed to assure a braze joint. These alloys cannot be used with materials containing sulphur, or with iron and nickel based substrates. There are two main categories: silver based and silver free alloys. The presence of phosphorous lowers the melting point, and facilitates the decomposition of the copper oxides. The phosphorous does not decompose the zinc oxides so in the case of brass brazing a flux is necessary.
Phosphorous can form brittle compounds with some metals (for example nickel and iron); the phosphides segregate at grain boundaries and cause intergranular embrittlement. The phosphorus-rich phase rapidly corrodes in presence of sulfur and the joint fails.

Gold based brazing alloys

These brazing alloys comply with the most stringent requirements imposed by many industries such as: Power Turbine, Aerospace, Semiconductor, Medical
and Electronic. Gold-copper based alloys offer good wetting properties on metals such as copper, nickel, cobalt, molybdenum, tantalum, niobium etc.
and a high capacity in filling narrow joint gaps. The gold-nickel based alloys have all the properties of the gold-copper ones. However the presence of
nickel offers higher mechanical and oxidation resistance. Gold-silver brazing alloys are available with or without indium which is used as a thermal
suppressant.

Palladium based brazing alloys

These brazing alloys comply with the most stringent requirements imposed by many industries such as: Power Turbine, Aerospace, Semiconductor, Medical
and Electronic. The main products are based on a ternary composition of palladium-silver-copper alloys containing between 5 and 25 %wt. of Pd; main
characteristics are narrow melting range and good oxidation resistance. When compared to silver based brazing alloys, these products present improved
mechanical properties in very high temperatures. These alloys confer excellent resistance to corrosion in many environmental conditions and offer excellent
flowing and filling properties.