Aluminum Braze Sheet
Brazing Sheet from United Aluminum
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Brazing / Brazing Sheet
Some aluminum sheet products are made up of a strong core alloy that is clad with a thin layer of high-silicon alloy which has a much lower melting point than the core. This allows a complex shape, such as a car radiator, to be fabricated then heated to a temperature that is sufficient to melt the cladding while leaving the core intact. The skin of oxide film that covers the surface of aluminum needs to be removed for effective brazing. There are three common brazing methods:
The component is immersed in a molten salt which acts as a flux as well as a heat source for melting the clad layer. The fluxes are corrosive and all traces must be removed after brazing.
Controlled Atmosphere Brazing
Sometimes also described by the trade name “Nocolok”, this process uses a non-corrosive powdered flux and an inert gas atmosphere.
Components are heated in a high vacuum, completely free of oxygen. The clad alloy must contain magnesium as an alloying addition. At the brazing temperature, the heat and vacuum causes the magnesium to “boil” out of the molten metal thereby breaking up the brittle oxide skin into small, harmless shards.