Role of Phosphorus in Copper-Phos Brazing Alloys

Copper-phos brazing alloys are widely used for brazing copper-copper joints due to their excellent performance and inexpensive cost.

Copper (Cu) and phosphorus (P) are the main elements of the solder. Firstly, phosphorous can significantly decrease melting temperature of copper. And it gives the brazing alloy a self-fluxing property.

Hua Guang Welding Brazing Copper with Copper Phosphorus Alloy

Copper-phos brazing alloys may have different compositions and varied solid-liquid temperature intervals. The brazing alloys with wide melting temperature range are suitable to braze joints with wide or uneven clearance. On the other hand, brazing alloys with narrow melting range and good fluidity are appropriate for brazing narrow gaps. If the heating process is slow during brazing, brazing alloys with wide melting interval may show segregation tendency. Therefore, heating method should be considered carefully in the case.

Copper Phosphorus Brazing Alloys

The ISO 17672 standard classifies copper-phos brazing alloys precisely based on their level of phosphorus content.

· CuP 179 contains the lowest level of phosphorus. Compared to other products, it has the uppermost plasticity. However, it also has the largest solidification interval and mid-level fluidity. Hence, it is normally used to braze the joints with wide clearances (0.07 – 0.13mm).

· CuP 180 and CuP 181 have excellent fluidity under brazing temperature. They are best suited to fill narrow joints (0.03 – 0.07mm). As CuP 181 has higher phosphorus content than CuP 180, its fluidity is also higher under the same process temperature. This brazing alloy can be hot-extruded into wires. And, a small joint fillets may be formed by applying this class of brazing materials.

· Composition of CuP 182 is rather close to the eutectic point of Cu-P phase diagram, and has a relatively low melting temperature. With its excellent fluidity, it will be promising to braze joints with fairly small gaps. Resulting joint fillets are small when this class of brazing alloys is selected.