When welding copper in a high electrical conductivity situation, it’s best to know the physical and chemical properties so you know what’s needed in a welding alloy. The differences in electrical conductivity between a welding alloy and the copper base metal can be extreme, even when the alloy is 98% copper.
Oxygen free copper (CDA10100) is used more times than not in high electrical situations. This alloy provides 102% IACS electrical conductivity of copper. Deoxidized copper (CDA18900) is a high copper welding alloy which provides 42% IACS electrical conductivity of copper. The difference in copper content between the CDA10100 and CDA 18900 is minimal. Oxygen free copper contains 99.99% copper, deoxidized copper contains 98.0% copper. The other 2% of elements in CDA18900 are silicon, tin and manganese. These three elements don’t provide good electrical conductivity properties.
When electrical conductivity is not an issue, Silicon bronze, Aluminum bronze or Phosphorus bronze are all excellent choices as alloys for welding copper, brass or bronze.
The Copper Development Association (CDA) is a great resource to use to determine physical and chemical properties. You can find the CDA website at http://www.copper.org/.