A common use for RWMA Class 20 material is spot welding of galvanized steel. Its properties of anti-sticking and heat resistance have made it one of the choices for this sometimes difficult welding operation. These good properties do come at a premium over other materials with similar properties.
The problem encountered when welding galvanized is that the zinc/galvanized coating readily alloys with the copper of the electrode and weakens its surface structure and forms a layer of brass on the welding surface. Any alloy which maintains its strength and retards this surface condition is a candidate for galvanized welding. Class 20 dispersion strengthened copper is a good candidate but not the only one.
RWMA Class 2 chromium copper is another alloy often used to spot weld galvanized. Its hardness and electrical conductivity are virtually the same as Class 20. With these properties it can function in the same welding environment and perform the same functions without a material premium charge.
RWMA Class 1 zirconium copper also has great electrical conductivity and good hardness and finds good success spot welding galvanized materials without a material premium.
Both Class 1& 2 can be substituted for Class 20 for welding galvanized material. In fact, Class 1 & 2 are the biggest users in the galvanized resistance welding marketplace and are stocked in most rod, bar and electrode sizes.
Substituting one electrode alloy for another may require adjustments to the weld schedule. Pressure, current and time (PCT) are the variables that could be adjusted. This may lead to requalification of the weld set-up depending upon your in house procedures and the amount of the schedule change.
Reference: RWMA Resistance Welding Manual 4th Edition
AWS J1.3 Specifications for Materials Used in Resistance Welding electrodes and Tooling