Group A material is a designation of the Resistance Welding Manufacturers Alliance (RWMA). It describes a group of copper alloys with high strength and high electrical conductivity. Their properties make them excellent materials to use in the resistance welding industry as electrodes and current carrying componenets used in the machinery of the resistance welding industry.
RWMA has subdivided the Group A into four Classes 1-4. Each class has different electrical nad mechanical properties to fit the various requirements of the resistance welding industry.
The product description, properties and applications of these classes can be found in the Resistance Welding Manual - section 18-3, available at RWMA/AWS.
Reference: RWMA: RWMA Manual, 4th Edition