Surface Alloying of Cupronickel Alloy with Aluminum using Tungsten Inert Gas Process

Surface melting and alloying of Copper-Nickel (Cupronickel) alloy by preplacing aluminum powder and using tungsten inert gas process (TIG) in shielded atmosphere of argon gas were investigated. Surface melting resulted in the formation of a fairly porous dendritic microstructure. Surface alloying with aluminum resulted in the formation of Al2Cu and Al4Cu9 intermetallic compounds along with Cu-rich matrix and unstable martensitic structure. Surface melting reduced the hardness from 140 HV0.1 (substrate) to 70 HV0.1, mainly due to the loss of cold work effect of the initial substrate. On the other hand, surface alloyed zone showed a hardness of 300 HV0.1, mainly due to the formation of intermetallic compound. Tafel polarization results indicated improvement in corrosion resistance of cupronickel alloy after surface melting and alloying.