certain copper - nickel - tin alloys falling within a single phase region at temperatures approaching the melting point , but within a two - phase region at room temperature , when pretreated to produce a supersaturated single phase structure having a medium to fine grain size , followed by cold working to at least 75 percent area reduction and concluding with a critical aging treatment determined by the alloy composition and by the extent of prior cold working , exhibit higher mechanical strengths for given levels of ductility than have heretofore been attained for copper alloys . the alloys of the invention are useful in a variety of applications requiring a combination of properties including mechanical strengths , ductility , electrical conductivity and corrosion resistance , and are particularly useful as springs , relay elements , wire connectors and other similar flexible articles .