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The reliable performance of electrical contacts often depends on the dimensional stability of the spring material used to operate these contacts. The fatigue and stressrelaxation behavior of two copper-base alloys, Copper Development Association Alloys 510 (5 percent tin phosphor bronze) and 725 (89%Cu-9%Ni-2%Sn), strengthened by thermomechanical processing has been investigated. Strengthening mechanisms resulting from a combination of cold work and low temperature heat treatment have been taken advantage cf to produce electromechanical spring materials which have good conductivity and corrosion resistance, have sufficient ductility forpunching and forming, are dimensionally stable for long periods of time and also adequately resist fatigue stressing. Test data are presented which show the materials processed in this manner to have significant advantages over currently available, commercial tempers in that they permit designs having higher working stresses and better material utilization, thus filling a need created by miniaturization.