Effect of cold rolling on aging precipitation behavior and mechanical properties of Cu–15Ni–8Sn alloy

Abstract

The present study investigated the aging precipitation behavior and mechanical, electrical properties of Cu–15Ni–8Sn alloy affected by cold rolling with different deformations. During cold rolling, the grain is elongated gradually along rolling direction with increasing deformation, simultaneously accompanied by the occurrence of a great deal of dislocations and deformation twins. During aging process, the coherent DO22 and L12 ordered phases precipitate successively from the matrix after 90% rolling deformation and aging treatment at 400 °C for 0.5 h with the orientation relationship of (1¯10)DO22 // (022¯)Cu, [111]DO22 // [211]Cu; (11¯1¯)L12// (11¯1¯)Cu, [211]L12 // [211]Cu. However, discontinuous precipitation (DP) behavior is significantly accelerated by prior cold rolling. On the one hand, by revealing the underlying growth kinetics of DP, it can be found that the nucleation sites of DP transform from grain edges to grain boundaries gradually with increasing rolling deformation. On the other hand, the nucleation sites and nucleation rate of DP can be enhanced greatly with increasing dislocation density. Furthermore, the interlamellar spacing of DP slightly increases and the morphology transforms from lamellar structure to bush-like structure gradually with increasing rolling deformation. In addition, the hardness, tensile strength and electrical conductivity are obviously improved while the peak aging time greatly shortens with increasing rolling deformation. The optimal combination of properties with a hardness of 409 HV, a yield strength of 1256 MPa, and an electrical conductivity of 7.5 %IACS can be obtained in the sample with 90% rolling deformation after aging treatment at 400 °C for 0.5 h. The corresponding strengthening mechanism and conductive mechanism were discussed. It can be discovered that the precipitation strengthening, dislocation strengthening and solid solution strengthening are believed to be the main strengthening mechanisms to enhance the alloy strength.