Effect of Brazing Temperature on Microstructure and Mechanical Properties of Cu-Cr-Zr Alloy

Abstract:

Cu-Cr-Zr alloys are kinds of copper alloys with high strength and high conductivity, which usually apply to the manufacturing of key parts in complex environment such as high temperature and wear resistance. In this paper we studied the microstructure, tensile properties, microhardness, and fracture characteristics of Cu-1.04Cr-0.16Zr alloy at different brazing temperatures (600 ℃―800 ℃) by means of scanning electron microscope, cupping machine, micro-hardness tester, and stereomicroscope. On this basis, the softening mechanism of Cu-1.04Cr-0.16Zr alloy at high temperature was analyzed. The results showed that the ultimate tensile strength (UTS) and microhardness of alloys decreased with the increase of brazing temperature. The UTS , elongation, and microhardness of the samples were about 477.32 MPa, 40.13% and 151.78 HV. When the brazing temperature of Cu-1.04Cr-0.16Zr alloy was 600 ℃, the UTS decreased slightly whereas the microhardness was basically unchanged, and they showed good softening resistance. Partial recrystallization started to occur in the microstructure of Cu-1.04Cr-0.16Zr alloy when the brazing temperature was 650 ℃. Some fine and undistorted equiaxed grains appeared at the boundary of large equiaxed grains, which the grain size was about 2 μm―7 μm. The pinning effect of precipitation on grain boundary began to weaken, the UTS and microhardness decreased significantly. The samples were further softened with the increase of brazing temperature, a lot of annealing twins appeared in the microstructure of Cu-1.04Cr-0.16Zr alloy. Cu-1.04Cr-0.16Zr alloy had necking phenomenon and obvious plastic expansion zones after brazing. The shrinkage of cross section increased gradually with the increase of brazing temperature. The dimples grew along the tensile direction, and Cu-1.04Cr-0.16Zr alloy showed good plasticity. In summary, under the condition of satisfying the properties of the brazed joints, the softening of Cu-Cr-Zr alloys can be avoided by means of brazing filler metals with lower melting temperature.

Key words:brazing; recrystallization; ultimate tensile strength; microhardness