Resoftening and Resistivity Variations in Thermally Deformed Cu-Sn and Cu-Sn-Zn Alloys

Resistometric and tensile characteristics were studied for both Cu-Sn
and Cu-Sn-Zn alloys in the temperature range from 573 K to 773 K. Resistivity
saturation was found to take place through two annealing stages. The time
exponent n for ε-precipitate dissolution during annealing within stage I in Cu-
Sn alloy and stages I and II for Cu-Sn-Zn alloy decreased with increasing
working temperature. The values of the rate constant K increased with
increasing deformation temperature. A softening behaviour was observed at
higher stresses and temperatures. This was deduced from both the decreasing
values of the strength parameters σy, σσf, χ, Y with increasing temperature and
the sharp change in strain hardening at the critical stress σc . Above σc, the
second hardening stage behaviour appeared during tensile testing. The results
were explained in view of the mode of dislocation interaction with both the
lattice defects and the different inclusions existing in the matrix. The associated
atomic rearrangement and the formation of deformation twins, thermally
activated by 0.24 eV in Cu-Sn alloy and 0.28 eV in Cu-Sn-Zn alloy, were also
considered.