Practical aspects of discontinuous precipitation and dissolution

A method of grain refinement which does not require plastic deformation is discussed. The refinement is obtained by a carefully designed thermal treatment in which the discontinuous precipitation (DP) reaction is followed by a dissolution process. Two different mechanisms of refinement were identified based on the investigations performed on Al-22 at.% Zn and Ni-4 at.% Sn alloys. The first one is associated with holding the orientation relationship of the former DP process. Such a behaviour was observed in the Al-22 at.%o Zn alloy in which the grains are refined by a factor of 7-8. If the small grains are created via recrystallisation within the area previously covered by a DP cell, like in Ni-4 at.% Sn alloy, a refinement factor of 40 or even more can be obtained. (C) 2002 Elsevier Science B.V. All rights reserved.