Microstructural Changes in As-Cast 7475 Al Alloy during Warm Sever Forging
Microstructural changes taking place in an as-cast coarse-grained 7475 Al alloy was studied by using multidirectional forging (MDF) at a temperature of 250oC and at a strain rate of 3 × 10-4 s-1. The samples were deformed by MDF with a strain of 0.7 per pass up to cumulative strain (Σε) of 8.4. In the earlier stages of deformation, microstructural changes are mainly characterized by development of dislocation subboundaries with low-to-moderate misorientation angles. The misorientation angle initially increases with straining and reaches a plateau of around 3.7o in the strain range from 0.7 to 2.1, where new grain formation scarcely takes place in the original grain interiors. With further straining, grain fragmentation starts to occur accompanying with deformation bands developed at various directions, followed by rapid evolution of a new fine grain structure at large strain. The average grain size is around 1 μm at large strains and the average misorientation angle approaches a value of about 25o at Σε = 8.4.
T. Chandra, K. Tsuzaki, M. Militzer , C. Ravindran
A. Goloborodko et al., "Microstructural Changes in As-Cast 7475 Al Alloy during Warm Sever Forging", Materials Science Forum, Vols. 539-543, pp. 2922-2927, 2007