A. Yousefiani et Fa. Mohamed, Correlation between former alpha boundary growth kinetics and superplasticflow in Zn-22 pct Al, MET MAT T A, 31(1), 2000, pp. 163-172
Former alpha boundaries (F alpha Bs) are residual grain boundaries that dev
elop in Zn-22 pet Al during a heat treatment, which is normally applied to
produce the fine structure necessary for micrograin superplasticity. They r
epresent domains consisting:of fine elongated alpha grains, which encompass
groups of fine alpha (Al-rich) and beta (Zn-rich) phases (the superplastic
microstructure). The results of a detailed investigation conducted on F al
pha B growth kinetics in five grades of Zn-22 pet Al with various impurity
contents reveal a direct correspondence between the level of impurities in
the alloy and the characteristics associated with F alpha Bs (average size
of F alpha Bs and the value of the F alpha B growth exponent). This corresp
ondence, which, according to available evidence, is the result of impurity
segregation at F alpha Bs, lends strong support to the interpretation of su
perplastic behavior at low stresses in terms of phenomena arising from boun
dary segregation. It is suggested that information on F alpha B growth kine
tics in Zn-22 pet Al can be utilized to predict the low-stress Superplastic
characteristics of the alloy, such as the existence of region I or the occ
urrence of extensive cavitation.