M. Furukawa et al., STRUCTURAL EVOLUTION AND THE HALL-PETCH RELATIONSHIP IN AN AL-MG-LI-ZR ALLOY WITH ULTRA-FINE GRAIN-SIZE, Acta materialia, 45(11), 1997, pp. 4751-4757
Citations number
43
Categorie Soggetti
Material Science","Metallurgy & Metallurigical Engineering
Experiments were conducted on an Al-5.5% Mg-2.2% Li-0.12% Zr alloy to
investigate the feasibility of introducing an ultra-fine grain size us
ing equal-channel angular (EGA) pressing and of retaining an ultra-fin
e grain size at elevated temperatures. It is shown that ECA pressing i
s capable of reducing the grain size from an initial value of similar
to 400 mu m to a value of similar to 1.2 mu m. However, the microstruc
ture after ECA pressing is heterogeneous, with many areas of equiaxed
grains having high angle grain boundaries and some regions of subgrain
s with boundaries having low angles of misorientation. Unlike earlier
experiments on Al-Mg binary alloys, it is demonstrated that the grain
size of the Al-Mg-Li-Zr alloy is reasonably stable up to temperatures
as high as similar to 700 K because of the presence in the matrix of a
fine dispersion of beta'-Al3Zr precipitates. Microhardness data confi
rm the Hall-Petch relationship for grain sizes above similar to 2 mu m
produced by annealing at temperatures above similar to 673 K, but the
Hall-Petch relationship breaks down at smaller grain sizes because of
variations in the volume fraction of the delta'-Al3Li precipitates. (
C) 1997 Acta Metallurgica Inc.