Al Eutectoid Research Articles

Evidence for cavitation in superplastic Zn-22 pct Ai of very high purity

The cavity formation of very high purity Zn--22% Al was studied. Results confirm that cavities are nucleated in the Zn--22% Al eutectoid during superplastic deformation, and the extent of cavitation is essentially identical to an alloy of commercial purity (190 ppm impurities). (FS)

Factors influencing ductility in the superplastic Zn-22 Pct Al eutectoid

The maximum attainable ductility in the superplastic Zn-22 pct Al eutectoid depends critically on the imposed strain rate, the testing temperature, and the initial grain size. High ductilities are observed at intermediate strain rates, and there is a decrease at both higher and lower rates of strain. It is shown that i) the maximum ductility occurs at higher strain rates as the temperature is increased and/or the initial grain size is decreased, and ii) the maximum attainable ductility increases with increasing temperature and/or decreasing initial grain size. For specimens tested at different temperatures, similar macroscopic fracture characteristics are observed in specimens exhibiting a similar maximum flow stress. The experimental trends are qualitatively explained by relating maximum ductility to the maximum strain rate sensitivity and examining the influence of cavitation on the time to rupture.

The influence of strain rate on ductility in the superplastic Zn–22% Al eutectoid

Abstract There is an optimum range of strain rate for maximum ductility in the superplastic Zn–22% Al eutectoid, and the elongation at fracture decreases at both low and high strain rates. For a testing temperature of 473 K and a grain size of 2·5 μm, tensile specimens deform to strains in excess of 2000% over almost two orders of magnitude of strain rate.

亜鉛・アルミニウム共析合金の高温引張りにおけるひげ結晶の生長

A typical superplastic alloy, fine-grained Zn-22 wt%Al eutectoid, was strained at elevated temperatures in a 500 kV electron microscope in order to understand the mechanism of apparently “superplastic” elongation of zinc-rich grains.Superplasticity is generally thought as a grain boundary phenomenon and not as the elongation of individual grains. Thus, the unusual elongation of zinc-rich grains was a puzzling feature of the deformation in favor of the grain deformation as the cause of superplasticity. The “in situ” observation proved that the elongated grain in fact grew at the grain boundary under the influence of the applied tensile stress. The growth rate is determined by the diffusion of zinc through the grain boundary. The apparently superplastic elongation was a diffusional creep that prevails when bulk super-plasticity is prohibited due to the thin foil geometry.The phenomenon is not only important the for elucidation of the mechanism but also is interesting as a process to grow whiskers.

The Effect of Processing History on Superplasticity in the Zn–Al Eutectoid Alloy

The Effect of Processing History on Superplasticity in the Zn–Al Eutectoid Alloy

The influence of copper additions on the superplastic forming behaviour of the ZnAl eutectoid

Measurements of the flow stress ( σ f ) and strain-rate sensitivity ( m) over a wide range of strain rates (ε) and at temperatures between 20°C and 300°C have been made on a range of SP alloys, basically the ZnAl eutectoid, (78 Zn-22 Al) but with additions of copper up to 1·0%, see Table 1. These additions do not significantly affect σ f or m above about 150°C. Again, the peak in the m vs. ε curve is not displaced by these copper additions above about 150°C. The creep rate at room temperature decreases with increasing copper content and varies by a factor of about 140 between 0 and 1·0% copper. An empirical vacuum-forming test shows that copper at these concentrations has no effect on the vacuum-forming time at 250–260°C.