Superplasticity of aluminium alloys grain-refined by zirconium
TL;DR: In this article, the superplasticity of aluminium alloys containing magnesium, oint, iron and manganese as well as zirconium as a grain-refining addition element was investigated by high-temperature tensile tests.
Abstract: The superplasticity of aluminium alloys containing magnesium, oint, iron and manganese as well as zirconium as a grain-refining addition element was investigated by high-temperature tensile tests. The tool elongation and the strain rate sensitivity as a function of strain rate and temperature were determined. The activation enthalpy and activation volume were also determined in the superlastic region of the deformation. !n addition to the tensile tests metallo-graphic investigations were also made. The results obtained show that the superplasticity of the alloys investigated is increasing by the addition of iron but it is decreasing by the simultaneous addition of iron and manganese.
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TL;DR: In this article, the important benefits of ultrafine-grained (UFG) alloys for various applications stem from their enhanced superplastic properties, however, decreasing the temperature of super-plasticity and provid...
Abstract: The important benefits of ultrafine-grained (UFG) alloys for various applications stem from their enhanced superplastic properties. However, decreasing the temperature of superplasticity and provid...
16 citations
TL;DR: In this paper, the results of impression creep tests conducted on AlMgZn alloys are reported and the strain rate sensitivity and activation enthalpy were determined and the mechanical behaviour of the alloys as a function of the strain-rate sensitivity can be divided into three regions at low and high stresses.
Abstract: It is important for practical applications that some commercial alloys with stabilized finegrained structure should exhibit superplastic behaviour at high temperatures In this paper the results of impression creep tests conducted on AlMgZn alloys are reported and the strain rate sensitivity and activation enthalpy were determined The mechanical behaviour of the alloys as a function of the strain rate sensitivity can be divided into three regions At low and high stresses the strain rate sensitivity parameter is low and the deformation process is not superplastic Superplastic deformation takes place only at intermediate stresses The microstructural interpretation of these processes involves, in general, the change of the micromechanisms controlling the different deformation processes It was determined that by the supposition of a threshold stress depending strongly on temperature, the two regions due to low and intermediate stresses of the deformation can be described by the same constitutive equation
13 citations
TL;DR: In this article, the effect of copper and zirconium upon the high-temperature mechanical properties and the deformation mechanisms of Al-5.7 wt% Zn-2.0 wt % Mg alloys is studied.
Abstract: The effect of copper and zirconium upon the high-temperature mechanical properties and the deformation mechanisms of Al-5.7 wt% Zn-2.0 wt% Mg alloys is studied. Results of impression creep and tensile tests show that the addition of Cu increases the strength of the material, and strongly enhances dynamic recovery during high-temperature deformation. In the case of the ternary AlZnMg alloy the main rate-controlling process is viscous glide, but in the alloy containing 1.4 wt% addition of Cu the strain rate is controlled by dislocation climb (10 -6 s -1 < e < 10 -2 s -1 and 400 °C < T < 520 °C). The addition of 0.14 wt% Zr to the AlZnMgCu alloy results in a fine-grained microstructure due to which the material exhibits superplastic properties at high temperatures with grain boundary sliding as the dominant process during superplastic deformation.
10 citations
TL;DR: In this article, an Al-6%Cu-0.4%Zr alloy was processed by high-pressure torsion to produce an ultrafine-grained structure with a grain size of ~200nm at the steady-state level where the hardness remains constant with straining.
Abstract: An Al-6 %Cu-0.4 %Zr alloy was processed by high-pressure torsion to produce an ultrafine-grained structure with a grain size of ~200 nm at the steady-state level where the hardness remains constant with straining. Tensile testing showed that a maximum elongation of ~530 % was attained at 673 K with an initial strain rate of 1 × 10−3 s−1. Evaluation of the strain-rate sensitivity and the activation energy for the deformation confirmed that grain boundary sliding through grain boundary diffusion is the rate-controlling process for the superplastic deformation.
7 citations
TL;DR: In this paper, force-elongation and stress-strain curves have been analyzed for superplastically deformed alloys tested in uniaxial tension under constant cross-head velocity conditions.
Abstract: Force-elongation and stress-strain curves have been analysed for superplastically deformed alloys tested in uniaxial tension under constant cross-head velocity conditions. By considering instability criteria the curves can be divided into three characteristic stages. In the course of the first two stages the samples are work hardened while during the third stage no work hardening takes place, although 85 to 90% of the total deformation occurs at this stage. However, sometimes at the end of stage III a weak strain hardening appears again due to grain growth. From the analysis of stage III the strain-rate sensitivity can be determined in good agreement with other methods.
6 citations
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105 citations
TL;DR: The role of alloying additions in modifying the recrystallization behavior of aluminium alloys is discussed in this article, and possible deformation mechanisms in the newer alloys are discussed to demonstrate their relative importance.
Abstract: Although the phenomenon of super plasticity in metals was recognized for many years, the majority of alloys that were shown to be super plastic consisted of two phases present in approximately equal volumes. The only aluminium alloys known to be superplastic were of eutectic composition and did not, in general, possess other properties that would make them commercially attractive. More recently, superplasticity has been obtained in relatively dilute aluminium alloys with more useful user properties. A brief summary is given of the aluminium alloys of eutectic composition that have been shown to exhibit superplasticity, but the authors are mainly concerned with the newer, relatively dilute alloys. The roles of alloying additions in modifying the recrystallization behaviour, because of both their presence in precipitate particles and their influence in solid solution, are considered. Additionally, possible deformation mechanisms in the newer alloys are discussed to demonstrate the relative importanc...
57 citations
TL;DR: In this article, three methods are described for obtaining the activation energy for superplastic flow, which may be determined from tests performed either at constant strain rate or at constant stress.
Abstract: There is a unique activation energy for superplastic flow, which may be determined from tests performed either at constant strain rate or at constant stress. Three methods are described for obtaining the activation energy, and the procedures are illustrated using experimental data for the Zn–22% Al eutectoid alloy. It is shown that discrepancies in the published data cannot be attributed to differences in the activation energy under constant stress and constant strain rate conditions.
Fur Superplastizitat gibt es eine einzige Aktivierungsenergie, die in Experimenten bei konstanter Dehnungsgeschwindigkeit oder konstanter Belastung ermittelt werden kann. Zur Bestimmung der Aktivierungsenergie werden drei Methoden angegeben und anhand experimenteller Daten fur die eutektoidische Zn–22% Al-Legierung erlautert. Die Arbeit zeigt, das Diskrepanzen in den veroffentlichten Daten nicht auf Differenzen in der Aktivierungsenergie bei konstanter Belastung und konstanten Dehnungsbedingungen zuruckgefuhrt werden konnen.
43 citations
01 Jan 1972
40 citations
TL;DR: In this article, an Al-Zn-Mg alloy (7010) was cold-rolled and annealed to produce a small recrystallized grain size, and superplastically deformed in the temperature range 475 to 520° C at strain rates of 2.8×10−3 sec−1.
Abstract: An Al-Zn-Mg alloy (7010) was cold-rolled and annealed to produce a small recrystallized grain size, and superplastically deformed in the temperature range 475 to 520° C at strain rates
$$\dot \varepsilon = {\text{1}}{\text{.1 x 10}}^{{\text{ - 5}}} $$
to 2.8×10−3 sec−1. At 500° C and
$$\dot \varepsilon = {\text{2}}{\text{.8 x 10}}^{{\text{ - 5}}} $$
sec−1 superplastic elongations up to 350% were obtained, but above about 60% elongation the residual room-temperature tensile properties after heat treatment decreased due to increasing grain-boundary cavitation. Grain growth rates were increased by superplastic strain.
14 citations