Plastic deformation of Al-4.5 wt% Cu and Al-4.5 wt% Cu-0.1 wt% In alloys under the effect of cyclic stress reduction (original) (raw)
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Journal of Materials Science, 1985
The instantaneous strains resulting from stress changes during steady state creep of polycrystalline aluminium and an AI-4.2 at % Mg alloy in the temperature range 100 to 300 ~ C, have been determined. Instantaneous plastic strains were found in both materials for stress increments and decrements. For polycrystalline aluminium the instantaneous plastic strain on a stress increment, Ae(+), was considerably larger than the instananeous strain on a stress increment, A e (-), whereas for A I-4.2 at % Mg A e (+) was approximately equal to Ae(-). Work hardening rates determined from Ae(+) and Ae(-,) for polycrystalline aluminium vary from about one-tenth to one-half of Young's modulus and depend strongly on temperature and stress. The need to improve existing creep theories to include both climb (recovery) and glide components is suggested.
Plastic deformation of aluminum under repeated loading
Metallurgical Transactions A, 1975
The plastic deformation behavior of high purity (99.999 pct) polycrystalline and single crystal aluminum under repeated stressing was investigated by studying the creep behavior. The creep behavior under repeated stressing (cyclic creep) was compared with the static creep behavior at identical peak stresses. The influence of such experimental variables as the applied stress, the amplitude of cyclic stress, the test temperature and the static creep rate prior to stress cycling were systematically examined. The most important experimental observation in this study was that the cycling of the creep stress could either enhance or retard the creep deformation, depending upon the combination of the experimental variables. The experimental variable that had the most significant influence on the cyclic creep behavior was the applied stress; the enhancement of the creep rate was observed above a threshold stress, while the cyclic stress retarded the creep deformation at lower stresses. The threshold stress was found to depend sensitively on temperature. The implications of the threshold stress were examined by an analysis of the work-hardening behavior.
Creep and ductility in an Al-Cu solid-solution alloy
Metallurgical Transactions A, 1987
High-temperature creep was investigated in an A1-3 wt pct Cu alloy at temperatures in the range of 773 to 853 K and at a normalized shear stress range extending from 10 5 to 7 x 10 -4. The results show the presence of three distinct regions. In region I (low stresses), the stress exponent is 4.5 and the activation energy is 155 kJ/mole. In region II (intermediate stresses), the stress exponent is 3.2 and the activation energy is 151 kJ/mole. In region III (high stresses), the stress exponent is 4.5 and the activation energy is 205 kJ/mole. Creep curves obtained in the three regions exhibit a normal primary stage, but the extent of the stage is less pronounced in region II than in regions I and III. The creep characteristics in regions I and II, along with the values of the transition stresses between the two regions, are in conformity with the prediction of the deformation criterion for solid-solution alloys. While the advent of region III (high stresses) correlates well with dislocation breakaway from a solute-atom atmosphere, the creep characteristics in this region are not entirely consistent with any of the existing high-stress creep mechanisms. The plot of elongation to fracture vs initial strain rate at 853 K exhibits two peaks at strain rates of 1 x 10 -4 and 6 x 10 -4 s -l. The first peak (1 x 10 -4 S -t) is attributed to the variation of the stress exponent for creep in the alloy with strain rate, and the second peak (6 x 10 -4 s -1) appears to reflect the effect of solute drag on dislocation velocity.
Constitutive description of high temperature creep in mechanically alloyed AlCO alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1994
Creep curves of four mechanically alloyed aluminum alloys were studied within the range of stresses from 20 to 180 MPa at temperatures of 623 and 723 K. Creep curves of pure aluminum at temperatures of 473-623 K were taken as reference material data. The curves were described by the McVetty equation. The primary and steady-state stages of creep can be interpreted as a result of changes in the internal stress following from competition between work hardening and recovery processes. The analysis makes it possible to divide the internal stress into two components, one being due to stress fields of dislocations and the other to the existence of dispersed particles. The latter component equals the threshold stress in steady-state creep.
Primary and secondary creep in aluminum alloys as a solid state transformation
Journal of Applied Physics, 2016
Despite the massive literature and the efforts devoted to understand the creep behavior of aluminum alloys, a full description of this phenomenon on the basis of microstructural parameters and experimental conditions is, at present, still missing. The analysis of creep is typically carried out in terms of the so-called steady or secondary creep regime. The present work offers an alternative view of the creep behavior based on the Orowan dislocation dynamics. Our approach considers primary and secondary creep together as solid state isothermal transformations, similar to recrystallization or precipitation phenomena. In this frame, it is shown that the Johnson-Mehl-Avrami-Kolmogorov equation, typically used to analyze these transformations, can also be employed to explain creep deformation. The description is fully compatible with present (empirical) models of steady state creep. We used creep curves of commercially pure Al and ingot AA6061 alloy at different temperatures and stresses to validate the proposed model. Published by AIP Publishing.
Deformation behavior of Al-Cu-Mg alloy during non-isothermal creep age forming process
Journal of Materials Processing Technology, 2018
Creep age forming process (CAF) has been developed for manufacture large aircraft components. Generally, in CAF, the component should experience heating, soaking and cooling stages. In order to acquire high precision of the creep-age formed components, the non-isothermal deformation behavior of Al-Cu-Mg alloy was investigated using the creep ageing, thermal expansion, hot tensile and creep age forming tests. During non-isothermal creep ageing process, both the elastic and thermal deformations grow in the heating stage. However, the elastic deformation drops to a certain degree and then the contraction occurs in the cooling stage. The non-isothermal creep deformation can be divided into six stages, in which the creep rate increases in the heating stage and decreases in the soaking and cooling stages. Under different applied stresses, the creep strain in the heating stage of the non-isothermal creep is about 22.28-26.86% of the total creep strain. Compared with the isothermal creep ageing process, steady-state creep rate of the non-isothermal creep ageing process is reduced. Nevertheless, total creep deformation in the non-isothermal creep ageing process is improved. Thus, the springback of the non-isothermal creep-age formed plate is smaller than that of the isothermal creep-age formed plate. It can be concluded that the creep behavior in non-isothermal conditions, particularly the heating stage, needs to be considered in CAF applications.
Creep behavior of an Al-2. 0 wt pct Li alloy in the temperature range 300 °C to 500 °C
Metallurgical Transactions A, 1993
The elevated temperature deformation behavior of an Al-2.0 wt pct Li alloy in the temperature range 300 °C to 500 °C was studied using constant extension-rate tension testing and constant true-stress creep testing under both isothermal and temperature cycling conditions. Optical microscopy and transmission electron microscopy (TEM) were employed to assess the effect of defonnation on microstructure. The data showed that the stress exponent, n, has a value of about 5.0 at temperatures above the a + oAlLi solvus (approximately 380 °C) and that subgrains form during plastic deformation. Models for dislocation-climb and dislocation-glide control of creep were analyzed for alloys deformed in the temperature range of stability of the terminal AlLi solid solution. A climb model was shown to describe closely the behavior of this material. Anomalous temperature dependence of the activation energy was observed in this same tem perature range. This anomalous behavior was ascribed to unusual temperature dependence of either the Young's modulus or the stacking fault energy, which may be associated, in turn, with a disorder-order transformation on cooling of the alloy.
SEVERE PLASTIC DEFORMATION OF Al ALLOYS
2013
Severe plastic deformation with self-recovery or post-deformation recovery has been frequently applied in the last two decades to manufacturing of nano-structured materials, inspired by the Hall-Petch relation between the strength of alloys and their grain size. Relatively soon was realized that natural limits occur imposed by the processed materials and it was early defined that ultimate grain refinement of single-phase alloys makes little sense as it leads to fast deterioration of properties or failure of the material due to dynamic release of energy stored in it. Therefore efforts were directed towards development of new compositions of multi-phase alloys in which dynamic recovery and recrystallisation processes could be hampered by precipitation. To study these processes with their adequate control, a working device was developed called MaxStrain, combined with Gleeble physical simulator. The MaxStrain uses two-directional deformation to reach accumulated strains of 50 and more,...