Papers by Keyword: Age Hardening

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Authors: Benjamin Milkereit, Michael Reich, Olaf Kessler
Abstract: Quenching is a critical step during the strengthening age hardening of Aluminium alloys. To obtain optimal technological results, parts should be quenched with the upper critical cooling rate. The precipitation behaviour of Al alloys during cooling from solution annealing and thereby the critical cooling rates are typically investigated by in-situ measurements with differential scanning calorimetry (DSC). Conventional DSCs are limited at cooling rates below 10 Ks-1. Unfortunately, medium to high strength Al alloys typically have critical cooling rates between 10 and some 100 Ks-1. Recently it was shown that dilatometry is generally able for in-situ detection of precipitation in Al alloys. Dilatometry allows controlled cooling up to some 100 Ks-1 and therefore covers the cooling rate range relevant. In this work, we aim to show up and discuss possibilities and limitations of dilatometric detection of quench induced precipitates in 2xxx, and 7xxx Al alloys. The basic method will be presented and results will be compared with DSC work.
Authors: Yuhei Ebata, Mitsuaki Furui, Susumu Ikeno, Katsuya Sakakibara, Seiji Saikawa
Abstract: In this study, age-hardening behavior of Mg-Xmass%Al alloys (X=3, 4.5, 6, 7.5 and 9mass%) were investigated by Vickers hardness measurement and optical microscopic observation. Each alloy was solution-treated and then isothermal-aged at 473, 498 and 523K. In the case of aluminum content less than 6mass%, Mg-3mass%Al and Mg-4.5mass%Al alloys, occurred insignificant age hardening. In the case of aluminum content higher than 6mass%, Mg-6mass%Al, Mg-7.5mass%Al and Mg-9mass%Al alloys, occurred remarkable age hardening. For each aging temperature, with heighten aluminum content, increase the value of maximum hardness and shorten time to maximum hardness. Mean hardness of discontinuous precipitation during aging increased with lower aging temperature and higher aluminum content. Furthermore, over-aged microstructure of Mg-Al system alloys differed from aluminum content or aging temperature.
Authors: Seyed Ali Asghar Akbari Mousavi, S.H. Sham Abadi
Abstract: The effect of tool traverse and rotation speeds on the microstructures and mechanical properties are quantified for welds between non-age-hardening Al5083 and age hardening Al2024 and compared to single alloy joints made from each of the two constituents. In this paper, we report the results of microstructural, mechanical property investigations of Al5186Al2024 friction stir welds produced using various rotations and traveling speeds of the tool to investigate the effects of the welding parameters on the joint strength. Metallographic studies by optical microscopy, electron probe microscopy, and the utilization of the X-ray diffraction technique have been conducted. It was found that the weld properties were dominated by the thermal input rather than the mechanical deformation by the tool. In particular the larger stresses under the weld tool on the AA5186 side compared to the AA2024 side are related to a transient reduction in yield stress due to dissolution of the hardening precipitates during welding prior to natural aging after welding.
Authors: A. Dupasquier, Rafael Ferragut, M.M. Iglesias, C.E. Macchi, Mario Massazza, P. Mengucci, G. Riontino, Alberto Somoza
Authors: Vahid Fallah, Andreas Korinek, Babak Raeisinia, Mark Gallerneault, Shahrzad Esmaeili
Abstract: Al-Mg-Si-(Cu), i.e. AA6xxx, alloys are widely used light alloys which can be effectively strengthened through precipitation hardening. The final microstructure, and thus properties, of these alloys after common artificial aging treatments are largely determined by the composition-dependent nano-scale clustering and precipitation that occur during the earliest stage of aging. Therefore, multi-length scale analysis of the earliest-stage of precipitation can provide critical knowledge in understanding the basis for the microstructural evolution during aging and attaining the desired microstructures and properties. Here, we investigate the effect of alloy composition on the evolution of early-stage clusters and precipitates during aging at 180°C using high resolution transmission electron microscopy. The results map a sequential evolution of clusters with an FCC structure but different morphology/orientation characteristics. GP-zones with structures other than FCC, also form in the early stages of aging. The composition-dependent kinetics of β” phase precipitation and hardening behavior are discussed in light of the results from differential scanning calorimetry experiments, microhardness measurements, and conventional transmission electron microscopy.
Authors: K. Matsuda, S. Taniguchi, Kosuke Kido, Susumu Ikeno
Authors: Teruto Kanadani, Keiyu Nakagawa, Norio Hosokawa, Akira Sakakibara, Koji Murakami, Makoto Hino
Abstract: The aging of Al-Zn alloys has been vastly studied for decades. In the previous paper, 0hta et al. studied carefully the hardness of the alloy during aging and revealed the existence of softer regions near the surface and the grain boundary than the interior of the specimen even after aging for a long time. Electrical resistivity measurement and X-ray small angle scattering experiment together with hardness test suggested that in these regions vacancy decay to the surface and grain boundaries was severe, thus the growth of GP zones were suppressed and therefore age hardening was retarded. Also, it is well-known that an addition of a small amount of Ag raised solvus temperature of GP zones. In this paper, soft surface layer formed in an Al-12mass%Zn alloy is studied by adding small amount of Ag by means of hardness test and resistometry. Addition of Ag more than 0.1% decreases the thickness of soft surface layer as well as accelerates age hardening rate and suppresses the formation of soft region near the grain boundaries. Higher quenching temperature also reduces the thickness of soft surface layer. Together with the behavior of aging curves of the specimen with various thicknesses, the origin of the soft surface layer is confirmed to be the effective role of surface as sinks for vacancies.
Authors: Y. Oe, K. Matsuda, J. Nakamura, S. Ikeno
Abstract: The effect of Cu or Ag addition on 2 step aging in Al-Mg-Si alloy has been investigated to understand precipitation for this alloy. The maximum hardness of two step aged alloy was higher with increasing pre-aging time for Al-Mg-Si alloy. There was no remarkable difference between the peak-hardness of the Ag addition alloy with and without pre-aging. The hardness decreased once for the Ag addition alloy aged at 473K just after pre-aged at 343K for 600ks and then increased to the peak hardness with increasing aging time, which means the reversion of the Ag addition alloy.
Authors: Marat Gazizov, Viktor Telesov, Valerij V. Zakharov, Rustam Kaibyshev
Abstract: Effect of thermomechanical processing including equal-channel angular pressing (ECAP), solution treatment, water quenching and artificial aging on microstructure and mechanical properties of an Al-Cui-Mg-Ag-Sc alloy was examined. It was shown that ECAP provides extensive grain refinement. However, extensive grain growth occurs under subsequent solution treatment resulting in coarse grained structure. It was showed that ECAP following water quenching provides a minor increase in strength of the alloy. No effect of ECAP on the precipitation sequence under ageing was found. -phase precipitating under ageing condition is in dominant. As a result, the alloy exhibits high yield stress up to a temperature of 175oC. Conditions for attaining increased strength in the alloy by ECAP processing are discussed.
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