In the present work, various heat treatment cycles are imposed on an A356 aluminum alloy to develop two different base microstructures, one with supersaturated aluminum matrix and the other with coarse and uniformly distributed precipitates. Both the developed materials are subjected to cryorolling and then isochronally annealed for 1 hour at various temperatures ranging from 373 K to 673 K (100 °C to 400 °C). The overall strength is maximum for the cryorolled material with supersaturated base microstructure due to the dominant dislocation strengthening and precipitation strengthening mechanisms. However, the cryorolled material with precipitated base microstructure is found to have superior microstructural stability with retained ultrafine-grained (UFG) microstructure up to the annealing temperature of 473 K (200 °C) due to effective grain boundary pinning by the precipitates. Also, the material retains about 85 pct of as-cryorolled strength with enhanced ductility even after annealing at 473 K (200 °C). A detailed investigation on the microstructural evolution of the material at various annealing temperatures along with their mechanical behavior is presented in this article. © 2017, The Minerals, Metals & Materials Society and ASM International.

Sushanta Kumar Panigrahi

Department of Mechanical Engineering

R. J. Immanuel

Aluminum

Annealing

Grain boundaries

microstructure

Strength of materials

A-356 ALUMINUM ALLOY

Annealing temperatures

DISLOCATION STRENGTHENING

HEAT TREATMENT CYCLE

Initial microstructures

MICROSTRUCTURAL STABILITY

PRECIPITATION STRENGTHENING

ULTRA FINE GRAINED MICROSTRUCTURE

Aluminum alloys

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IIT Madras

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Bulk ultrafine-grained (UFG) AA6063/4wt pct SiC composites with varying reinforcement sizes [12 µm (coarse), 1 µm (fine), and 45 nm (nano)] have been developed by a hybrid route of stir-casting and cryorolling. In the current study, the influence of annealing temperatures (423 K to 573 K) on the precipitation evolution, particle-stimulated nucleation (PSN), recrystallization, grain growth kinetics, and thermal stability of developed bulk UFG composites have been studied, and the resultant effect of microstructural evolution is correlated with mechanical properties. UFG coarse and UFG fine composites have shown evidence of recrystallized grains via PSN and retained their UFG microstructure up to 473 K and 523 K, respectively. Superior microstructural stability with retained UFG microstructure up to 573 K was observed in the UFG nanocomposite due to the effective pinning of nano-SiC particles and precipitates along grain boundaries. This ultimately resulted in the increased grain growth activation energy and strength of the UFG nanocomposite. However, the overall increase in strength is maximum in the UFG nanocomposite due to the dominant effect of dislocation strengthening, grain boundary strengthening, and precipitation strengthening mechanisms. A thorough examination of the microstructural evolution of UFG composites at different annealing temperatures along with their mechanical behavior is presented in this paper. © 2019, The Minerals, Metals & Materials Society and ASM International.

Fulltext

Thermal Stability, Grain Growth Kinetics, and Mechanical Properties of Bulk Ultrafine-Grained AA6063/SiC Composites with Varying Reinforcement Sizes

The present work investigated the synergetic effect of varying reinforcement sizes (12 μm (coarse), 1 μm (fine), 45 nm (nano)) and cryorolling on aging behavior and mechanical properties of bulk ultrafine grained (UFG) AA6063/4 wt%SiC composites produced via a hybrid route of stir casting and cryorolling. Aging of UFG composites was carried out at different temperatures in the range of 100 °C–175 °C. The results showed that decrease in SiC particle size accelerated the age hardening kinetics and the maximum age hardening effect was observed at 150 °C. The enhancement in age hardening kinetics is attributed to the presence of high dislocation density due to the (i) difference in coefficient of thermal expansion between SiC particles and matrix alloy and (ii) statistically stored dislocation during deformation. Also, the precipitation behavior in UFG composites is established and the microstructural characterization showed the accelerated precipitation kinetics in UFG nano composite. The enhanced age hardening kinetics ultimately improved the strength of the UFG composites compared to UFG base alloy. Among the UFG composites, UFG nano composite showed highest age hardening effect. The overall increase in strength in UFG nano composite is due to the dominant effect of precipitation, dislocation, and grain boundary strengthening mechanisms. © 2019

Materials Science and Engineering A

Aging behavior of ultrafine-grained AA6063/SiC composites with varying reinforcement sizes

The present research work focuses on understanding the deformation behavior of cryorolled A356 material at various strain rates ranging from 0.001 s−1 to 10 s−1 in the temperature range of 25–400 °C. Microstructure of the material at each deformation temperature was characterized to completely analyze the material's behavior. Presence of ultrafine grained microstructure with highly unstable dislocation networks were found to play a major role in strengthening the material up to the deformation temperature of 200 °C. Recrystallization and thermal softening decreases the material's strength at deformation temperatures beyond 200 °C. With respect to the rate of deformation, a prominent change in the deformation mechanism is observed at strain rates higher than 1 s−1. The failure mechanism at various strain rate and temperature ranges is studied in detail. Finally a constitutive Johnson-Cook model is developed to predict the material's flow behavior for the range of strain-rates and temperatures under study. © 2017 Elsevier B.V.

Deformation behavior of ultrafine grained A356 material processed by cryorolling and development of Johnson–Cook model

High crushing force and good energy absorption are the essential requirements for structural materials subjected to dynamic loading. In the present work, commercial A356 material is subjected to cryorolling and post-cryoroll annealing to produce sheets of different grain sizes and the influence of microstructural change on dynamic behavior of the material is studied. Dynamic tests are done in a crossbow test equipment at an average strain rate of 250 s−1. Quasi-static tests are done at an initial strain rate of 0.005 s−1 to compare the dynamic performance of the material with its static/quasi-static behavior. It is found that strength and ductility of cryorolled material at dynamic loading condition is lesser than that in quasi-static loading. Upon annealing, the material performance of the material is found to be better at high strain-rate deformation than that at quasi-static condition. A detailed analysis on the deformation behavior and fracture mechanism of the material at high strain-rate is carried out. Further, the existence of Hall-Petch relationship at high strain-rate deformation is evaluated. The material's strengthening factor is found to hold good agreement to the Hall-Petch relationship with a grain boundary strengthening coefficient of 112 MPa at dynamic loading. © 2017 Elsevier B.V.

Investigation on crashworthiness of ultrafine grained A356 sheets and validation of Hall-Petch relationship at high strain-rate deformation

The dendritic microstructure with non-uniform distribution of hard second phase particles degrades the mechanical and tribological properties of Al. Si alloys. Severe plastic deformation methods are found effective in refining microstructure and enhancing the material properties. In our present study, two different thermo-mechanical processing routes were employed on a cast hypo-eutectic Al. Si alloy to produce wrought sheets with refined microstructure. In one processing route, the material is subjected to cryorolling after solution treatment and in the other route, the material is subjected to a thermal-treatment between solution treatment and cryorolling. Cryorolling imposes severe plastic deformation onto the material resulting in refinement and redistribution of second phase particles leading to enhanced strength and ductility. Cryorolling with pre-roll thermal-treatment resulted in finer grain structures than the material without thermal-treatment. The tribological behaviour of processed materials are studied and compared with the base materials by pin-on-disk method. Maximum wear resistance is observed in thermal-treated material followed by cryorolled material with pre-roll thermal-treatment. Transformation from adhesion wear to oxidative-delamination wear is found to be the primary reason for the enhanced wear resistance in thermal-treated material. The various wear mechanisms involved are explained in detail based on the microstructural evolution and mechanical properties. © 2016 Elsevier Ltd.

Materials and Design

Transformation of cast A356 ingots to wrought sheets with enhanced mechanical and tribological properties by different thermo-mechanical processing routes

In the present work influence of annealing on precipitation phenomena, thermal stability and grain growth kinetics of a bulk ultrafine grained (UFG) Al 2014 alloy has been studied. As-received solution treated Al 2014 alloy is subjected to cryorolling (CR) to develop ultrafine grained microstructure and subsequently, annealing treatment in the range of 323 K (50 °C) to 673 K (400 °C) for the duration of 30 min is done to study its thermal stability. The recrystallization process of the cryorolled Al 2014 alloy starts at 373 K (100 °C) and completes at 523 K (250 °C). The UFG microstructure is retained in the CR Al 2014 alloy up to 623 K (350 °C). The high thermal stability of the UFG grained Al 2014 alloy is due to pinning action of precipitate particles of Cu2Al and AlCuMgSi phases which are within the range of 100 nm and lying along the grain boundaries. The activation energy required for grain growth of the CR Al 2014 alloy is found to be exceptionally high as compared to other processing routes. © 2015 Elsevier B.V. All rights reserved.

Journal of Alloys and Compounds

Precipitation phenomena, thermal stability and grain growth kinetics in an ultra-fine grained Al 2014 alloy after annealing treatment

Cast Al-Si alloys often show poor tensile strength, less ductility and poor fatigue performance due to cast microstructure and presence of porosity. An attempt has been made to improve mechanical properties of a cast hypoeutectic Al-Si alloy (A356) by cryorolling. As cast Al-Si alloy (A356) processed by cryorolling at different imposed strain levels was subjected to microstructural analysis and mechanical testing. Cryorolling resulted in break up and uniform distribution of coarse acicular eutectic particles in the aluminium matrix, elimination of casting porosity, microstructural refinement and significant accumulation of dislocation density. These microstructural changes resulted in significant improvement in the strength (248%) and ductility (37%). The influence of cryorolling on mechanism of microstructural modification, strengthening mechanism and failure mechanism are studied in detail. © 2015 Elsevier B.V.

Journal	Data powered by TypesetMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Publisher	Data powered by TypesetSpringer Boston
ISSN	10735623
Open Access	No