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.

Sushanta Kumar Panigrahi

Department of Mechanical Engineering

R. J. Immanuel

Alloys

Aluminum

Ductility

Mechanical properties

Mechanical testing

microstructure

Porosity

Silicon

Tensile strength

A356

AL-SI CAST ALLOYS

Cryo-rolling

HYPOEUTECTIC AL-SI ALLOY

Microstructural analysis

MICROSTRUCTURAL MODIFICATION

MICROSTRUCTURAL REFINEMENT

Microstructure and mechanical properties

Silicon alloys

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IIT Madras

Materials Science and Engineering A

Aluminum-copper alloy system is extensively used in structural and aerospace applications for its high strength-to-weight ratio, good mechanical and tribological properties. Improving the properties of these alloys would likely widen their application area. In the present work, an attempt has been made to simultaneously enhance the wear resistance and mechanical properties of an Al-Cu alloy, AA2014 by imparting different levels of cryorolling strains and postroll aging treatment. The wear behavior of the material is studied under dry sliding condition by pin-on-disk experiments and mechanical properties are assessed by tensile test. Formation of high fraction of dislocation density and significant refinement of microstructure during cryorolling and nucleation of fine coherent Guinier-Preston (GP) zones of Al2Cu precipitates during postcryoroll aging has led to about 100% increment in the wear resistance of the material. Tensile test results proved that the synergetic effect of cryorolling and aging treatment led to 53% increment in strength (557 MPa) without compromising the material's ductility (22.5%). A detailed investigation on the various mechanisms responsible for the enhanced wear resistance and improved mechanical performance is presented based on the microstructural evidence. © 2018 by ASME.

Journal of Tribology

Synergetic Effect of Cryorolling and Postroll Aging on Simultaneous Increase in Wear Resistance and Mechanical Properties of an Al-Cu Alloy

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

In the present work, a hybrid manufacturing route, combining stir casting with cryorolling, is proposed for production of Ultrafine grained (UFG) nano composite sheets using an Al 1050 matrix in combination with β-SiC particles (0.5 wt%, 1 wt%, 2 wt%). The method provides the scope for generating UFG microstructures with homogeneous distributions of nano particles that are difficult to achieve with existing manufacturing routes. The influence of the nano SiC reinforcement on the mechanical properties of the UFG nano composites were studied with an emphasis on the characterization of the microstructure. The results show that with an increasing content of reinforcement, the degree of grain refinement and strength of the UFG nano composite increases while the ductility reduces. The microstructural information and the obtained yield strengths of the UFG nano composites were validated with a mathematical model. For this, an existing dislocation density based model was modified to account for the effect of nano reinforcement and processing parameters. © 2018

Development of bulk ultrafine grained Al-SiC nano composite sheets by a SPD based hybrid process: Experimental and theoretical studies

Present study investigates the role of ultrasonic treatment (UT) on microstructure modification, porosity mitigation and their influence on mechanical properties of Sr modified A356 Al alloy. Addition of Sr in trace amount (500 ppm) to A356 alloy reduces the length of eutectic Si from 15.6 µm to 0.65 µm with a concomitant increase in porosity from 0.84% to 3.59%. Ultrasonic treatment of Sr modified A356 Al alloy retains the modification of eutectic Si (0.57 µm) and reduces the specific porosity volume to 0.86%. The effect of microstructure modification and porosity mitigation reflects on the mechanical properties of A356 Al alloy. While the Sr addition to A356 alloy reduces the tensile properties, UT of the Sr added alloy results in improved tensile properties. The mechanism of microstructure modification, porosity formation and UT assisted porosity mitigation are discussed in detail. Ultrasonic cavitation assisted degasification and bi-film breakage is proposed as the governing mechanism for porosity alleviation. © 2018 Elsevier B.V.

Porosity alleviation and mechanical property improvement of strontium modified A356 alloy by ultrasonic treatment

In the present work, cryorolling (CR) and room temperature rolling (RTR) followed by annealing (AN) at 200°C were carried out to investigate the effects of grain size, precipitates (Mg-Si-phases), and AlFeMnSi-phases on the fracture toughness of 6082 Al alloy. Using the values of the conditional fracture toughness, (KQ), in the critical fracture toughness (KIC) validation criteria, it was found that the sample size is inappropriate, which implies that the conditional fracture toughness obtained cannot be considered as the critical fracture toughness. Therefore, to establish the relative improvement in fracture toughness, the equivalent energy fracture toughness (Kee) and J-integral were calculated and used. The results show that the values of Kee (89.91 MPa √m) and J (89.86 kJ/m2) obtained for the sample processed via CR followed by AN (CR + AN) are the highest when compared with the other samples processed through CR, RTR, and RTR followed by AN, RTR + AN. Microstructural features such as high fraction of low Taylor factor, high fraction of kernel average misorientation, Si-rich particles, small size AlFeMnSi-phases, and mixed mode of failure (transgranular shear and micro-void coalescence) also support the high fracture toughness in the CR + AN sample. It was also observed that the effect of residual stresses on the fracture toughness of CR and RTR samples is minimal. Therefore, the correlation between microstructure and residual stresses is not considered in the present work due to very small values of the residual stresses for CR and RTR samples and the absence of residual stress from the heat-treated samples. © 2018 Wiley Publishing Ltd.

Fatigue and Fracture of Engineering Materials and Structures

Correlation of fracture toughness with microstructural features for ultrafine-grained 6082 Al alloy

Cast Al-Si alloys are used for automotive applications. Friction stir processing (FSP) is being used in recent years to improve the performance of these alloys. Secondary machining operations are highly essential on friction stir processed materials to improve the surface finish. However, machinability of friction stir processed cast alloys has rarely been reported. The influence of friction stir processing on microstructure, mechanical properties and machinability of a cast Al-Si alloy was studied in the present work. The main objective is to correlate the metallurgical and mechanical characteristics to the machinability of the friction stir processed material. The age hardening response of as received cast alloy and friction stir processed alloy on machinability and mechanical behavior was also investigated. The strength, ductility and machinability of friction stir processed alloy before and after age hardening treatment were observed to be higher than that of as received cast alloy. The significant improvement in properties of friction stir processed alloy is due to elimination of porosity, formation of fine recrystallized grain structure, homogenization of silicon particles and dissolution of iron rich intermetallics. © 2015 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.

Journal of Manufacturing Processes

Enhancing strength, ductility and machinability of a Al-Si cast alloy by friction stir processing

The effectiveness of the cryogenic (CT) rolling vis-à-vis room temperature (RT) rolling on strengthening is significantly affected by stacking fault energy (SFE) and there is an optimum SFE at which CT rolling is most effective. Studies on Al, Al alloy AA6061, Cu, Cu-4.6Al, Cu-9Al and Cu-15Al (in at.%) alloys revealed that in metals with very high and very low SFEs, the strength difference between CT and RT rolled samples is <10%. The Cu-4.6Al alloy with an intermediate SFE revealed maximum enhancement of strength (25-30%). These results are explained by changes in deformation mechanisms with SFE and temperature. High SFE metals deformed by dislocation slip and low SFE metals deformed by twinning during CT and RT rolling. Metals with intermediate SFEs deformed by twinning during CT rolling but by dislocation slip during RT rolling, and this makes the CT rolling most effective over RT rolling in enhancing the strength. © 2010 Elsevier B.V.

Role of stacking fault energy in strengthening due to cryo-deformation of FCC metals

Advanced Functional Materials

Contents: (Adv. Funct. Mater. 47/2014)

Journal of Materials Research

A critical examination of the paradox of strength and ductility in ultrafine-grained metals

Transactions of Nonferrous Metals Society of China

Strengthening contributions in ultra-high strength cryorolled Al-4%Cu-3%TiB2 in situ composite

Influence of cryorolling on microstructure and mechanical properties of a cast hypoeutectic Al-Si alloy

Journal	Data powered by TypesetMaterials Science and Engineering A
Publisher	Data powered by TypesetElsevier Ltd
ISSN	09215093
Open Access	No