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© 2019, The Korean Institute of Metals and Materials. Abstract: This study discusses the superior effect of thixoforming process on enhancing the tensile properties of aluminium matrix composite produced using flake metallurgy route. The flake metallurgy process was utilised to manufacture aluminium matrix composites followed by thixoforming process. Microstructural investigations carried out using transmission electron microscope have shown the synergic effect of thixoforming process on rendering uniform distribution of SiC nanoparticles associated with lower porosity content. X-ray diffraction characterisations have revealed the promising effect of uniform dispersion of SiC nanoparticles on restricting the grain growth of aluminium matrix within nanoscale regime (90 nm) even at high semi-solid thixoforming temperatures (575 °C). The achieved results of tensile tests have shown a profound effect of flake metallurgy of aluminium powder through dual speed ball milling. These results are higher than those achieved by low speed and high speed even with higher SiC content. This was attributed to the uniform confinement of SiC nanoparticles within the samples produced using flake-assisted forming process compared to the ones manufactured using ball milling-assisted processes. Graphic abstract: [Figure not available: see fulltext.].

© 2018 Elsevier B.V. This study reveals an unprecedented capacity of flake graphene sheets in manipulating semi-solid deformation of aluminium matrix nanocomposites by restricting the grain growth of the nanograins during the reheating process to significantly enhance (173%) the yield strength of the fabricated composites. The graphene sheets with onion shape have also shown the unique capability in alleviating the agglomeration of SiC nanoparticles, attributed to the manipulated Hamaker constant of these particles as a result of wrapping graphene sheets. A devised mathematical approach has authenticated, for the first time, the effect of wrapping graphene sheets on subtle adjusting the Hamaker constant of SiC nanoparticles to stimulate engulfment of these nanoparticles within solidifying matrix rather than agglomeration at grain boundaries. This, therefore, has resulted in diminishing the porosity and stimulating multi-scaled micro/nano grains, thereby significantly enhancing the tensile properties of the fabricated composites.

© 2016 Elsevier Ltd. All rights reserved. This study reveals a promising feature of graphene encapsulating process to significantly enhance the mutually inclusive tensile strength and ductility of aluminium based composites using the semi-solid powder forming process. It was corroborated based on van der Waals-Casimir interaction free energy that graphene sheets have an unprecedented capacity to manipulate the Hamaker constant of SiC nanoparticles, prompting formation of nano/micro-sized grains. Authenticating by the strengthening model, fractographic observations have also demonstrated the unique functionality of graphene sheets in strengthening via grain refining, thermally enhanced dislocations, shear-lag, geometrically necessary dislocations, crack bridging and fibre pull out mechanisms.

© 2016 Trans Tech Publications, Switzerland. In hot rolling, metal oxides formed on steel surface can generally be classified as primary, secondary and tertiary oxide scales, corresponding to the reheating stages, the roughing stages and the finishing passes of continuous mills, respectively. The tertiary oxide scale grows into the final products on the hot-rolled steel strip during the finishing rolling and the subsequent cooling down to ambient temperature. We provide here a systematic overview of the oxidation mechanism, microstructure and microtexture development of the tertiary oxide scale. Mechanism of oxidation and Fe3O4 precipitation in tertiary oxide has been given as the fundamental theory. Three main sections has been divided in this review. The first section includes experimental investigations on microstructure evolution from the formation of oxide scale during hot rolling, then through continuous cooling, to Fe3O4 precipitation behaviour in storage cooling of hot-coiled strip. By using electron backscatter diffraction (EBSD) to characterise both the steel substrate and the oxide scale concurrently, the second section has further dealed with the texture-based analysis of oxide scale: phase identification, orientation analysis and coincident site lattice (CSL) boundaries. The third section has provided the general type of crystallographic texture and its evolutions in deformed Fe3O4 and steel substrate. Finally, the upcoming challenges have been addressed in this intriguing and promising research field.

© 2015 Elsevier B.V. In this study, β-SiC nanoparticles were well dispersed in a matrix of aluminium making use of encapsulation capacity of graphene sheets, semi-solid stirring of the aluminium melt, ultrasonic treatment, and pressure application during solidification. A new solidification model taking into account the alteration of the solidification mechanism from particle pushing to particle engulfment, making use of at least 40% enhancement in higher thermal conductivity and diminished repelling forces of SiC nanoparticles tuned by encapsulating graphene sheets was suggested. This nanostructure manipulation can make about 350% and 258% enhancement in yield strength and tensile ductility, respectively, compared to that of unreinforced aluminum alloy. The results achieved based on the devised analytical model have shown the significant effect of thermal activated dislocation in strengthening due to considerable mismatch between thermal expansion coefficient of graphene sheets and aluminium matrix. Fractographic observations disclosed a dimple fracture surface for the semi-solid-processed aluminium matrix composite reinforced by the nanoparticles that were encapsulated by graphene sheets using ball-milling process compared with the cleavage fracture surface of those fortified without the application of graphene.

To understand the high temperature flow behaviour of a novel pearlitic steel (PS) and low carbon steel (LCS) bimetal, hot compression tests in a wide range of temperature and strain rate were conducted on a Gleeble 3500 thermo mechanical simulator, and the constitutive model was developed based on the experimental data. The measured true stress-strain curves exhibited three types of variation patterns, which are (i) a plateau type, (ii) single peak type and (iii) multi peaks type. These patterns well displayed the effects of the deformation temperature, strain rate and plastic strain on the flow behaviour of the bimetal. By incorporating the Zener-Hollomon parameter and material parameter functions of α(ε), n(ε), Q(ε) and A(ε) into Arrhenius-type constitutive equation, the flow stress values predicted by the proposed model show a good agreement with experimental results by the evidence of reproducing true stress-strain curves accurately, high value of correlation coefficient (R=0.9873) and low value of average absolute relative error (AARE=4.81%). The proposed constitutive equation can be used to realise numerical simulation and determine processing parameters during hot-working of the PS/LCS bimetal. © 2013 Elsevier B.V.

Controlling cold strip profile is a difficult and significant problem has been found in industry during thin strip rolling. At present choosing the new type of strip rolling mill is the one of main methods to control the strip shape quality in cold rolling. The influences of rolling process parameters such as the work roll cross angle and work roll shifting on the strip shape and profile of thin strip are recognised throughout this study. The results show that the roll crossing and shifting is efficient way to control the strip shape. The increase of the work roll crossing angle would lead to improve the strip profile significantly by decreasing the exit strip crown and edge drop. The strip profile would be enhanced if the axial roll shifting was increased. Moreover, the total rolling force was analysed in detail by changing the roll cross angle and axial shifting roll. © (2014) Trans Tech Publications, Switzerland.

© (2014) Trans Tech Publications, Switzerland. A novel microforming process - Micro Cross Wedge Rolling (MCWR) has been developed. It is a very promising technology in the field of microforming due to its advantages such as high product rate and minimised material consumption. How to control geometrical accuracy of the produced micro parts is one of the major challenges in the development of microforming technology. Geometrical accuracy was still concentrated in term of springback. When the wedge tools loads are removed after forming step, a portion of the deformation recovers, which causes a change in the shape of micro parts. In other word, springback happens, which should be determined and controlled especially in microforming technology. A series of MCWR experiments of pure copper and aluminium have been carried out using the machine designed by authors in this study. Cylindrical workpieces were deformed into stepped shafts with cross-sectional area reductions of 35, 52.73 and 75%. Corresponding finite element simulation has also been conducted in consideration of the size effect on the material flow. The springback was proposed to account for the geometrical error of micro products. The effect of grained heterogeneity on the height of surface asperity after rolling was assessed quantitatively.

The friction is a key factor that influences the surface quality in metal forming. To figure out the relationship between the friction and the surface roughening, a finite element model is employed in the commercial finite element software ABAQUS to simulate the surface roughness of top side of Al plate during uniaxial planar compression. With the change of friction conditions, the surface roughening varies. The average surface roughness (Ra) shows a relationship with the friction coefficient. During the surface roughening process, the grain slip takes place in the "soft orientation", and the "hard orientations" become the barrier of the slip. © Trans Tech Publications.

The demand of thin gauge strip with good quality such as the strip shape and surface finish is significantly increasing. In this study, finite element model of the strip shape during cold rolling of thin strip in asymmetrical rolling was developed, and the finite element simulation of the thin strip shape has been carried out in LS-DYNA. The effects of reduction and speed ratio on the strip shape and profile and the strip edge drop have been obtained. The developed finite element model has been verified with the experimental data. The obtained results are applicable to the control of the rolled thin strip shape in rolling practice. © (2010) Trans Tech Publications.

In this paper, the cold rolling experiments of ultra thin steel strip were carried out on an experimental rolling mill. The cold rolling of ultra thin strip with roll edge kiss was analysed theoretically, and the rolling force, intermediate force between the work roll and backup roll, the roll edge kiss force, the strip shape after rolling are obtained for this special rolling, and they are compared for various reduction and friction coefficients. Simulation results show that the reduction has a significant influence on the shape of rolled strip, and the calculated rolling forces and strip profile are consistent with the measured values. The effect of friction in the roll bite on cold rolling of ultra thin strip with roll edge kiss is also discussed. Surface characteristic was measured and it is shown that the steel surface roughness value reduces with an increase of reduction. © 2008 Elsevier B.V. All rights reserved.