• Advances in materials Research
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• v.7 no.2
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• pp.105-118
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• 2018

Magnesium and its alloys are attracted towards all engineering applications like automotive, marine, aerospace etc. due to its inherent high strength to weight ratio. But, extensive use of Mg alloys is limited to the current scenario because of low wear and corrosion resistance behavior. However, equal channel angular press is one of the severe plastic deformation technique which has been effective method to improve the wear and corrosion resistance by achieving fine grain structure. In this study, the effect of grain refinement on wear and corrosion resistance of AZ80 Mg alloys were investigated. The wear behavior of the coarse and fine-grained Mg alloys was examined through $L_9$ orthogonal array experiments in order to comprehend the wear behavior under varies control parameters. It was shown that ECAPed alloy increased the wear and corrosion resistance of the Mg alloy through the formation of fine grain and uniform distribution of secondary ${\beta}-phase$. Also, the performance of AZ80 Mg alloy for these changeswas discussed through SEM morphology.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.11-18
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• 2004

Asymmetric rolling, in which the circumferential velocities of the upper and lower rolls are different, can give rise to intense plastic shear strains and in turn shear deformation textures through the sheet thickness. The ideal shear deformation texture of fcc metals can be approximated by the <111> // ND and $\{001\}<110>$ orientations, among which the former improves the deep drawability. The ideal shear deformation texture for bcc metals can be approximated by the Goss $\{110\}<001>\;and\;\{112\}<111>$ orientations, among which the former improves the magnetic permeability along the <100> directions and is the prime orientation in grain oriented silicon steels. The intense shear strains can result in the grain refinement and hence improve mechanical properties. Steel sheets, especially ferritic stainless steel sheets, and aluminum alloy sheets may exhibit an undesirable surface roughening known as ridging or roping, when elongated along RD and TD, respectively. The ridging or roping is caused by differently oriented colonies, which are resulted from the <100> oriented columnar structure in ingots or billets, especially for ferritic stainless steels, that is not easily destroyed by the conventional rolling. The breakdown of columnar structure and the grain refinement can be achieved by asymmetric rolling, resulting in a decrease in the ridging problem.

• Journal of Korea Foundry Society
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• v.26 no.6
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• pp.249-257
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• 2006

The effects of alloying element and the condition of heat-treatment on the strength of squeeze-cast Al-3.0 wt%Si alloy were investigated. The strength of the alloy without grain refinement was increased with increase Cu content upto 3.0 wt% and rather decreased beyond that. The tensile strength of the alloy with grain refinement increased with Cu content upto 3.0 wt% and not changed beyond that. The strength of the alloy without grain refinement increased with the Mg content. The tensile strength with grain refinement increased with the Mg content upto 0.50 wt% and then decreased beyond that. The strength of the grain refined alloy increased by individual and simultaneous additions of Cu and Mg and the maximum strength was obtained with Al-3.0 wt%Si-4.5 wt%Cu-0.50 wt%Mg alloy. The optimum heat-treatment condition for this alloy was obtained.

• Analytical Science and Technology
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• v.14 no.1
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• pp.50-58
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• 2001

The effect of cryogenic heavy rolling method on grain refinement has been studied and compared with those obtained by previous methods of cryogenic rolling and heavy rolling developed separately. Both grain structure and grain size were analyzed using electron back scattered diffraction (EBSD), which can distinguish grains each other by means of crystallographic misorientations between them. The cryogenic rolling and heavy rolling exhibit reduction in grain size of 39% and 87%, respectively, and the cryogenic heavy rolling shows reduced grain size similar to that observed in the heavy rolling. The heavy rolling was proved more effective in grain size refinement than the cryogenic rolling.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.3
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• pp.464-471
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• 2003

Among various methods to acquire high strength in plain carbon steel, the mettled of grain refinement by controlling thermo-mechanical processing parameters has gained a great attention if steel rolling industries. In the present study, three different rolling pass schedules are proposed to obtain fine grains which are based on combined results of recrystallization modelling, finite element analysis and experiment. Since meta-dynamic or dynamic recrystallization has been found to be very effective in producing fine grains, reduction ratio and interpass time in the proposed rolling pass schedules were determined in order to invoke such recrystallization as often as possible.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.188-197
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• 1999

Grain refinement of the structural steels was selected as the most effective method to meet improvement of strength and toughness without heat treatment. So, the future research and developing direction of ultra fine grain steels are more and more required to response to the production of eco - materials(environmental consciousness - materials) In this paper, the product of surface fine grain steels by CRCT and Inverse Transformation Method by warm deformation of martensite is carried out in order to improve the production process of Dowel Bar. It is possible to obtain surface ultra fine grain steel, when warm deformation of martensite formed after quenching is carried out from 730$^{\circ}C$ to 800$^{\circ}C$ in the finishing rolling step. The characters of surface with ultra fine grain steel is showing the cementite particles inside the ferrite grain and fine ferrite grain of about 1.2$\mu\textrm{m}$ in size.

• Journal of Korea Foundry Society
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• v.18 no.3
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• pp.283-288
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• 1998

Interest in rapid solidification of magnesium alloys stems from the fact that conventional ingot metallurgy alloys exhibit poor strength, ductility, and corrosion resistance. Such properties can be improved by microstructural refinement via rapid solidification processing. In this study, Mg-Zn alloys have been produced as continuous strips by melt overflow technique. In order to evaluate the influence of additional elements on the grain refinement and mechanical properties, Th and Zr were added in rapidly solidified Mg-5wt%Zn alloy. Then the microstructual observations were undertaken with the objective of evaluating the grain refinement as function of the cooling rate and the additional elements. The tremendous increase in hardness of Mg-Zn base alloys was mainly due to the refinement of the grain structure by the effect of rapid solidification and alloying elements. The formation of intermetallic phases on the grain boundaries may have a positive effect on the corroion resistance. Therefore, despite competition from many other developments, the rapid solidification processing of magnesium alloys emerges as a valuable method to develop superior and commercially acceptable magnesium alloys.

• Journal of Korea Foundry Society
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• v.23 no.2
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• pp.63-68
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• 2003

Al-Ti-C grain refiner form a relatively new alternative to the existing class of Al-Ti-B type grain refiners for achieving fine equiaxed structures in aluminum alloys during casting and solidification. The present study was carried out to investigate the influence of Al-Ti-C master alloys on the grain structure of Al-7Si alloys. The present study also investigates the relationship between grain refining efficiency and concentrations of Fe and Si in hypo-eutectic Al-Si alloys using Al-3Ti-0.13C master alloys. It is found that several parameters affect significantly the grain refining performance in silumin alloys. The present study reports the influence of various parameters such as alloy content, master alloy addition level, melt holding time and superheat on the grain refining efficiency in Al-7Si alloys.

• Korean Journal of Materials Research
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• v.19 no.11
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• pp.619-624
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• 2009

Titanium alloys have been attractive due to a high ratio of strength to weight as well as good corrosion resistance. However, strengthening causes a decrease in ductility in Ti alloys, as is usual in other alloys. For enhanced strength without ductility reduction, grain refinement and tensile properties were investigated as functions of thickness reduction of cold rolling and annealing condition in Ti-15V-3Cr-3Sn-3Al alloy with a ${\beta}$ single phase. The average grain size of the specimen, which was cold-rolled by 90% and annealed at 700$^{\circ}C$ for 5 min, was decreased to approximately 19 ${\mu}m$. The grain refinement of 63 μm to 19 ${\mu}m$ increased yield stress by 90 MPa without a significant decrease in total elongation. The Ti-15-3 alloy exhibited very low work hardening during tensile test at a crosshead speed of 2 mm/min. This result was discussed based on dynamic recovery associated with dislocation annihilation in grain boundaries.

• Transactions of Materials Processing
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• v.32 no.5
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• pp.239-246
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• 2023

To reduce the forming load due to the temperature drop, during the hot forging process, a reheating hot forging process design is required that to repeat heating and forging. However, if the critical strain required for recrystallization is not induced during forging and grain growth becomes dominant due to the reduction in dislocation density due to repeated heating, the mechanical properties may deteriorate. Therefore, in this study, Inconel 706 alloy was applied, and the grain refinement behavior was comparatively analyzed according to the number of reheating times and effective strain during reheating hot forging process. Reheating was carried out with a total compression rate of 40% up to 4 times. The Inconel 706 compression test specimens heated once showed finer grains as the effective strain increased due to the dynamic recrystallization phenomenon. However, as the number of heating increases, grain refinement was observed even in a low effective strain distribution of 0.43 due to static recrystallization during reheating. Moreover, grain growth occurs at a relatively low effective strain of 0.43 when the number of reheating is four or more. Therefore, it was effective to apply an effective strain of 0.43 or more during hot forging to Inconel 706 in order to induce crystallization through grain refinement and improve the properties of forged products. In addition, we could notice that up to three reheating times condition was appropriate to prevent grain growth and maintain fine grain size.