As twin-roll casting is a complex physical process, the structure and size of the metal feeding system, which supplies molten metal to the gap between two casting rolls, have a great influence on the quality of the products. In particular, the baffle is the key element for ensuring the uniformity of flow rate and temperature of molten metal at the outlet of the feeding system. The shape, size, number, and position of baffles have a significant impact on the flow characteristics of molten metal in the feeding system.

Therefore, optimizing the structure and design parameters of the feeding system is of great importance for ensuring good quality of products by adjusting the flow field of molten metal in the feeding system. In addition, the wider the strip in twin-roll casting is, the wider the feeding system gets. This increases the complexity of the flow characteristics of the molten metal, which leads to requirements for accurate structure and design parameters of the feeding system.

In order to improve the quality of strip edge in aluminum twin-roll casting, Kim Il Hyok, a student at the Faculty of Material Science and Technology, simulated the fluid flow behavior in different types of metal feeding systems (3C-type, 7C-type, and 2-split-type) by ANSYS Fluent.

Through simulations, he analyzed the effects of design parameters (shape, size, and position of baffles) of the feeding system on the distribution of fluid flow rate and temperature at the outlet of the feeding system. Based on the results, he concluded that the feeding system for the conformity of the flow rate and temperature of molten metal is of 2-split-type, and optimized its design parameters.

The optimized feeding system could ensure high quality of aluminum strips by eliminating the defects such as edge cracks.

If more information is needed, you can refer to his paper “Optimization of design parameters of metal feeding system for quality improvement of strip edge in aluminum twin-roll casting” in “The International Journal of Advanced Manufacturing Technology” (SCI).

Zirconium based alloys have been widely used in light water reactors due to their small neutron absorption cross sections, good corrosion resistance and excellent creep strength. Zircaloy-4 is a zirconium based Zr-Sn alloy, which is found in many applications in structural components such as fuel cladding tubes and pressure tubes.

Zircaloy-4 alloys are fabricated by several hot working methods such as hot rolling and hot extrusion, and numerical simulations are used to optimize and design the hot working process. So, predicting the hot flow stress evolution of Zircaloy-4 is of great importance for the numerical simulation of hot working processes.

Kim Hyok Song, a student at the Faculty of Material Science and Technology, constructed a modified Johnson-Cook model, a strain compensated Arrheniustype model, a modified Zerilli-Armstrong model and a microstructure-based model to predict the flow stress behavior of Zircaloy-4 in hot working. For this purpose, isothermal uniaxial compression tests had been conducted in the range of strain rates and deformation temperatures of 0.001-1s^-1 and 750-1 000°C. Then, he compared the prediction accuracy of the proposed constitutive models in terms of correlation coefficient and average absolute relative error.

The results showed that the microstructure-based model is the most suitable for accurately predicting the hot deformation behavior of Zircaloy-4.

You can find the details in his paper “Constitutive Models for Predicting Flow Stress Behavior of Zircaloy-4 in Thermo-Mechanical Processing” in “Physics of Metals and Metallography” (SCI).

The main metallic metals used in medicine include titanium and its alloys, Co-based alloys and austenitic stainless steels. Titanium alloys are rarely used in friction contact due to their poor abrasion resistance. Austenitic stainless steels are used for short-term implants such as screws, plates and nails because austenitic stainless steels may cause allergic reactions in many patients due to their poor corrosion resistance. Meanwhile, Co-based alloys have been widely used as femoral elements because of their good corrosion and wear resistances and biocompatibility.

Chromium and molybdenum are important alloying elements of Co-based alloys. Chromium improves resistance against oxidation and corrosion at high temperature, while molybdenum of large atomic size increases the strength through solid solution strengthening.

The understanding of the hot flow stress behavior of materials is essential for the numerical simulation of thermo-mechanical processing routes such as forging, rolling, etc. So, it is quite important to develop a constitutive material model.

Ryang Chol Song, a student at the Faculty of Material Science and Technology, developed and compared several constitutive material models for accurately predicting the flow stress during hot working of Co-28Cr-6Mo alloys.

He constructed a modified Johnson-Cook (MJC) model, a strain compensated Arrhenius-type (SCAT) model and a microstructure-based constitutive (MBC) model in a wide range of temperatures (900-1 200℃) and strain rates (0.001-10s^-1).

Then, he compared the average absolute relative error and correlation coefficient for the proposed models. The results are as follows. The correlation coefficient and AARE are 0.985 7 and 7.8% for the MJC model, 0.950 4 and 13.01% for the SCAT model, and 0.994 8 and 2.45% for the MBC model, respectively.

The results show that the proposed MBC model is best suited to predict the hot flow stress behavior of biomedical grade Co-28Cr-6Mo alloy.

For more information, please refer to his paper “Development of Several Constitutive Models to Predict Flow Stress of Biomedical Grade Co–28Cr–6Mo Alloy during Thermo-Mechanical Processing” in “Russian Journal of Non-Ferrous Metals” (SCI).