Papers by Author: Geun Tae Bae

Abstract: An attempt has been made to clad Mg alloy with Al by twin-roll casting. This was done by inserting an Al sheet between the roll and the Mg alloy melt during twin-roll casting. Microstructural investigation across the transverse section of the as-cast Al-clad Mg alloy sheet reveals a very good interfacial bonding between Al and the base Mg alloy. Annealing of the Al-clad Mg alloy sheet results in the formation of layers of various intermetallic phases along the Mg/Al interface. Subsequent rolling of the as-annealed sheet significantly improves the formability of the reaction zone, as evidenced by the cracking of the base Mg alloy before the cracking of the reaction zone.

Abstract: Room temperature formability of twin-roll cast Mg alloys has been investigated and correlated with their work hardening behavior. Tensile properties of these alloys were measured and their work hardening behaviour was analysed by using constitutive equations. Room temperature formability of the alloys was evaluated by the limiting dome height (LDH) value, obtained by the Erichsen cupping test. It shows that there is a linear relationship between LDH value and the inverse of yield ratio, which is a function of work hardening exponents. An increase in grain size increases work hardening exponent and concurrently increases LDH.

Abstract: Development of wrought Mg alloys, particularly in sheet form, is essential to support the growing interest for lightweight components in the automotive industry. However, development of Mg alloy sheets has been quite slow due to the complexity of sheet production originated from limited deformability of Mg. In this respect, twin-roll strip casting, a one-step processing of flat rolled products, can be an alternative for the production of Mg alloy sheets. In this study, AZ31 and experimental ZM series alloys are twin-roll strip cast into 2 mm thick sheets. The microstructure of the as-cast AZ31 alloy sheet consists of columnar zones near the roll side and equiaxed zones in the mid-thickness region. On the other hand, as-cast ZM series alloy sheets show equiaxed dendritic structure through the thickness of sheet. These alloys were subjected to various thermo-mechanical treatments and their tensile properties were evaluated. Twin-roll strip cast AZ31 alloy in H24 condition has equivalent yield and tensile strengths with similar ductility compared to commercial ingot cast AZ31-H24 alloy, indicating that twin-roll strip casting is a viable process for the fabrication of Mg alloy sheets. The experimental ZM series alloys have a large volume fraction of fine dispersoid particles in the microstructure, resulting from the beneficial effect of twin-roll strip casting on microstructural refinement. It has been shown that the experimental ZM series alloys have superior tensile properties compared to commercial ingot cast AZ31-H24 alloy, suggesting the possibility of the development of new wrought Mg alloy sheets by twin-roll strip casting.

Abstract: AZ31 and experimental ZMA611 alloys were strip cast into 2 mm thick strips. The as-cast AZ31 alloy strip consists of columnar dendrites. On the other hand, as-cast ZMA611 alloy strip shows equiaxed dendritic structure through the thickness of strip. Strip cast AZ31 alloy in H24 condition has equivalent yield and tensile strengths with similar ductility compared to commercial ingot cast AZ31-H24 alloy, indicating that strip casting is a viable process for the fabrication of Mg alloy strips. The ZMA611 alloy has a large volume fraction of fine dispersoid particles in the microstructure, resulting from the beneficial effect of strip casting on microstructural refinement. It has been shown that the ZMA611 alloy has superior tensile properties compared to commercial ingot cast AZ31-H24 alloy, suggesting the possibility of the development of new wrought Mg alloy sheets by strip casting.