Papers by Author: Dong-Seok Chung

Abstract: After extrusion, cold rolling and T-6 treatment, microstructure, texture development, and deep drawability of Al-5.09%Zn-1.83%Mg-0.32%Cu-0.25%Mn-alloy with 0.1% Sc are studied. After T-6 treatment, recrystallized equiaxed grains with an average grain size of 1~2㎛ are obtained. During extrusion the very strong <111>-fiber + medium sharp <100>-fiber + weak <210>-fiber texture is developed, which influences the formation of rolling texture. The texture, after 80% cold rolling, can be described by the strong {112}<111>(Cu) + {123}<634>(S) component in the cross section of the extruded rod, the strong b-fiber + weak {110}<001>(Goss) components in the longitudinal section, and the strong {110}<112>(Bs) + weak {001}<100>(Cube) components in the transverse section. The types of rolling texture are not changed after the T-6 treatment, but the maximum density of ODF is higher. The calculated mean r-values, rm, and the planar anisotropy, Dr, are relatively high, which are dependent on the texture.

Abstract: Ni/Ni-aluminide//Ti/Ti-aluminide laminate composite, considered as a functionally gradient material, was manufactured by thin foil hot press technique. Thick intermetallic layers of NiAl and TiAl3 were formed by a self-propagating high-temperature synthesis (SHS) reaction, and thin continuous layers of Ni3Al and TiAl were formed by a solid-state diffusion. Fracture resistance with loading along the crack arrester direction is higher than crack divider direction due to the interruption of crack growth in metal layers. The Ni3Al and NiAl intermetallic layer showed cleavage and intergranular fracture behavior, respectively, while the fracture mode of TiAl3 layer was found to be a intragranular cleavage. The debonding between metal and intermetallic layer and the pores were observed in the Ni/Ni-aluminide layers, resulting in the lower fracture resistance.

Abstract: The effect of beryllium (Be) on the precipitation behaviors and mechanical properties of Al–Cu–Li–Mg–Zr–(Ag) alloys was investigated. The results show that adding 0.02%Be to Al–Cu–Li–Mg–Zr–(Ag) alloys, the elongation of the alloy increased without significant decrease in strength and the aging response was accelerated. In a Al–Cu–Li–Mg–Zr–(Ag) alloy, G.P. zone was formed at early aging time (2 h) and T1 and q′ phases were formed at peak-aging and over-aging times, while in Al–Cu–Li–Mg–Zr–(Ag)–Be alloys T1 and q′ phases were formed at early aging time (2 h) and the density of q′ phase was very low and fine T1 phases were homogeneously distributed at peak-aging and over-aging times.