Donghyun Bae

A new Mg-RE-Zn-Al alloy reinforced with the second phase of Mg12(RE) has been developed to enhance mechanical properties at the elevated temperatures. When the alloy solidifies with a relatively high cooling rate under the pressure applied, an extremely fine α-Mg phase with a completely closed network of the second phase of Mg12(RE) is developed. The reinforcing network restricts grain boundary sliding during deformation, resulting in a high yield strength of 150 MPa at 150 °C. Furthermore, the

This study has been investigated the deformation behavior of a hot-extruded Mg-Zn-RE (RE: rare earth elements) alloy containing Mg12(RE) particles at the elevated temperatures. The particles are intrinsically produced by breaking the eutectic structure of the alloy during the hot-extrusion process. The grain size of the extruded Mg-Zn-RE alloy developed via dynamic recrystallization is around 10 μm. Under the heat treatment at 200℃ up to 48 hr, no change has been observed on the microstructure a

A statically recrystallized Mg-3Al-1Zn alloy was fabricated by low temperature roll heating (140 °C) processes and subsequent annealing at 250 °C for 5 min. The fabricated sheet, with a grain size of 4.1 m, shows an improved planar anisotropy and higher elongations to failure at room temperature and 200 °C, compared with those of the sheet fabricated by conventional hot rolling processes, due to the weak basal texture along with the refined microstructure.

The Mg-Zn-RE alloy cladded with the thin Al1050 sheet was fabricated by means of a roll bonding process at 280℃. Microstructures and mechanical properties of the clad sheets were investigated. After heat treatment at 230℃ for 30 min, an Mg-rich diffusion layer with about 2 μm in thickness was developed at the Mg and Al interface. Tensile tests were carried out in a temperature range up to 300℃. The clad sheet exhibits superior elongation to failure not only at room temperature but also at elevat

This study investigated the effects of aging profiles on the precipitate formation and the corresponding strengthening and deformation behaviors of Al-Mg-Zn alloys. The alloys subjected to natural aging (NA) demonstrated significantly enhanced ductility at equivalent stress levels compared to those subjected to artificial aging (AA). In AA-treated alloys, η' and η-phases with incoherent interfaces were formed, while GP zones and solute clusters were dominantly exhibited in the NA-treated alloy w

The Mg-Zn-RE alloy cladded with the thin Al1050 sheet was fabricated by means of a roll bonding process at 280°C. Microstructures and mechanical properties of the clad sheets were investigated. After heat treatment at 230°C for 30 min, an Mg-rich diffusion layer with about 2 μm in thickness was developed at the Mg and Al interface. Tensile tests were carried out in a temperature range up to 300°C. The clad sheet exhibits superior elongation to failure not only at room temperature but also at ele

The crack propagation behavior of Al containing Mg-Si clusters is investigated using molecular dynamics (MD) simulations to demonstrate the relationship between the natural aging time in Al-Si-Mg alloys and ductility. Experimental results show that the elongation at failure decreases with natural aging. There are few studies on the relationship between natural aging and ductility because of the difficult observation of Mg-Si clusters. To solve the difficulty, cracked Al containing Mg-Si clusters

The influence of cluster composition and the addition of vacancies on the decomposition behavior of clusters during artificial aging in Al-Si-Mg alloys were analyzed according to the kinetic Montel Carlo model. Clusters with a balanced composition (Mg/(Mg + Si) = 0.5) were the most difficult to decompose. In addition, the cluster decomposition was slower when more vacancies were added to the cluster. Among Si, Mg, and vacancies, vacancies most significantly affect decomposition. The clusters wit

Electrically conductive epoxy composites were developed by adding cilia-like powders produced by dispersing multi-walled carbon nanotubes (MWNTs) on copper particles via mechanical milling. During the milling process, the MWNTs were gradually dispersed and partially embedded in the copper particles, producing cilialike powders that enhanced the electrical conductivity of the epoxy composites. With further milling, however,excessive embedding of the MWNTs in the copper particles resulted in decre

Interfacial bonding between aluminum and nanoscale ceramic reinforcements is often weak, limiting the mechanical performance of aluminum matrix nanocomposites (AMNCs) relative to theoretical predictions. This study investigates how incorporated oxygen alters the interfacial structure and bonding chemistry in multi-walled carbon nanotube (MWCNT)-reinforced AMNCs and examines the resulting mechanical response through in-situ tensile testing and nanoindentation. An Al–O/MWCNT composite was fabricat

Supersaturated Cu-Sn alloy sheets were successfully fabricated by hot-rolling mechanically alloyed (MAed)nanocrystalline powders within a range of up to 22 wt.% of Sn, and their antibacterial and ionization properties were investigated. While the pure Cu and hot-rolled Cu-Sn sheets using MAed powders show excellent antibacterial properties, the corrosion potential of the hot-rolled Cu-Sn using MAed powders is much less than that of the as-cast Cu-Sn and decreases as the Sn content increases, imp

공학교육의 패러다임은 학습내용, 학습결과 중심의 패러다임에서 학습자, 학습과정 중심의 패러다임으로 변화하고 있고, 이러한 패러다임의 전환에서 실험 교과목은 학습자 중심의 교육을 실현하기에 가장 적합한 교과목이다. 본 연구에서는 학부 2, 3, 4학년 전 과정에 걸친 실험 교과목의 교육과정 개발의 맥락 속에서 2학년 실험 교과목을 전공기초 지식 습득 및 기초실험 능력 배양을 목표로 학습자 중심 교과목으로 교육과정을 개발하고 적용하고자 하였다. 교육과정 개발을 위하여 국내외 우수대학 재료공학과의 실험 교과목을 비교 분석하였고 학생 설문 조사를 실시하여 학생들의 요구를 반영하였다. 개편된 기초실험을 위한 교육과정은 학생들의 요구를 반영한 교육내용으로 학생들의 참여를 독려함으로써 학생들로부터 비교적 긍정적인 피드백을 받고 있는 것으로 나타났다.