Byung-Wook Ahn

Fabrication of SiCp/AA5083 composite via friction stir welding

Abstract Microstructure and mechanical properties of SiC p /AA5083 composite fabricated by friction stir welding (FSW) were investigated. The influence of the number of FSW passes on the distribution of SiC particles and mechanical properties in the joint was studied. After one pass, the SiC particles were entangled in the upper side of the stir zone (SZ). However, the particle distribution became more uniform after two passes due to the repeated stirring of the joint. As the SiC particles facilitate the grain refinement in the SZ by the pinning effect, the particle including region has much smaller grain size than the SZ without SiC particles. The SiC p /AA5083 composite region exhibits a Vickers hardness of HV90, which is much higher than the value of HV80 in the SZ produced by FSW without SiC particles.

Microstructure and mechanical property of A356 based composite by friction stir processing

Abstract Friction stir processing (FSP) was used to incorporate SiC particles into the matrix of A356 Al alloy to form composite material. Constant tool rotation speed of 1800 r/min and travel speed of 127 mm/min were used in this study. The base metal (BM) shows the hypoeutectic Al-Si dendrite structure. The microstructure of the stir zone (SZ) is very different from that of the BM. The eutectic Si and SiC particles are dispersed homogeneously in primary Al solid solution. The thermo-mechanically affected zone (TMAZ), where the original microstructure is greatly deformed, is characterized by dispersed eutectic Si and SiC particles aligned along the rotational direction of the tool. The hardness of the SZ shows higher value than that of the BM because some defects are remarkably reduced and the eutectic Si and SiC particles are dispersed over the SZ.

Hybrid Friction Stir Welding of High-carbon Steel

A high-carbon steel joint, SK5 (0.84 wt% C), was successfully welded by friction stir welding (FSW), both without and with a gas torch, in order to control the cooling rate during welding. After welding, the weld zone comprised gray and black regions, corresponding to microstructural variation: a martensite structure and a duplex structure of ferrite and cementite, respectively The volume fraction of the martensite structure and the Vickers hardness in the welds were decreased with the using of the gas torch, which was related with the lower cooling rate.

Interfacial Reaction and Joint Strength of the Sn-58Bi Solder Paste with ENIG Surface Finished Substrate

Abstract Sn-Bi eutectic alloy has been widely used as one of the key solder materials for step soldering at low temperature. The Sn-58Bi solder paste containing chloride flux was adopted to compare with that using the chloride-free flux. The paste was applied on the electroless nickel-immersion gold (ENIG) surface finish by stencil printing, and the reflow process was then performed at 170℃ for 10 min. After reflow, the solder joints were aged at 125℃ for 100, 200, 300, 500 and 1000 h in an oven. The interfacial microstructures were obtained by using scanning electron microscopy (SEM), and the composition of intermetallic compounds (IMCs) was analyzed using energy dispersive spectrometer (EDS). Two different IMC layers, consisting of Ni 3 Sn 4 and relatively very thin Sn-Bi-Ni-Au were formed at the solder/surface finish interface, and their thickness increased with increasing aging time. The wettability of solder joints was investigated by wetting balance test. The mechanical property of each aging solder joint was evaluated by the ball shear test in accordance with JEDEC standard (JESD22-B117A). The results show that the highest shear force was measured when the aging time was 100 h, and the fracture mode changed from ductile fracture to brittle fracture with increasing aging time. On the other hand, the chloride flux in the solder paste did not affect the shear force and fracture mode of the solder joints.Key Words : Sn-58Bi solder paste, Wettability, Intermetallic compound (IMC), Aging, Shear test

Electroless Ni alloy plating as a diffusion barrier for through silicon vias in three-dimensional packaging

Ni- and Co-based amorphous films are alternative diffusion barrier materials for Cu interconnection in three-dimensional (3D) packaging applications. In this paper, electroless Ni–P and Ni–W–P films deposited in through-silicon vias (TSVs) were prepared as a diffusion barrier and seed layer of Cu filling by using Sn–Pd activation pretreatment. The thermal stability of the electroless Ni alloy films subjected to rapid thermal annealing (RTA) in H2 atmosphere was investigated. The barrier properties of the electroless Ni alloy films were evaluated over a range of temperatures using auger electron spectroscopy (AES) and energy dispersive X-ray spectroscopy (EDS) line-scan. The microstructures, crystal structures and electrical resistivity were also examined. It was found that Ni alloy films are amorphous as deposited, that the films retain amorphous or amorphous-like structures after undergoing annealing at 400 °C for 1 h, and that they are feasible for the diffusion barrier layer for 3D Cu interconnect technology.

Friction Stir Welding of Duplex Stainless Steel

합금 등의 고융점 재료에 대해서도 최근 활발히 연구되고 있고 접합 특성도 우수하여 그 적용이 검토되고 있다. 그러나 Al 및 Mg 합금과 같은 비철금속재료의 접합과는 달리 고융점 재료의 접합에는 고가의 툴이 요구되고 있으며 접합 시에는 툴이 마모되는 문제점이 발생한다. 이러한 문제점을 극복하고 고융점 재료에 대한 마찰교반접합의 적용이 확대되기 위해서는 툴 재질 및 접합공정 개발이 매우 중요하며 이에 대한 연구 또한 활발히 진행되고 있다. 최근 스테인리스강의 개발은 Ni 원료 가격의 급격한 상승으로 인하여 Ni 함량이 높은 기존의 오스테나이트 스테인리스강에서 상대적으로 Ni의 함유량이 적어 가격 경쟁력이 있는 2상 스테인리스강으로 대체하려는 움직임이 증가하고 있다. 2상 스테인리스강은 오스테나이트 상과 페라이트 상이 1:1로 혼합된 미세조직을 갖는 스테인리스강으로서 강도가 높고, 내공식성이 우수하며 특히 오스테나이트계 스테인리스강에서 가장 문제가 되는 응력부식균열 저항성이 매우 우수한 것으로 알려져 있다

Recent Studies on Friction Stir Welding of High Carbon Steels

. 따라서 고탄소강 및 초고탄소강의 마찰교반접합에 관한 연구에서도 이와 같은 조직의 변화를 고려한 접합특성 개선이 집중 검토되고 있다. 이러한 연구들이 훌륭한 성과를 거두어 고탄소강의 용접이 쉽게 이루어 질 수 있다면 각종 산업분야에서 고탄소강의 적용이 획기적으로 확대될 수 있으므로 최근의 관련 연구는 항상 중요한 관심의 대상이 되고 있다. 따라서 본 보고에서는 고탄소강의 마찰교반접합에 대하여 지금까지 발표된 연구결과를 중심으로 접합 조건에 따른 접합부의 미세조직, 기계적 특성 그리고 템퍼링 처리에 따른 조직의 변화 등을 종합하여 소개하고자 한다.

Microstructures and mechanical properties of MgOp/SPHC metal matrix composites joint by friction stir welding:

The SPHC/MgO composites were fabricated by friction stir welding (FSW) and then the mechanical property of the composites was investigated. MgO particles were flocculated on the advancing side in the stir zone (SZ) formed by one-pass processing. On the other hand, MgO particles were more homogenously distributed in the SZ formed by two-pass processing. Compared to the SZ without MgO particles, the hardness profile of the SZ with MgO particles was increased to 20–30 Hv due to refined grain by pinning effect. Grain growth in the SZ without MgO particles was observed at elevated temperature. On the other hand, the fine grain produced with MgO particles was maintained at elevated temperature (∼900℃) due to pinning effect by MgO particles.

Friction Stir Welding of Ferritice Stainless Steel

Ferritic stainless steels are widely used in the construction industry and in exhaust manifolds due to their low cost and relatively superior stress corrosion cracking resistance and pitting corrosion resistance compared to austenite stainless steels. Ferritic stainless steels are currently welded by various welding process including gas tungsten arc welding (GTAW), electron resistance welding (ERW) and laser beam welding. However, when these stainless steels are welded by fusion welding, some problems occur in the fusion zone (FZ) and heat affected zone (HAZ). First, the ductility of the weld is reduced due to the grain growth in the FZ and HAZ. Second, as its HAZ is frequently sensitized during welding, corrosion resistance deteriorates in this region due to the Cr depletion zone. To prevent these problems, it is recommended that ferritic stainless steels be welded with a low heat input. In this study, recent researches in the view of friction stir welded ferritic stainless steels are briefly reviewed.

Researches in Corrosion Resistance of Friction Stir Welded Aluminum alloys

Aluminum alloys have been considered for substantial use in these industries. This ensues from their attractive strength to weight ratio, superb formability, apposite weldability and acceptable corrosion resistance. Depending on the specific application, corrosion behavior is a significant factor of a welded joint. In this study, recent researches in the view of corrosion resistance of friction stir welded aluminum alloys are briefly reviewed.