본 연구는 구리 아연 금속합금의 산화 환원 반응과 합성 알루미늄 실리케이트의 흡착 반응을 이용한 폐수 중 중금속 처리에 관한 연구이다. 극세사 형태로 제조된 구리 아연 금속합금이 수용액 중에 서 산화 환원반응에 의해 아연보다 이온화 경향이 작은 중금속은 환원 처리되고, 이온화 된 아연 및 미 반응 중금속은 흡착 처리하여 제거하는 연구이다. 극세사 형태로 제조된 금속합금 물질은 표면적이 커서 1회 처리만으로도 반응 평형에 도달하게 하여 효율이 높은 것으로 나타났다. 크롬(Cr+3)은 redox 반응 1 회 처리만으로도 100.0 % 제거 되었으며, 수은은 98.0 %, 주석 92.0 %, 구리는 91.4 % 정도 제거되었 다. 카드뮴, 니켈, 납도 각각 40.0 %, 50.0 %, 58.0 %가 제거 되었다. 크롬(Cr+3)은 아연과 이온화 경향 차이가 거의 없지만 제거 효율이 높은 것으로 나타났는데 이는 3가 크롬은 이온 상태로 존재하면 redox 반응에서 발생한 OH- 이온과 결합하여 수산화물 침전을 형성하는 것으로 판단된다. Redox 반응 후 증 가한 아연 및 미반응 중금속 농도를 알루미늄실리케이트를 1회 통과하여 거의 100.0 % 제거할 수 있었 다. 이는 합성 알루미늄 실리케이트의 비표면적이 크고 금속 이온의 흡착능력이 우수한 것으로 나타났으 며, 반응 후 알루미늄 이온은 증가하지 않는 것으로 보아 이온 교환이 아닌 흡착으로 아연 및 중금속 이 온들을 제거할 수 있는 것으로 나타났다.

In this study, the recently developed Al 2013 alloy was T8-tempered and, to improve the strength and corrosionresistance, slight amounts of Zr of 0.2 wt% and 0.5 wt%, respectively, were added and the mechanical properties were analyzed. For microstructure and precipitate analysis, OM observation, XRD analysis, and TEM analysis were performed, and for the mechanical property analysis, hardness and tensile strength tests were done. Also, in order to determine the corrosion rate according to the Zr content, a potentiodynamic polarization test was performed and the properties were compared and analyzed. The size of the precipitate varied with the content of Zr and was finest at Zr content of 0.2 wt%; it grew larger at 0.5 wt%, at which point the hardness value accordingly showed the same trend. On the other hand, as calculated from the aspect of chemical bonding among atoms, it was confirmed that the tensile strength and the corrosion-resistance increased with the same trend.

Tensile tests and creep tests were carried out at high temperatures on an Al-Al4C3 alloy prepared by mechanical alloying technique. The material contains about 2.0 % carbon and 0.9 % oxygen in mass percent, and the volume fractions of Al4C3 and Al2O3 particles are estimated at 7.4 and 1.4 %, respectively, from the chemical composition. Minimum creep rate decreased steeply near two critical stresses, σcl (the lower critical stress) and σcu (the upper critical stress), with decreasing applied stress at temperatures below 723 K. Instantaneous plastic strain was observed in creep tests above a critical stress, σci, at each test temperature. σcu and σci were fairly close to the 0.2% proof stress obtained by tensile tests at each test temperature. It is thought that σcl and σcu correspond to the microscopic yield stress and the macroscopic yield stress, respectively. The lower critical stress corresponds to the local yield stress needed for dislocations to move in the soft region within subgrains. The creep strain in the low stress range below 723 K arises mainly from the local deformation of the soft region. The upper critical stress is equivalent to the macroscopic yield stress necessary for dislocations within subgrains or in subboundaries; this stress can extensively move beyond subboundaries under a stress above the critical point to yield a macroscopic deformation. At higher temperatures above 773 K, the influence of the diffusional creep increases and the stress exponent of the creep rate decreases.

The effect of heat treatment on the microstructure and mechanical properties of cast Ti-6%Al-4%V alloy was investigated. Heat treatment of cast Ti-6Al-4V alloy was conducted by solution treatment at 950 oC for 30 min; this was followed by water quenching and then aging at 550 oC for 1 to 1440 min. The highest hardness of the heat-treated specimens was obtained by solution treatment and subsequent aging for 5 min due to precipitates of fine α that formed from retained β phase. The tensile strength of this alloy increased without dramatic decrease of the ductility due to microstructural refinement resulting from the decomposition of α' martensite into fine α and β phases, and also due to the fine α phase formed from the retained β phase by aging treatment for 5 min. In addition, this strengthening might be caused by the transformation induced plasticity (TRIP) effect, which is a strain-induced martensite transformation from the retained β phase during deformation, and which occurs even after aging treatment at 550 oC for 5 min.

Titanium has many special characteristics such as specific high strength, low elastic modulus, excellent corrosion and oxidation resistance, etc. Beta titanium alloys, because of their good formability and strength, are used for jet engines, and as turbine blades in the automobile and aerospace industries. Low cost beta titanium alloys were developed to take economic advantage of the use of low-cost beta stabilizers such as Mo, Fe, and Cr. Generally, adding a trace of boron leads to grain refinement in casted titanium alloys due to the pinning effect of the TiB phases. This study analyzed and evaluated the microstructural and mechanical properties after plastic deformation and heat treatment in boron-modified Ti-2Al-9.2Mo-2Fe alloy. The results indicate that a trace of boron addition made grains finer; this refinement effect was found to be maintained after subsequent processes such as hot forging and solution treatment. This can effectively reduce the number of required manufacturing process steps and lead to savings in the overall cost as well as low-cost beta elements.

In this work, ceramic coatings were prepared on Al7075 aluminum alloy using microarc oxidation (MAO) process in a silicate-fluoride based electrolyte solution. The effect of OH− concentration, by adding NaOH to the solution on the microstructural and mechanical properties of the coating was investigated. Surface morphology and cross sectional view of the coating was analyzed using SEM while XRD was used to examine the phase compositions of the coatings. From XRD α-Al2O3 phase was found to be increased by adding NaOH to the electrolyte. Thereby, the hardness and the wear properties of the MAO coatings were found to be superior to those of the coatings prepared without NaOH addition or with amount maximum than 2 g/l NaOH. Moreover, the morphology of the coatings was transformed form nodule-based cluster to crater based structure with the addition of NaOH to the MAO electrolyte solution.

Microstructural analysis of a (α+β) Ti alloy was investigated to consider phase transformation in each step of thethermo-mechanical process using by SEM and TEM EDS. The TAF (Ti-6Al-4Fe) alloy was thermo-mechanically treated withsolid solution at 880oC, rolling at 880oC and annealing at 800oC. In the STQ state, the TAF microstructure was composedof a normal hcp α and metastable β phase. In a rolled state, it was composed of fine B2 precipitates in an α phase, whichhad high Fe segregation and a coherent relationship with the β matrix. Finally, in the annealing state, the fine B2 precipitateshad disappeared in the α phase and had gone to the boundary of the α and β phase. On the other hand, in a lower rollingtemperature of 704oC, the B2 precipitates were more coarse in both the α and the boundary of α and β phase. We concludedthat microstructural change affects the mechanical properties of formability including rolling defects and cracks.

NiO catalysts/Al2O3/FeCrAl alloy foam for hydrogen production was prepared using atomic layer deposition (ALD)and subsequent dip-coating methods. FeCrAl alloy foam and Al2O3 inter-layer were used as catalyst supports. To improve thedispersion and stability of NiO catalysts, an Al2O3 inter-layer was introduced and their thickness was systematically controlledto 0, 20, 50 and 80nm using an ALD technique. The structural, chemical bonding and morphological properties (includingdispersion) of the NiO catalysts/Al2O3/FeCrAl alloy foam were characterized by X-ray diffraction, X-ray photoelectronspectroscopy, field-emission scanning electron microscopy and scanning electron microscopy-energy dispersive spectroscopy. Inparticular, to evaluate the stability of the NiO catalysts grown on Al2O3/FeCrAl alloy foam, chronoamperometry tests wereperformed and then the ingredient amounts of electrolytes were analyzed via inductively coupled plasma spectrometer. We foundthat the introduction of Al2O3 inter-layer improved the dispersion and stability of the NiO catalysts on the supports. Thus, whenan Al2O3 inter-layer with a 80nm thickness was grown between the FeCrAl alloy foam and the NiO catalysts, it indicatedimproved dispersion and stability of the NiO catalysts compared to the other samples. The performance improvement can beexplained by optimum thickness of Al2O3 inter-layer resulting from the role of a passivation layer.

The effect of Al content on the processing of reaction-bonded Al2O3 (RBAO) ceramics using 40v/o ~ 80v/o Al- Zn-Mg alloy powder was studied in order to improve traditional RBAO ceramic processes that use ~ 40v/o pure Al powder. The influence of high Al content in starting Al2O3-Al alloy powder mixtures on its particulate characteristics, reaction-bonding, microstructure, physical and mechanical properties was revealed. Starting Al2O3-Al alloy powder mixtures with 40v/o ~ 80v/o Al alloy powder were milled, reaction-bonded, post-sintered, and characterized. With an increasing Al alloy content, the milling efficiency of Al alloy powder was lowered, resulting in a larger particle size after milling. However, in spite of the larger particle size of Al alloy powder, the oxidation, i.e., reaction-bonding, of the Al alloy was successfully completed via solid and liquid state oxidation, in which the activation energy of the oxidation was nearly the same regardless of Al alloy content. After reaction-bonding and post-sintering at 1600 oC, RBAO ceramics from 80v/o Al alloy content showed a relative density of ~97% and a flexural strength of 251 MPa compared to ~ 96% and 353 MPa for RBAO ceramics from 40v/o Al alloy content, respectively. The lower flexural strength at 80v/o Al alloy content was due to the weak spinel phase that formed from Zn, Mg alloying elements in Al.

Al-Si-SiC composite powders with intra-granular SiC particles were prepared by a gas atomization process. The composite powders were mixed with Al-Zn-Mg alloy powders as a function of weight percent. Those mixture powders were compacted with the pressure of 700 MPa and then sintered at the temperature of 565-585˚C. T6 heat treatment was conducted to increase their mechanical properties by solid-solution precipitates. Each relative density according to the optimized sintering temperature of those powders were determined as 96% at 580˚C for Al-Zn-Mg powders (composition A), 97.9% at 575˚C for Al-Zn-Mg powders with 5 wt.% of Al-Si-SiC powders (composition B), and 98.2% at 570˚C for Al-Zn-Mg powders with 10 wt.% of Al-Si-SiC powders (composition C), respectively. Each hardness, tensile strength, and wear resistance test of those sintered samples was conducted. As the content of Al-Si-SiC powders increased, both hardness and tensile strength were decreased. However, wear resistance was increased by the increase of Al-Si-SiC powders. From these results, it was confirmed that Al-Si-SiC/Al-Zn-Mg composite could be highly densified by the sintering process, and thus the composite could have high wear resistance and tensile strength when the content of Al-Si-SiC composite powders were optimized.

Microstructural and mechanical characteristics of Al-6Si-2Cu alloy for lightweight automotive parts were investigated. The test specimens were prepared by gravity casting process. Solution heat treatments were applied to as-cast alloys to improve mechanical properties. The microstructure of the gravity casting specimen presents a typical dendrite structure, having a secondary dendrite arm spacing (SDAS) of 37μm. In addition to the Al matrix, a large amount of coarsened eutectic Si, Al2Cu intermetallic phase, and Fe-rich phases were identified. After solution heat treatment, single-step solution heat treatments were found to considerably improve the spheroidization of the eutectic Si phase. Two-step solution treatments gave rise to a much improved spheroidization. The mechanical properties of the two-step solution heat treated alloy have been shown to lead to higher values of properties such as tensile strength and microhardness. Consequentially, the microstructural and mechanical characteristics of Al alloy have been successfully characterized and are available for use with other basic data for the development of lightweight automotive parts.

The effects of processing parameters on the flow behavior and microstructures were investigated in hotcompression of powder metallurgy (P/M) Ti-6Al-4V alloy. The alloy was fabricated by a blended elemental (B/E)approach and it exhibited lamellar α+β microstructure. The hot compression tests were performed in the range of tem-perature 800-1000℃ with 50℃ intervals, strain rate 10−4-10 s−1, and strain up to 0.5. At 800-950℃, continuous flowsoftening after a peak stress was observed with strain rates lower than 0.1 s−1. At strain rates higher than 1 s−1, rapiddrop in flow stress with strain hardening or broad oscillations was recorded. The processing map of P/M Ti-6Al-4V wasdesigned based on the compression test and revealed the peak efficiency at 850℃ and 0.001 s−1. As the processing tem-perature increased, the volume fraction of β phase was increased. In addition, below 950℃, the globularization of phaseat the slower strain rate and kinking microstructures were found. Based on these data, the preferred working conditionof the alloy may be in the range of 850-950℃ and strain rate of 0.001-0.01 s−1.

Fabrication of reaction-bonded Al2O3 (RBAO) ceramics using Al-Zn-Mg alloy powder was studied in order to improve traditional RBAO ceramic processing using Al powder. The influence on reaction-bonding and microstructure, as well as on physical and mechanical properties, of the particulate characteristics of the Al2O3-Al alloy powder mixtures after milling, was revealed. Variation of the particulate characteristics of this Al2O3-Al alloy powder mixture with milling time was reported previously. To start, the Al2O3-Al alloy powder mixture was milled, reaction-bonded, post-sintered, and characterized. During reaction-bonding of the Al2O3-Al alloy powder mixture compacts, oxidation of the Al alloy took place in two stages, that is, there was solid- and liquid-state oxidation of the Al alloy. The solid-state oxidation exhibited strong dependence on the density of surface defects on the Al-alloy particles formed during milling. Higher milling efficiency resulted in less participation of the Al alloy in reaction-bonding. This was because of its consumption by chemical reactions during milling, and subsequent powder handling, and could be rather harmful in the case of over-milling. In contrast to very little dependence of oxidation of the Al alloy on its particle size after milling, the relative density, microstructure, and flexural strength were strongly dependent on particle size after milling (i.e., on milling efficiency). The relative density and 4-point flexural strength of the RBAO ceramics in this study were ~98% and ~365 MPa, respectively, after post-sintering at 1,600˚C.

In this paper, the effects of precipitates and Mn-solute atoms on the recrystallization behavior of an Al-Mn alloy was studied using micro-Vickers hardness, electrical conductivity measurements and optical microscopy. Various thermo-mechanical processes were designed to investigate the different morphologies, and the solute concentration, of Mn in the matrix. The results indicate that the recrystallization temperature, TR and time, tR, are influenced by the amount of M-solute atoms in the matrix, and that the recrystallization microstructure is influenced by the amount of precipitates. Recrystallization in the Slow-Cooling specimen was rapid due to its low concentration of Mn-solute atoms, and the crystal-grain size was the smallest due to finely distributed precipitates. However, in the case of the No-Holding specimen, elongated grains were observed at the low annealing temperature and the largest recrystallized grains were observed at the high annealing temperatures (compared with Slow-Cooling and Base specimens) due to the high Mn-solute atoms in the matrix.

The milling and particulate characteristics of Al alloy-Al2O3 powder mixtures for a reaction-bonded Al2O3 (RBAO) process were studied. A commercially available prealloyed Al powder with Zn, Mg, Cu and Cr alloying elements (7475 series) was mixed with a calcined sinter-active Al2O3 powder and then milled in centrifugal milling equipment for ~48 hrs. The Al alloy-Al2O3 powder mixtures after milling were characterized and evaluated in various ways to reveal their particulate characteristics during milling. The milling efficiency of the Al alloy increased with a longer milling time. Comminution of the Al alloy particles started with its elongation, showing a high aspect ratio. With a longer milling time, the elongated Al alloy particle changed in terms of its shape and size, becoming equiaxially fine particles. Regardless of the milling efficiency of the Al alloy particles, all of the Al alloy particles repeatedly experienced strong plastic deformation during milling, giving rise to higher density of surface defects, such as microcracks, and leading to higher residual microstress within the Al alloy particles. The chemical reactions, oxidation behavior and hydration behavior of the Al alloy particles and the hydrolysis characteristics of their reaction with the environment were also observed during the milling process and during the subsequent powder handling steps.

A5J32-T4 and A5052-H32 dissimilar aluminum alloy plates with thickness of 1.6 and 1.5 mm were welded by friction stir lap welding (FSLW). The FSLW were studied using different probe length tool and various welding conditions which is rotation speed of 1000, 1500 rpm and welding speed of 100 to 600 mm/min and material arrangement, respectively. The effects of plunge depth of tool and welding conditions on tensile properties and weld nugget formation. The results showed that three type nugget shapes such as hooking, void, sound have been observed with revolutionary pitch. This plunge depth and material arrangement were found to effect on the void and hooking for- mation, which in turn significantly influenced the mechanical properties. The maximum joint efficiency of the FSLWed plates was about 90% compared to base metal, A5052-H32 when the A5052-H32 was positioned upper plate and plunge depth was positioned at near interface between upper and lower plates.

Al-based alloys have recently attracted considerable interest as structural materials and light weight materials due to their excellent physical and mechanical properties. For the investigation of the potential of Al-based alloys, a surface porous Al88Cu6Si6 eutectic alloy has been fabricated through a chemical leaching process. The formation and microstructure of the surface porous Al88Cu6Si6 eutectic alloy have been investigated using X-ray diffraction and scanning electron microscopy. The Al88Cu6Si6 eutectic alloy is composed of an α-Al dendrite phase and a single eutectic phase of Al2Cu and α-Al. We intended to remove only the α-Al phase and then the Al2Cu phase would form a porous structure on the surface with open pores. Both acidic and alkaline aqueous chemical solutions were used with various concentrations to modify the influence on the microstructure and the overall chemical reaction was carried out for 24 hr. A homogeneous open porous structure on the surface was revealed via selective chemical leaching with a H2SO4 solution. Only the α-Al phase was successfully leached while the morphology of the Al2Cu phase was maintained. The pore size was in a range of 1~5μm and the dealloying depth was nearly 3μm. However, under an alkaline NaOH, aqueous solution, an inhomogeneous porous structure on the surface was formed with a 5 wt% NaOH solution and the morphology of the Al2Cu phase was not preserved. In addition, the sample that was leached by using a 7 wt% NaOH solution crumbled. Al extracted from the Al2Cu phase as α-Al phase was dealloyed, and increasing concentration of NaOH strongly influenced the morphology of the Al2Cu phase and sample statement.

일반적으로 중성용액 하에서 알루미늄 합금은 부동태피막(Al2O3나 Al2O3·3H2O)을 형성한다. 그러나, 해수 환경에서 염소이온이 표면에 생성된 부동태 피막을 파괴하여 부식이 발생하게 된다. 본 연구에서는 해수환경 하에서 부식 문제점을 해결하기 위해 Al-4.5%Mg-0.6%Mn 알루미늄 합금에 대하여 정전위 방식 기술을 적용하였다. 분극실험결과, 개로전위보다 귀한 전위에서는 활성 용해 반응이 나타났으며 개로전위 보다 비한 전위에서는 용존산소 환원에 의한 농도 분극과 활성화 분극이 관찰되었다. 정전위 실험결과, 농도 분극에서 활성화 분극으로 전환되는 전위부터 적용 시간이 증가할수록 전착물이 많이 생성되었으며, 부분적으로 전착물과 모재의 계면사이에서 틈부식이 관찰되었다. 전체적으로 정전위 양극분극실험시, 활성용해반응이 발생하여 정전위 방식 기술을 적용하기 어려운 반면, 정전위 음극분극 실험시 방식 전위인 농도분극 범위내에서 적용 시간을 고려하여 최적 방식 조건을 -1.1 V~-0.75 V로 규명하였다.