The effects of annealing on the microstructure and mechanical properties of Al–Zn–Mg–Cu–Si alloys fabricated by high-energy ball milling (HEBM) and spark plasma sintering (SPS) were investigated. The HEBM-free sintered alloy primarily contained Mg2Si, Q-AlCuMgSi, and Si phases. Meanwhile, the HEBM-sintered alloy contains Mg-free Si and θ-Al2Cu phases due to the formation of MgO, which causes Mg depletion in the Al matrix. Annealing without and with HEBM at 500oC causes partial dissolution and coarsening of the Q-AlCuMgSi and Mg2Si phases in the alloy and dissolution of the θ-Al2Cu phase in the alloy, respectively. In both alloys, a thermally stable α-AlFeSi phase was formed after long-term heat treatment. The grain size of the sintered alloys with and without HEBM increased from 0.5 to 1.0 μm and from 2.9 to 6.3 μm, respectively. The hardness of the sintered alloy increases after annealing for 1 h but decreases significantly after 24 h of annealing. Extending the annealing time to 168 h improved the hardness of the alloy without HEBM but had little effect on the alloy with HEBM. The relationship between the microstructural factors and the hardness of the sintered and annealed alloys is discussed.

Aluminum alloys are extensively employed in several industries, such as automobile, aerospace, and architecture, owing to their high specific strength and electrical and thermal conductivities. However, to meet the rising industrial demands, aluminum alloys must be designed with both excellent mechanical and thermal properties. Computer-aided alloy design is emerging as a technique for developing novel alloys to overcome these trade-off properties. Thus, the development of a new experimental method for designing alloys with high-throughput confirmation is gaining focus. A new approach that rapidly manufactures aluminum alloys with different compositions is required in the alloy design process. This study proposes a combined approach to rapidly investigate the relationship between the microstructure and properties of aluminum alloys using a direct energy deposition system with a dual-nozzle metal 3D printing process. Two types of aluminum alloy powders (Al-4.99Si-1.05Cu-0.47Mg and Al-7Mg) are employed for the 3D printing-based combined method. Nine types of Al-Si-Cu-Mg alloys are manufactured using the combined method, and the relationship between their microstructures and properties is examined.

Cr-Si based alloys are not only excellent in corrosion resistance at high temperatures, but also have good wear resistance due to the formation of Cr3Si phase, therefore they are promising as metallic coating materials. Aluminum is often added to Cr-Si alloys to improve the oxidation resistance through which stable alumina surface film is formed. On the other hand, due to the addition of aluminum, various Al-containing phases may be formed and may negatively affect the heat resistance of the Cr-Si-Al alloys, so detailed investigation is required. In this study, two Cr-Si-Al alloys (high-Si & high-Al) were prepared in the form of cast ingots through a vacuum arc melting process and the microstructural changes after high temperature heating process were investigated. In the case of the cast high-Si alloy, a considerable amount of Cr3Si phase was formed, and its hardness was significantly higher than that of the cast high-Al alloy. Also, Al-rich phases (with the high Al/ Cr ratio) were not found much compared to the high-Al alloy. Meanwhile, it was observed that the amount of the Al-rich phases reduced by the annealing heat treatment for both alloys. In the case of the high temperature heating at 1,400 oC, no significant microstructural change was observed in the high Si alloy, but a little more coarse and segregated AlCr phases were found in the high Al alloy compared to the cast state.

In this study, the effects of powder size and composition on the reflectance of Al-Si based alloys are presented. First, the reflectance of Al-Si bulk and powder are analyzed to confirm the effect of powder size. Results show that the bulk has a higher reflectance than that of powder because the bulk has lower surface defects. In addition, the larger the particle size, the higher is the reflectance because the interparticle space decreases. Second, the effect of composition on the reflectance by the changing composition of Al-Si-Mg is confirmed. Consequently, the reflectance of the alloy decreases with the addition of Si and Mg because dendrite Si and Mg2Si are formed, and these have lower reflectance than pure Al. Finally, the reflectance of the alloy is due to the scattering of free electrons, which is closely related to electrical conductivity. Measurements of the electrical conductivity based on the composition of the Al-Si-Mg alloy confirm the same tendency as the reflectance.

In order to develop a new commercial Al-12%Si casting alloy with improved physical properties, we investigated the effect of adding Sr and TiB to the alloy. Al-12%Si alloys were prepared by die casting at 660 oC. The eutectic temperature of the Sr-modified Al-12%Si alloy decreased to 9 oC and the mushy zone region increased. The shape of the Si phase changed from coarse acicula to fine fiber with the addition of Sr. The addition of TiB in the Al-12%Si alloy reduced the size of the primary α-Al and eutectic Si phases. When Sr and TiB were added together, it worked more effectively in refinement and modification. The density of twins in the Si phase-doped Sr increased and the width of the twins was refined to 5 nm. These results are related to the impurity induced twinning(IIT) growth.

The cold rolling workability and mechanical properties of two new alloys, designed and cast Al-5.5Mg-2.9Si and Al-7Mg-0.9Zn alloys, were investigated in detail. The two alloy sheets of 4 mm thickness, 30 mm width and 100 mm length were reduced to a thickness of 1 mm by multi-pass rolling at ambient temperature. The rolling workability was better for the Al-7Mg-0.9Zn alloy than for the Al-5.5Mg-2.9Si alloy; in case of the former alloy, edge cracks began to occur at 50% rolling reduction, and their number and length increased with rolling reduction; however, in the latter alloy, the sheets did not have any cracks even at higher rolling reduction. The mechanical properties of tensile strength and elongation were also better in the Al-7Mg-0.9Zn alloy than in Al-5.5Mg-2.9Si alloy. Work hardening ability after cold rolling was also higher in the Al-7Mg- 0.9Zn alloy than in the Al-5.5Mg-2.9Si alloy. At the same time, the texture development was very similar for both alloys; typical rolling texture developed in both alloys. These differences in the two alloys can primarily be explained by the existence of precipitates of Mg2Si. It is concluded that the Al-7Mg-0.9Zn alloy is better than the Al-5.5Mg-2.9Si alloy in terms of mechanical properties.

Two types of nanoclusters, termed Cluster (1) and Cluster (2) here, both play an important role in the age-hardening behavior in Al-Mg-Si alloys. Small amounts of additions of Cu and Ag affect the formation of nanoclusters. Two exothermic peaks were clearly detected in differential scanning calorimetry(DSC) curves by means of peak separation by the Gaussian method in the base, Cu-added, Ag-added and Cu-Ag-added Al-Mg-Si alloys. The formation of nanoclusters in the initial stage of natural aging was suppressed in the Ag-added and Cu-Ag-added alloys, while the formation of nanoclusters was enhanced at an aging time longer than 259.2 ks(3 days) of natural aging with the addition Cu and Ag. The formation of nanoclusters while aging at 100˚C was accelerated in the Cu-added, Ag-added and Cu-Ag-added alloys due to the attractive interaction between the Cu and Ag atoms and the Mg atoms. The influence of additions of Cu and Ag on the clustering behavior during low-temperature aging was well characterized based on the interaction energies among solute atoms and on vacancies derived from the first-principle calculation of the full-potential Korrinaga-Kohn-Rostoker(FPKKR)-Green function method. The effects of low Cu and Ag additions on the formation of nanoclusters were also discussed based on the age-hardening phenomena.

High heat-resistant Al-Fe-V-Si and Al-Fe-V-Si-X rapidly solidified powder metallurgy (RS P/M) alloys have been developed under well-controlled high purity argon gas atmosphere. The (at. %) RS P/M alloy exhibited high elevated-temperature strength exceeding 300 MPa and good ductility with elongation of 6 % at 573 K. Reduction of partical pressure in P/M processing atmosphere led to improvement in mechanical properties of the powder-consolidated alloys under elevated-temperature service conditions. Ti addition to the Al-Fe-V-Si conduced to enhancement of the strength at room temperature. The tensile yeild strength and ultimate strenght were 545 MPa and 722 MPa, respectively.

Wear behaviors of gas atomized and extruded Al-Si alloys were investigated using the dry sliding wear apparatus. The wear tests were conducted on Al-Si alloy discs against cast iron pins and vice versa at constant load of 10N with different sliding speed of 0.1, 0.3, 0.5m/s. In the case of Al-Si alloy discs slid against the cast iron pins, the wear rate slightly increased with increasing the sliding speed due to the abrasive wear occurred between Al-Si alloy discs and cast iron pins. Conversely, in the case of cast iron discs against Al-Si alloy pins, the wear rate decreased with increasing the sliding speed up to 0.3m/s. However, the wear rate increased with increasing the sliding speed from 0.3m/s to 0.5m/s. It could be due to adhesive wear behavior and abrasive wear behavior_between cast iron discs and Al-Si alloy pins.

The effect of extrusion temperature on the microstructure and mechanical properties was studied in gas atomized TEX>Al81Si19 alloy powders and their extruded bars using SEM, tensile testing and wear testing. The Si particle size of He-gas atomized powder was about 200-800 nm. Each microstructure of the extruded bars with extrusion temperature (400, 450 and 50) showed a homogeneous distribution of primary Si and eutectic Si particles embedded in the Al matrix and the particle size varied from 0.1 to 5.5 . With increasing extrusion temperature from 40 to 50, the ultimate tensile strength (UTS) decreased from 282 to 236 ㎫ at 300 K and the specific wear increased at all sliding speeds due to the coarse microstructure. The fracture behavior of failure in tension testing and wear testing was also studied. The UTS of extrudate at 40 higher than that of 50 because more fine Si particles in Al matrix of extrudate at 40 prevented crack to propagate.

The effect of Pb addition on microstructure and wear resistance was studied in rapidly solidified Al-20Si-5Fe-xPb(x=2, 4, 6 wt.%) alloys. The R/S Al-20Si-5Fe-xPb (x=2, 4, 6 wt.%) alloys showed a fine and homogeneous microstructure and an improved wear property compared with Al-20Si-5Fe alloy, while no significant change in UTS (Ultimate Tensile Strength) was shown. Contribution of the dispersoids on the wear property was discussed by showing the plastic deformation layers formed during wear track.

The plastic deformation behaviors for powder extrusion of rapidly soildified Al-Si-Fe alloys at high temperature were investigated. During extrusion of Al-Si-Fe alloys, primary Si and intermetallic compound in matrix are broken finely. Additionally, during extrusion metastable phase() intermetallic compound disappears and the equilibrium phase() is formed. In gereral, it was diffcult to establish optimum process variables for extrusion condition through experimentation, because this was costly and time-consuming. In this paper, in order to overcome these problems, we compared the experimental results to the finite element analysis for extrusion behaviors of rapidly solidified Al-Si-Fe alloys. This ingormation is expected to assist in improving rapidly solidified Al-Si alloys extrusion operations.

The densification behaviors of rapidly solidified Al-Si alloys under high temperature processing were investigated. In general, it was difficult to establish optimum process variables for forging condition through experimentation, because this was costly and time consuming. In this paper, to overcome these problems, we compared the experimental result to the finite element analysis for forging processes of rapidly solidified Al-Si alloys. The results of these simulations helped understand the distribution of relative density during various forging processes. This information is expected to assist in improving rapidly solidified Al-Si alloys forging operations.

Investigation on the extrusion of rapidly solidified Al-Si alloys was performed in order to develop an inexpensive production process of high strength parts. It is necessary to establish optimum process variables for the extruding condition through the experiments, because it is high cost and time consuming process. In this paper, the experimental results was compared to the finite element analysis for the extrusion of rapidly solidified Al-Si alloys. The results of this simulation helped to understand the distribution of relative density and effective stress for rapidly solidified Al-Si alloys during the extrusion process. This information is expected to assist in improving the extrusion operations of rapidly solidified Al-Si alloys.

과공정 Al-18wt%Si합금의 초정 Si입자의 미세화에 미치는 첨가원소의 영향에 관하여 조사하였다. 초정 Si입자의 크기는 P량이 증가함에 따라 미세해졌으며 적정 P량은 40ppm이었다. 최적주입온도는 AlCuP, CuP 경우 각각 750˚C, 800˚C이었으며 미세화 처리 후 10분 이상 경과되어도 초정 Si입자의 크기는 변화가 없었다. 또한 WDS분석 결과 초정 Si내에 AIP가 핵생성 site로 존재함을 알 수 있었다.

Alloying behavior of nanocrystalline Al-Ti-(Si) composite powders via mechanical alloying (MA) has been investigated, and the effect of Si on the microstructural changes during MA was discussed. The microstructures of both MA powders and extruded compacts were examined. In Al-Ti system, the solid solutionized nanocrystalline powders could be obtained by MA. On the contrary, fine Si particles were embedded as an elemental state in the matrix of Al-Ti-Si system because of the brittleness and the negligible solid solubility of Si in Al. After hot extrusion, phase was finely precipitated in Al-10fSTi alloy, and Si particles were dissolved to form phase in Al-10%Ti-2%Si alloy.

현재까지 잘 알려진 압출이론식이 생산현장에 응용될 수 있는가를 조사하기 위하여, Al-Si합금을 대상소재로 하여 각 압출이론식에 나타난 유도응력 Kf, 변형저항 Kw , Dead Metal Zone(DMZ)의 경각(α)등을 측정하였으며, 이들 값을 이용하여 최대압출력을 계산하였다. 550ton의 압출기를 이용하여 측정한 최대 압출력과의 비교분석을 행하였으며, 그 결과 이론식에 의해 최대압출력을 계산하기 위해 측정된 유동응력 및 변형저항 값은 신뢰할 수 있을 것으로 사료되었는데, 이것은 0.5이하에서 결정된 변형효율 η f로서 판단 할 수 있었다. 최대 압출력은 Si함량이 증가할 수록 증가하게 되나, 압출온도가 증가할 수록 감소하고 있음을 알 수 있었다. Siebel식으로부터 계산된 최대압출력은 본 실험을 통하여 얻어진 최대압출력에 비교적 근접하고 있으나. Geleji식으로부터 계산된 최대압출력은 DMZ의경각 α가 50˚일 경우 , 본 실험에 의해 얻어진 실제의 최대압출력에 급접하고 있었다. Geleji의 식은 DMZ의 경각에 매우 민감하고, 대상재료마다. DMZ를 일일이 측정해야 하는 번거로움 때문에 생산현장에서는 Siebel의 식을 이용하는 것이 보다 편리할 것으로 사료된다.