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정제기,옥정중,김용환,조이제,박용호 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.6
The aim of this study was to investigate the transition of wear behavior for pure aluminum and extruded aluminumalloy 2024-T4 (AA2024-T4). The wear test was carried using a ball-on-disc wear testing machine at various verticalloads and linear speeds. The transition of wear behaviors was analyzed based on the microstructure, weartracks, wear cross-section, and wear debris. The critical wear rates for each material are occurred at lower linearspeed for each vertical load. The transition of wear behavior was observed in which abrasion wears with the generationof an oxide layer, fracture of oxide layer, adhesion wear, severe adhesion wear, and the generation of seizureoccurred in sequence. In case of the pure aluminum, the change of wear debris occurred in the order of blocky,flake, and needle-like debris. Cutting chip, flake-like, and coarse flake-like debris was occurred in sequence for theextruded AA2024-T4. The transition in the wear behavior of extruded AA2024-T4 occurred slower than in purealuminum.
이은선,옥정중,김용진,박용호 대한금속·재료학회 2017 대한금속·재료학회지 Vol.55 No.2
The aim of this study is to establish an optimized hot-press sintering condition for aluminum matrix composites (AMCs) by analyzing their sintered microstructure and mechanical properties. The fabricated AMCs in this study consisted of a blend of commercial Ecka Alumix 431 powder, and Al-Si/SiCp powder manufactured by gas atomizer (Al-Si/SiCp). The Al-Si/SiCp powder was added to the Alumix 431 powder as a binder. The blended powder was hot-pressed and sintered and its properties were analyzed based on three variables: the blending ratio of each powder, sintering time and sintering temperature. The MgZn2 phases in the Alumix 431 powder were finely and homogeneously distributed when the sintering temperature was increased. The liquid phase of the Al-Si alloy facilitated densification of the Alumix 431 particles and promoted a reduction in pores in the sintered body. Dispersion of the MgZn2 phases, degree of porosity and densification of the fabricated AMCs affected the ultimate tensile strength (UTS) of the sintered body at room temperature (RT). The highest UTS of the fabricated AMCs was 242MPa at RT. The optimum sintering conditions were: a mixing ratio of Al-Si/SiCp to Alumix 431 powders of 5 to 95 wt%, a sintering time of 30 min and a sintering temperature of 610 ℃. Wear behavior of the specimens prepared with the optimized sintering conditions included stick-slip, abrasive, adhesive and delamination phenomena for each test condition, under correlated vertical load and linear speed.
Fe-17Mn-5Si-5Cr 형상기억합금의 형상복원거동 및 기계적 특성에 미치는 Ni, Ti 및 C의 영향
김도형,김용환,옥정중,이정훈,박찬희,이욱진,박용호 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.10
Fe-Mn-Si based shape memory alloy is a new functional material that can be used to apply prestress to civil and structural components such as concrete structures. In this study, the effects of alloying elements Ni, C and Ti on the mechanical and shape memory properties of the alloy were investigated in detail using a base alloy composition of Fe-17Mn-5Si-5Cr (wt%). Enhanced shape recovery ratio and decreasing strength were observed in the alloy when 4 wt% Ni was added. With the further addition of 0.05 wt% C, the alloy showed even higher shape recovery behavior, although the mechanical strength was lowered by the C addition. Increasing the carbon content up to 0.1 wt% led to higher mechanical strength while the shape recovery ratio was decreased slightly. It was shown that the addition of 1 wt% Ti can significantly enhance the shape recovery behavior of the alloy. The recovery behavior of the alloy with the co-addition of 0.3 wt% C and 1 wt% Ti was similar to the alloy without Ti but containing 0.1 wt% C, even though the C content was significantly higher. The alloy with the co-addition of 0.3 wt% C and 1 wt% Ti has great potential as functional components in prestressed civil engineering structures, since the yield strength of the alloy is as high as 400 MPa in the solution heat treated condition and can be further improved by aging heat treatments, which precipitate TiC particles.