• Journal of Advanced Marine Engineering and Technology
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• 제35권1호
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• pp.75-81
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• 2011

이종합금인 알루미늄 합금 6061-T6와 알루미늄 합금 5083-O의 용접을 위해 마찰교반 용접기술을 사용하였다. 마찰교반 용접된 이종 접합부에 대하여 기계적 특성, 경도 및 조직변화를 관찰하였다. 용접재의 기계적특성은 후진 측에 위치한 알루미늄 합금의 교반영역에 형성되는 미세조직이 주요한 변수로 작용하였다. 이종 알루미늄 합금이 교차한 양파 모양 형상의 얇은 층을 이루었다. 미세조직관찰에서 공구회전방향과 무관하게 이종합금 접합부에 기공이 관찰되지 않았으나 6061-T6 쪽 열영향부 영역에서 결정립 조대화기 뚜렷하였다. 본 논문의 연구결과, 결함이 없는 최상의 용접조건은 Al 6061-T6를 공구 진행방향에 전진 측에, Al 5083-O를 후진 측에 위치하고, 이송속도 124 mm/min, 1250 rpm의 공구의 회전수, 5 mm의 프루브 직경, 4.5 mm의 프루브 길이, 20 mm의 공구어깨, $2^{\circ}$의 공구 경사각 이다. 이때 용접재의 최대인장강도는 231 MPa이였고, 항복강도는 121 MPa을 나타내었다.

• 소성∙가공
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• 제30권5호
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• pp.219-225
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• 2021

When extruding Al6061 alloys, deformation energy is deposited inside the extruded alloy depending on the deformation and the temperature of extrusion. This creates a Peripheral Coarse Grain (PCG) on the surface, where relatively more deformation energy. of the extruded alloy has been accumulated. Furthermore, since the deformation of materials continues while the materials recrystallize, it is important to examine the effect of deformation energy on dynamic recrystallization in the process of extruding Al alloys along with their microstructure. Prior studies explain the theory behind PCG growth though quantitative analysis on PCG growth of Al alloys during extrusion processes has not yet been addressed. This study aims to measure the generated PCG thickness which determines the correlation between extrusion outlet temperature and its effect on mechanical properties. Surface structure observations were performed using Optical Microscope (OM) and mechanical properties were evaluated through tensile strength and hardness measurement. Throughout this study, we endevoured to find the optimum condition of extrusion exit temperature of Al6061 and confirmed improved d reliability. This study describes the effect of the complex process variables such as exit temperature on the thickness of PCG layer for the Al6061 alloy using the 200 tons extrusion press. We therefore, discovered that the PCG layer thickness was 117 ㎛ at temperatures between 460 ℃ to 520 ℃.

• Corrosion Science and Technology
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• 제19권5호
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• pp.250-258
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• 2020

Recently, 5000 series and 6000 series Al alloys have been used as hull materials for small and medium-sized ships because of their excellent weldability, corrosion resistance, and durability in marine environments. Al ships can navigate at high speed due to their light weight. However, cavitation-erosion problems cause reducing durability of Al ship at high speed. In this investigation, 5052-O, 5083-H321, and 6061-T6 Al alloy materials were used to evaluate the damage characteristics with amplitude (cavitation strength). As a result of the electrochemical experiments, the corrosion current density and corrosion potential of 6061-T6 in seawater were 8.52 × 10-7 A/㎠ and -0.771 V, respectively, presenting the best corrosion resistance. The cavitation-erosion experiment showed that 5052-O had the lowest hardness value and cavitation-erosion resistance. 5052-O also had a very short incubation period. As the experiment progressed for 5052-O, pitting formed and grew in a short time, and was observed as severe cavitation-erosion damage that eliminated in large quantities. Among the three specimens, 5083-H321 presented the highest hardness value and the damage rate was the smallest after the initiation of pitting.

• 대한기계학회논문집A
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• 제33권7호
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• pp.693-699
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• 2009

This paper shows mechanical properties and behaviors of macro- and micro-structures on friction stir welded specimen with 6061-T6 aluminum alloy plate. It apparently results in defect-free weld zone jointed at welding conditions like the traverse speed of 267mm/min, tool rotation speed of 2500rpm, pin inserted depth of 4.5mm and tilting angle of $2^{\circ}$ with tool dimensions such as tool pin diameter of 5mm, shoulder diameter of 15mm and pin length of 4.5mm. The tensile stress ${\sigma}_T=228MPa$ and the yield point ${\sigma}Y=141MPa$ are obtained at the condition of traverse speed of 267mm/min and tool rotation speed of 2500rpm. With the constant rotation speed, the higher traverse speed become, the higher tensile stress and yielding point become. Vickers hardness for welding zone profile were also presented.

• 한국전기전자재료학회논문지
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• 제34권1호
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• pp.68-72
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• 2021

Aluminum is a lightweight metal and has excellent properties with regard to conductivity, workability, and strength. It has been used in various industries owing to its economic benefits. To improve upon the mechanical properties and processability by adding various alloying elements to aluminum, improving the corrosion resistance and heat resistance by electrochemically forming a porous anodic film having a thickness and hardness on the surface of the aluminum alloy is crucial. In this study, the aluminum 6061 alloy was controlled by an anodization process in a 0.3M oxalic acid electrolyte at room temperature to investigate the oxide film parameters such as porosity and thickness depending on the modulating applied voltage and time. The anodizing experiment was performed by increasing the time from 1 h to 9 h at 2-h intervals at applied voltages of 50 V and 60 V.

• 한국표면공학회지
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• 제54권1호
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• pp.30-36
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• 2021

In this study, double-layered anodizing films were formed on Al 5052 and Al 6061 alloys consecutively first in sulfuric acid and then in oxalic acid, and hardness, withstand voltage, surface roughness and acid resistance of the anodizing films were compared with single-layered anodizing films in sulfuric acid and oxalic acid electrolytes. Hardness of the double-layered anodizing film decreased with increasing ratio of inner layer to outer layer for both Al 5052 and Al 6061 alloys, suggesting that outer anodizing film formed in sulfuric acid electrolyte is damaged during the second anodizing in oxalic acid electrolyte. Withstand voltage of the double-layered anodizing films increased with increasing the thickness ratio of inner layer to outer layer. Surface roughness of the double-layered anodizing films were comparable with that of single-layered anodizing film formed in sulfuric acid but higher than that of single layer anodizing film formed in oxalic acid electrolyte. In acid resistance test, all of the double-layered and single-layered anodizing films showed good acid resistance more than 3 h without any visible gas evolution, which is attributable to sealing of pores. Based on the experimental results obtained in this work, it is possible to design a double-layered anodizing film with cost-effectiveness and improved physical and electrical properties by combining two consecutive anodizing processes of sulfuric acid anodizing and oxalic acid anodizing methods.

• 한국표면공학회지
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• 제52권5호
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• pp.275-281
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• 2019

Anodization is widely used to enhance the properties of aluminum, such as hardness, electric resistance, abrasion resistance, corrosion resistance etc. But these properties can be enhanced with additional process. According to the partial crystallization of oxide layer with post heat treatment, enhanced hardness can be expected with partial crystallization. In this study, post heat treatments were applied to the anodized aluminum alloys of Al6061 to achieve the partial crystallization, and crystallizations were evaluated with the reduced breakdown voltages. Interestingly, remarkable enhanced hardness (21~29%), abrasion resistance (26~62%), and reduced breakdown voltage (24~44%) were observed for the sulfuric acid anodized samples when we annealed the anodized samples with 1hour post heat treatment at $360^{\circ}C$. For the Al5052 alloys, a lot of cracks were observed when we applied the post heat treatment.

• Journal of Welding and Joining
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• 제28권6호
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• pp.70-75
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• 2010

This study intends to investigate the weldability and mechanical characteristics of butt weld joints by LAFSW for dissimilar materials (Al6061-T6 and SS400). At optimum welding conditions, the tensile strength of dissimilar materials joints made by FSW is found to be lower than that of LAFSW. Due to the increase in plastic flow and formation of finer recrystallized grains at the TMAZ and SZ by laser preheating in LAFSW, the hardness in LAFSW appeared to be higher than that of FSW. Compared with FSW, finer grain size is observed and elongated grains in parent metal are deformed in the same direction around the nugget zone in TMAZ of Al6061-T6 by LAFSW. Whereas, at weld nugget zone, coarse grain size is appeared in LAFSW compared to FSW, which is owing to more plastic flow due to laser preheating effect. In dissimilar materials joints by LAFSW, ductile mode of fracture is found to occur at Al6061 side with fewer brittle particles. Mixed mode of cleavage area and ductile fracture is observed at SS400 side.

• Journal of Welding and Joining
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• 제14권4호
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• pp.53-61
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• 1996

It was attempted to improve the wear resistance of Al alloy under the load condition by making a formation of the thicker surface hardening alloy layers. The thicker surface hardening alloy layers were formed on 6061 Al alloys overlayed by MIG and TIG welding process with Cu powders feeding. The characteristics of hardening and wear resistance have been investigated in relation to the microstructures of alloyed layers, with a selection of optimum alloying conditions for formation of overlaying layer. The results obtained were summarized as follows With increasing feeding rate of Cu powders by MIG welding, the hardness and specific wear of the overlay weld alloys were increased. It is considered that these high hardness and specific wear of overlay weld alloys were due to the formation of Θ($Al_2Cu$) phases. With increasing feeding rate of Cu powders by TIG welding, the hardness and specific wear of the overlay weld alloys were increased in feeding rates 12 and 18g/min. However, the hardness and specific wear were decreased in the powder feeding rate 38g/min. It is considered that considered that decrease of hardness and specific wear in the powder feeding rate 38g/min due to formation of ${\gamma}$($Al_4Cu_9$) phases.

• 대한기계학회논문집A
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• 제35권10호
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• pp.1145-1153
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• 2011

본 연구의 목적은 극저온 열처리를 통해 Al6061 의 열처리 잔류응력을 제거하는 것이다. 이를 위해 유한요소해석을 이용하여 열처리 잔류응력을 예측하였으며, 열처리 조건에 따른 각 단계별 대류 열전달계수를 T6 와 극저온 열처리 실험을 수행하여 결정하였다. 예측된 잔류응력 결과는 X 선회절법(XRD)으로 측정된 잔류응력 결과와 비교하여 유한요소해석 결과의 타당성을 확인하였다. 또한 T6 와 극저온 열처리에 대해 각각 전기 전도도와 경도를 측정하여 기계적 특성을 평가하고 TEM 관찰과 XRD 회절 분석을 통해 석출물의 크기 및 성분을 파악하였다. 이를 통해 Al6061 의 T6 열처리와 비교하여 극저온 열처리를 적용함에 따른 잔류응력, 기계적 특성 및 미세조직변화를 조사하였다.