In this study, we investigated the change in fracture properties after friction stir welding on Al606. In the L-T direction test, the fracture toughness of the unwelded base material was 275 MPa, and the specimen subjected to friction stir welding (FSW) was 227 MPa, showing that the fracture toughness decreased significantly with friction stir welding. In the T-L direction test, the difference between the base material and the weld material was not large, but the fracture toughness was shown to decrease during welding. In the comparison of the L-T direction and the T-L direction, it was found that both the base material and the weld material showed high fracture toughness in the L-T direction.In this study, the following conclusions were obtained after friction stir welding of Al 6061-T6.

Aluminum alloys, known for their high strength-to-weight ratios and impressive electrical and thermal conductivities, are extensively used in numerous engineering sectors, such as aerospace, automotive, and construction. Recently, significant efforts have been made to develop novel aluminum alloys specifically tailored for additive manufacturing. These new alloys aim to provide an optimal balance between mechanical properties and thermal/ electrical conductivities. In this study, nine combinatorial samples with various alloy compositions were fabricated using direct energy deposition (DED) additive manufacturing by adjusting the feeding speeds of Al6061 alloy and Al-12Si alloy powders. The effects of the alloying elements on the microstructure, electrical conductivity, and hardness were investigated. Generally, as the Si and Cu contents decreased, electrical conductivity increased and hardness decreased, exhibiting trade-off characteristics. However, electrical conductivity and hardness showed an optimal combination when the Si content was adjusted to below 4.5 wt%, which can sufficiently suppress the grain boundary segregation of the α- Si precipitates, and the Cu content was controlled to induce the formation of Al2Cu precipitates.

In this paper, the performance evaluation of Al-graphene nanoplatelets (GNP) composites surface engineered by a modified friction stir processing (FSP) is reported. Here, multiple micro channels (MCRF) are used to incorporate GNPs in the aluminium matrix instead of a single large groove (SCRF) that is usually used in conventional FSP. With the MCRF approach, ~ 18% higher peak temperature (compared to SCRF) was observed owing to the presence of aluminium sandwiched between consecutive microgrooves and higher heat accumulation in the stir zone. The MCRF approach have significantly reduced the coefficient of friction and wear rates of the processed composites by ~ 14% and ~ 57%, respectively as compared to the SCRF approach. The proposed reinforcement filling method significantly improves the particle dispersion in the matrix, which in turn changes the adhesion mode of wear in SCRF to abrasive mode in MCRF fabricated composites. The uniformly squeezed out GNP tribolayer prevented the direct metal to metal contact between composite and its counterpart which have effectively reduced the deterioration rates.

유니버설 조인트는 두 회전 축 사이에서 힘을 전달하는 구성 요소이며, 구동축과 피동축이 나란히 정렬되지 않아도 나란히 정 렬되지 않아도 동력전달이 가능하게 하며 각도 변화가 있는 전동축에서도 효율적으로 동력을 전달시키는 부품으로서 자동차의 동력전달 장치에서 많이 적용되고 있다. 차량의 경량화를 위해 고강도 알루미늄의 사용이 증가하고 있다. 본 연구에서는 알루미늄 6061 재질을 사용하여 유니버셜 조인트 샤프트를 성형하기 위해 환봉 압출, U-Shape 성형, Spline 성형 등에 대한 단조 해석 연구하였다. Bar Extrusion 성형 시 23.3Ton, U-shape 성형 시 62.2Ton, Spline 성형 시 3.2Ton, 총 Cycle Time 226sec의 성형 조건을 산출하였으며, 이를 적용하여 알루미늄 유니버셜 조인트를 제작하였다. 비틀림 시험을 통해 토크값은 평균 425.8(N・m), 비틀림 각은 평균 171.6° 의 실험값을 통해 기존 제품에 비해 단조 제품이 12.0∼14.4%의 비틀림 성능의 향상을 보였다.

In this study, Equivalent fracture strain and Fracture energy were evaluated with the small punch test(SP test) for friction stir welded(FSW) Al6061-T6 sheets. With the three rotation speeds and the three feeding rate, The nine different conditions of FSW were prepared for the SP test. The SP test specimens were manufactured and tested on the advancing side, center, and retreating side to the tool rotation direction. From the SP test data, the equivalent fracture strain and the fracture energy were analyzed. The high value of equivalent fracture strain was attained form tool rotational speed 900RPM and feeding rate 330mm/min. It is found that its characteristic is about 14% higher than the value of condition 1100RPM-330mm/min that have the lowest value. The high value of fracture energy was obtained from the tool rotation speed 900RPM and feeding rate 330mm/min. The lowest fracture energy, which from 1000RPM-300mm/min, was approximately 16% difference to the highest value.

In the present work, 6061 Al-B4C sintered composites containing different B4C contents were fabricated and their characteristic were investigated as a function of sintering temperature. For this, composite powders and their compacts with B4C various contents from 0 to 40 wt.% were fabricated using a planetary ball milling equipment and cold isostatic pressing, respectively, and then they were sintered in the temperature ranges of 580 to 660o C. Above sin- tering temperature of 640o C, real density was decreased due to the occurrence of sweat phenomena. In addition, it was realized that sinterability of 6061Al-B4C composite material was lowered with increasing B4C content, resulting in the decrease in its real density and at the same time in the increment of porosity.

A composite of rapidly solidified Al-6061 alloy powder with graphite particle reinforcements was prepared by ball milling and subsequent hot extrusion. The microstructure and mechanical properties of these composites were investigated as a function of milling time. With increasing milling time, the gas atomized initially and spherical powders became elongated with a maximum aspect ratio after milling for 30 h. Then, refinement and spheroidization were achieved by further milling to 70 h with a homogeneous and fine dispersion of graphite particles forming between the matrix alloy layers. The best compression and wear properties were obtained in the powder milled for 70 h, associated with the increased fine and homogeneous distribution of graphite particles in the aluminum alloy matrix.

In the present work, hot workability of particulate-reinforced Al6061-20%SiC composite produced by direct hot extrusion technique was studied. Uniaxial hot compression test at various temperatures and strain rates was used and the workability behavior was evaluated from the flow curves and the attendant microstructures. It was shown that the presence of SiC particles in the soft Al6061 matrix deteriorates the hot workability. Bulging of the specimens and flow lines were observed, which indicate the plastic instability during hot working. Microstructure of the composites after hot deformation was found to be heterogeneous, i.e. the reinforcement clusters were observed at the flow lines. The mechanism of deformation was found to be controlled primarily by dynamic recrystallization.

Microstructural and mechanical characteristics of P/M 6061 Al alloy subjected to equal channel angular pressing (ECAP) were investigated. The P/M 6061 Al alloy had an intial grain size of approximately . An equiaxed ultra-fine grained structure with the mean grain size of was obtained by four repetitive ECAP at 473 K. The microhardness of P/M 6061 Al alloy was drastically increased from about 40 Hv to 80 Hv by two repetitive ECAP at 373 K. However, the microhardness decreased with increasing ECAP temperature. The tensile stength of as-hot-pressed P/M 6061 Al alloy before ECAP was 95 MPa, whereas it increased to both 248 MPa after two repetitive ECAP at 373 K and 130 MPa after four repetitive ECAP at 473 K. The tensile properties of the ECAPed sample were compared with those of commercial cast 6061-O and 6061-T4 Al alloys.

The 6061 Al alloy based composites reinforced with 10 vol% SiC whiskers were prepared by powder metallurgy with the powders having the different sizes, i.e. < and> The composites were subjected to equal channel angular pressing (ECAP) at various conditions and the microstructural changes during ECAP were examined In the composites SiC whiskers were clustered and randomly aligned. The clusters were relatively well distributed in the composite with the smaller initial powder size. After ECAP, the clusters were aligned parallel to flow direction and became smaller. In addition, the shape of clusters was changed from irregular to round. The microstructure of the ECAPed samples were compared with those of the conventionally hot-extruded composites. The uniform microstructure and enhanced microhardness could be obtained by using the powders having the smaller size, decreasing ECAP temperature and repeating ECAP.

석출경화형 6061Al기지합금과 SiC입자크기를 0.7μm 및 7.0μm로 변화시켜 강화한 SiCp/6061Al 합금복합재료의 시효 거동을 경도측정, DSC 시험 및 TEM관찰을 통하여 조사하였다. 170˚C에서 등온시효시 6061Al기지합금에 비하여 복합화한 0.7μmSiCp/6061Al합금복합재료 및 7.0μmSiCP/6061Al합금복합재료에서 최고경도에 도달하는 시간이 짧았으며, 또한 강화재의 크기가 큰 7.0μmSiCp/6061Al합금복합재료에서 시효촉진이 보다 크게 나타났다. 이것은 복합화 및 SiC입자크기 증가에 따른 전위 밀도 상승에 기인한다. 6061Al기지합금 및 복합재료에서 최고시효처리시의 주강화상은 봉상의 중간상 β(Mg2Si)이며,β상 생성의 활성화에너지는 복합화 및 SiG입자크기의 증가에 따라 감소되었다