• 한국세라믹학회지
• /
• 제39권3호
• /
• pp.299-307
• /
• 2002

본 연구에서는 복잡 형상의 세라믹체를 효율적으로 성형할 수 있어 새로운 성형기법으로 부각되고 있는 직응집성형(Direct Coagulation Casing, DCC)공정기술에 관하여 콜로이드 계면화학을 이용하여 연구하였다. 높은 고형분량을 가지는 안정된 질화규소 슬립을 제조하기 위하여 분산제, 소결조제 그리고 응집제 각각이 다양한 공정변수에 미치는 영향에 대하여 평가하였다. 1.0 wt% Tetraethylammonium Hydroxide(TEAH)를 첨가하여 염기영역에서 소결조제를 포함한 안정된 51vol%의 질화규소 슬립을 제조할 수 있었다. 질화규소 슬립은 첨가된 $Al(CH_3COO)_2OH$의 온도증가에 따른 열분해를 이용하여 직응집성 유도하였다. 염기영역에서 $Al^{3+}$ 이온들이 aluminum hydroxide$(Al(OH)_3)$ 석출되면서 슬립내 $OH^-$ 농도를 감소시켜 질화규소 슬립을 직응집시켰다.

• 대한기계학회논문집A
• /
• 제21권5호
• /
• pp.791-799
• /
• 1997

The wear characteristics and wear mechanisms of plasma sprayed Al/sub 2/ O/sub 3/-40%TiO/sub 2/ and Cr/sub 2/O/sub 3/ deposited on casting aluminum alloy(AC4C) were investigated. Specimens were processed for various coating thicknesses. Ball on disk type wear tester was used for wear test. The scratch test on plasma sprayed coating surface showed that critical load to break the coating layer was greater than 40 N. The critical load increase with the increase of coating thickness of specimens. The friction coefficient of Cr/sub 2/O/sub 3/ coating layer was less than that of Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer. The wear resistance of Cr/sub 2/O/sub 3/ coating layer was greater than that of Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer. Microscopic observation of worn surfaces was made by SEM. SEM observation showed that the main mechanism of wear for Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer was abrasive wear under 50 N. For the case of Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer, as the surface cracks perpendicular to sliding direction propagated, the wear debris was generated in wear track. However, the main mechanism of wear for Cr/sub 2/O/sub 3/ coating layer was brittle fracture under 150 N.

• 한국주조공학회지
• /
• 제37권5호
• /
• pp.148-156
• /
• 2017

The effects of minor additives on the casting properties of AC4A aluminum alloys were investigated. Measurements of the cooling curve and microstructure observations were conducted to analyze the effects of Ti-B and Sr minor elements during the solidification process. A fine grain size and an increase in the crystallization temperature for the ${\alpha}-Al$ solution were evident after the addition of 0.1wt% Al-5%Ti-1%B additive. The modification effect of the eutectic $Mg_2Si$ phase with the addition of 0.05% Al-10%Sr additive was prominent. A fine eutectic $Mg_2Si$ phase and a decrease in the growth temperature of the eutectic $Mg_2Si$ phase were evident. Fluidity, shrinkage and solidification-cracking tests were conducted to evaluate the castability of the alloy. The combined addition of Al-5%Ti-1%B and Al-10%Sr additives showed the maximum filling length owing to the effect of the fine ${\alpha}-Al$ grains. The macro-shrinkage ratio increased, while the micro-shrinkage ratio decreased with the combined addition of Al-5%Ti-1%B and Al-10%Sr additives. The macro-shrinkage ratio was nearly identical, while the micro-shrinkage ratio increased with the addition of the Al-10%Sr additive. The tendency of the occurrence of solidification cracking decreased owing to the effect of the fine ${\alpha}-Al$ grains and the modification of the $Mg_2Si$ phase with the combined addition of Al-5%Ti-1%B and Al-10%Sr additives.

• 한국주조공학회지
• /
• 제41권6호
• /
• pp.535-542
• /
• 2021

본 연구에서는 주철-알루미늄 이종재료의 계면결합강도를 향상시키기 위하여 탈흑연 열처리를 통해 주철 표면에서 일정 깊이까지의 흑연을 제거하였다. 열처리 시간이 증가함에 따라 흑연이 제거되는 깊이는 증가하였으며, 열처리 시간과 깊이 사이에 선형 관계가 나타났다. 일정 깊이의 흑연이 제거된 주철에 알루미늄을 다이캐스팅 공법으로 주조접합하여 주철에서 흑연이 제거된 공간을 알루미늄으로 채운 후, 계면 반응 및 알루미늄 침투 깊이를 조사하고 계면접합강도를 평가하였다. 다이캐스팅 공법을 통한 알루미늄은 탈흑연 열처리된 주철 표면에서 일정한 깊이까지 채워지는 것으로 확인되었으며, 주철-알루미늄 계면에 금속간화합물이 생성되지는 않은 것으로 확인되었다. 계면접합강도는 열처리 시간과는 큰 관계없이 90MPa 수준의 접합강도를 나타내었으며 이는 탈흑연 열처리를 하지 않은 소재의 접합강도 12MPa에 비해 매우 높은 강도이며, 주철의 탈흑연 영역에서 고압 다이캐스팅 공정에 의해 침투된 알루미늄 용탕이 응고되면서 언더컷 구조의 기계적 결합에 의한 것으로 생각된다.

• 한국주조공학회지
• /
• 제15권6호
• /
• pp.566-573
• /
• 1995

In this study, the microstructural characteristics such as primary silicon, eutectic silicon, $SiC_p$ dispersion behavior, compound amount and Si solubility in $Al/SiC_p$ composite fabricated by the squeeze casting under various conditions were investigated systematically. As applied pressure(MPa) increases, cooling rate and compound amount are increased. In gravity casting, the cooling rate of hypereutectic composite is slower than of hypoeutectic composite by exothermic reaction of primary Si crystallization. But the cooling rate of hypereutectic composite is faster than that of hypoeutectic composite fabricated by same applied pressure, because amount of primary Si crystallization in hypereutectic composite was decreased, on the contrary, primary ${\alpha}-Al$ in hypoeutetic composite was increased due to increase of Si solubility in matrix by applied pressure. The crystalized primary silicon in hypereutectic composite fabricated by squeeze casting become more fine than that in non-pressure casting This is because mush zone became narrow due to increase of Si content of eutectic composition by pressure and time for growth of primary silicon got shorter according to applied pressure. It is turned out that eutectic temperature and liquidus are decreased by the increasing of squeeze pressure in all the composite due to thermal unstability of matrix owing to increasing of Si solubility in matrix by the increasing of applied pressure, as indicated in thermal anaiysis(DSC) results.

• 한국주조공학회지
• /
• 제17권4호
• /
• pp.385-392
• /
• 1997

The main objective of this study is to investigate the microstructure and tensile strength of $SiC_p$/Al alloy composites fabricated by die casting method. Die casting was performed using the preheated mold at the pouring temperature range of $620{\sim}750^{\circ}C$ under the pressure of $1,039 kgf/cm^2$. The low speed and a following high injection speed were 0.4 and 2.1 m/s, respectively. The microstructure of $SiC_p$/Al alloy composites fabricated by die casting method was found to be finer than that of composites fabricated by gravity casting. Also, SiC particulates were homogeneously distributed in refined Al matrix due to rapid solidification. The tensile strength of $SiC_p$/Al alloy composites fabricated by die casting method was found to be varied with cast temperature. The maximun tensile strength of $SiC_p$(10 vol.% and 20 vol.%)/Al alloy composites showed 380 MPa at the cast temperature of $750^{\circ}C$ and 363 MPa at the cast temperature of $700^{\circ}C$, respectively.

• 한국정밀공학회지
• /
• 제22권11호
• /
• pp.45-50
• /
• 2005

In this study, the casting/forging process was applied in manufacturing a low control arm, in order to prove that application of casting/forging process to Al6061 is likely to get the effect of light weight compared with existing steel products and to reduce the cost of materials. Firstly, In order to set up the optimum casting condition of the forging material, Al6061, casting experiments were carried out by controlling pouring temperature of the aluminum for casting, mold temperature, and pouring time. $700^{\circ}C$ pouring temperature, $300^{\circ}C$ mold temperature and 10-second pouring time were taken into account as the optimum casting conditions. With respect to a hot forging test, it is practiced on the basis of a temperature of materials, strain rate, and reduction rate so as to observe each microstructure and examine strain-stress curve simultaneously; examine tensile test and hardness test; eventually set up the optimum hot forging condition. A hot forging test, tensile test, hardness experiment, and microstructure observation were carried out on condition of $70\%$ reduction rate, $500^{\circ}C$ temperature of materials, and 1 strain rate. As a result of those experiments, 330MPa tensile strength, $16.4\%$ elongation, and 122.8Hv hardness were recorded. In oder to get a sound preform which has no unfitting cavity and less flash, two preforms were proposed on the basis of volume rate of the final product; the optimum volume rate of preform for the low control arm was $115\%$. In conclusion, it is confirmed that using the forging material rather than casting materials in casting/forging process is likely to get more superior mechanical properties. Compared with Al6061, performed by means of general forging, moreover, cast/forged Al6061 can not only stimulate productivity by reducing production processes, but cut down the cost of materials by reusing forging scraps.

• 한국산학기술학회논문지
• /
• 제20권7호
• /
• pp.347-352
• /
• 2019

본 연구는 소형 유도전동기 회전자를 생산공장에서 금형주조(die casting)로 제작 시 발생하는 cast 부 품질문제를 개선하기 위하여 수행되었다. 1차 연구결과와 현장 적용성을 고려한 수많은 parametric study를 통하여 새로운 rotor core cast model을 제안하였으며, 그 제안된 model에 대한 유효성을 평가, 검증하기 위하여 주조해석 전용프로그램을 사용한 수치해석과 실제품에 대한 현장실험을 통하여 다음과 같은 결론을 얻었다. 첫째, 유도전동기 회전자의 새로운 cast model에 대한 충진해석을 수행한 결과 용탕은 하부 end ring 부를 먼저 충진하고 이동하여 상부 end ring, core slot 부분을 충진하고 최종적으로 core slot 부분에서 충진이 완료된다. 둘째, 새롭게 제안된 rotor core cast model에 대한 용탕의 유동 양상을 보면 하부 end ring 부에 용탕의 유동에 의한 와류가 적게 발생하였으며, 현장실험 결과 하부 end ring 부 단면에서 소량의 작은 결함만이 발견되었다. 셋째, 유도전동기 회전자 제작 시 rotor core cast 형상 변경을 통하여 end ring 부 결함 발생 면적이 약 70 % 감소한 양호한 품질의 회전자를 생산할 수 있다.

• 한국주조공학회지
• /
• 제27권2호
• /
• pp.83-87
• /
• 2007

Aluminum plates of the same materials as the foam were attached by the casting process inserting the foam as a core to investigate the tensile property of open cell foams. Tensile properties of the open cell 6063 aluminum alloy foam of $10{\sim}30$ PPI were measured before and after heat treatment. Densities of test specimens were between 0.14 and $0.29g/cm^3$. Tensile strength of the 6063 aluminum foam after heat treatment showed little change. C values were in the range of $0.41{\sim}0.87$ for as cast foams and $0.11{\sim}0.27$ for T6 heat treated foams in the eq. of ${\sigma}^* _{pl}/{\sigma}_{ys}=C({\rho}/{\rho}_s)^{1.5}$, and increased with increase in the cell size.

• 열처리공학회지
• /
• 제21권6호
• /
• pp.300-306
• /
• 2008

Solid state diffusion brazing of aluminum castings (AC4C) and wrought alloys (Al6061) was conducted in order to improve thermal conductivity and temperature uniformity of the aluminum heater which was generally fabricated by casting method. Tensile strength and thermal conductivity are raised with increasing brazing temperature, obtaining 122.5 MPa and $206W/m{\cdot}K$ at $540^{\circ}C$ 5hrs brazing conditions, respectively. The diffusion brazed heater, shows maximum temperature difference of $4^{\circ}C$, exhibits a enhanced temperature uniformity compared with the cast heater having the maximum temperature difference of $11^{\circ}C$.