• 소성∙가공
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• 제16권3호
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• pp.178-186
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• 2007

Rheo-forging process of aluminum alloy is suitable for large parts of net shape without defects and excellent mechanical properties in comparison with conventional die casting and forging process. To control the microstructure of the product with high mechanical properties in rheo-forming, solid fraction is required to prevent porosity and liquid segregation. Therefore, in rheo-forging process, die shape, pressure type and solid fraction are very important parameters. The defects such as porosity, liquid segregation and unfitting phenomena occur during rheo-forging process. To prevent these defects, mechanical properties and microstructure analysis of samples versus the change of pressure are carried out and the problem and its solutions are proposed. Also, the mechanical properties versus various pressures were compared with and without heat treatment. The alloys used for rheo-forming are A356 and 2024 aluminum alloy. The rheology material is fabricated by electromagnetic process with controlling current and stirring time.

• 대한금속재료학회지
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• 제49권9호
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• pp.686-691
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• 2011

To develop creep resistant die-cast Mg alloys, various alloying elements, including Ca, Ce, and Sr, were added to a Mg-Al alloy. The AXE710 alloy was produced on a 320 ton high-pressure die casting machine. The microstructure and creep properties of the alloy were examined. The creep behavior was investigated at $150^{\circ}C$ for stresses ranging from 50 to 100 MPa. The stress exponent was derived from the relationship between normalized secondary creep rates and compensated effective stresses. It was found to be 4.9, indicating that the dislocation climb is a dominant creep mechanism.

• 한국기계가공학회지
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• 제14권5호
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• pp.1-7
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• 2015

Cleaning by injecting dry ice and water is a generally adopted trend these days to clean molds (injection, diecasting foundry, press, rubber mold, etc). This cleaning method is performed manually, or by installing multiple high pressure spray nozzles. We have manufactured a turbine cleaning module device that is able to clean diecasting modules at any position and angle in the space by mounting an articulated robot instead of the existing pipe type injection nozzle, to minimize lead time and enhance working yield of the cleaning process. In this paper, we analyzed process factors that are required to design the turbine module by reviewing number of revolution, and results according to different blade angles and thicknesses of the mold release injection turbine module, using computational fiuid dynamics (CFD).

• 한국주조공학회지
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• 제41권6호
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• pp.535-542
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• 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
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• 제31권4호
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• pp.198-204
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• 2011

The present study was aimed to investigate the dependence of fatigue property on microporosity variation of low-pressure die-cast (LPDC) A356 alloy. The fatigue property of A356 alloy was evaluated through high cycle fatigue test, and the microporosity-terms used were the fractographic porosity measured from SEM observation on fractured surface and the volumetric porosity obtained through the density measurement using Archimedes's principle. The number of cycles to failure of A356 alloys depends obviously upon the variation of fractographic porosity, and can describe in terms of the defect susceptibility which depends on the microporosity variation at a given value of stress amplitude. The modified Basquin's equation was suggested through the combination of microporosity variation and static maximum tensile stress to fatigue strength coefficient. Using modified Basquin's equation, it could suggest that the maximum values of fatigue strength coefficient and exponent achievable in defect-free condition of A356 alloy are 265 MPa, -0.07, respectively.

• 한국자동차공학회논문집
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• 제18권1호
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• pp.120-126
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• 2010

It was known that the excellent wear resistance of hyper eutectic aluminum alloy is based on the primary Si particles which are distributed in the base metal. When the primary Si volume fraction increases, the smaller size have excellent wear resistance characteristics. However, this trend always does not match. There is no investigation result based on the materials and methods for real using parts. In this study, using the automotive parts manufacturer currently in use hyper eutectic Al alloy tensile test specimen type sample was fabricated by 350Ton high pressure die-casting machine. Then, fluidity, tensile, impact and wear resistance properties were evaluated. If the casting quality, primary Si size, fraction and distribution are similar, mechanical properties and wear resistance are equivalent.

• 한국정밀공학회지
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• 제20권2호
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• pp.58-65
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• 2003

The conventional forming process such as squeeze casting or die casting for fabricating metal matrix composites products have a disadvantage such as non homogenous distribution of reinforcement, weak bonding between matrix and reinforcement and cost increase in parts fabrication. Thixoforming process has been accepted as a new method for fabricating the net shaped metal matrix composites with lightweight and wear resistance. In this paper, the effect of volume fraction and reinforcement sizes on mechanical properties in cylinder liner part of metal matrix composites has been investigated with processes parameters such as pressure and velocity. Moreover, the methods to obtain the thixoforged composites cylinder liner with high quality has been proposed. To evaluate the composites cylinder linear fabricated at the conditions proposed in this study, mechanical properties of fabricated composites cylinder linear were compared with those of commercial composites cylinder linear.

• Corrosion Science and Technology
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• 제16권3호
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• pp.100-108
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• 2017

In this investigation corrosion behavior of newly developed high-pressure die cast Al-Ni (N15) and Al-Ni-Ca (NX1503) alloys was studied in 3.5% NaCl solution. The electrochemical corrosion behavior was evaluated using open circuit potential (OCP) measurement, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization results validated that NX1503 alloy exhibited lower corrosion current density ($i_{corr}$) value ($5.969{\mu}A/cm^2$) compared to N15 ($7.387{\mu}A/cm^2$). EIS-Bode plots revealed a higher impedance (${\mid}Z{\mid}$) value and maximum phase angle value for NX1503 than N15 alloy. Equivalent circuit curve fitting analysis revealed that surface layer ($R_1$) and charge transfer resistance ($R_{ct}$) values of NX1503 alloy was higher compared to N15 alloy. Immersion corrosion studies were also conducted for alloys using fishing line specimen arrangement to simultaneously measure corrosion rates from weight loss ($P_W$) and hydrogen volume ($P_H$) after 72 hours and NX1503 alloy had lower corrosion rate compared to N15 alloy. The addition of Ca to N15 alloy significantly reduced the Al3Ni intermetallic phase and further grain refinement may be attributed for reduction in the corrosion rate.

• 소성∙가공
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• 제14권3호
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• pp.224-232
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• 2005

The high-pressure die-casting is one of the most effective methods to produce a large amount of products in short cycle time. This process, however, has a problem that the gas porosity defect appears easily. The generation of gas porosity is known mainly due to the air entrapment during the injection stage. Most of numerical simulations for the molten metal flow pattern observations have done in the treating of one phase fluid flow but the gas-liquid interface is essentially multi- phase phenomenon. In this paper, the two-phase fluid flow numerical simulation methods have been adapted to predict the gas porosity generations in the molten metal. The accuracy and the usefulness of the new simulation module have been emphasized and verified through some comparison experiments.

• 한국주조공학회지
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• 제31권1호
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• pp.18-25
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• 2011

Effect of Fe and Mn contents on the tensile properties has been studied in Al-9wt%Si-0.3wt%Mg alloy. As Fe content of Al-9wt%Si-0.3wt%Mg-0.5wt%Mn alloy increased from 0.15wt% to 0.45wt%, tensile strength of as-cast alloy decreased from 192 MPa to 174 MPa, and elongation of the alloy also decreased from 4.8% to 4.2%. Decrease of these properties can be explained as the formation of plate shape, ${\beta}-Al_5FeSi$ phase with high Fe/Mn ratio of the alloy. However when Mn content of Al-9wt%Si-0.3wt%Mg-0.45wt%Fe alloy increased from 0.3wt% to 0.5wt%, tensile strength of T6 aged alloy increased from 265 MPa to 275 MPa, and elongation of the alloy increased from 2.3% to 3.6%. These improvements attribute to chinese script, ${\alpha}-Al_{15}(Mn,Fe)_3Si_2$ phase shape-modified from ${\beta}-Al_5FeSi$ phase with low Fe/Mn ratio of the alloy.