• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.10a
• /
• pp.193-197
• /
• 2002

In this study, the casting/forging process was applied to the Shift-Fork, a manual transmission part of automobiles. In the casting experiments, the effects of additives, Sr, Ti＋B and Mg, on the mechanical properties and the microstructure of a cast preform were investigated. When 0.03% Sr were added into the molten aluminum alloy, the finest silicon-structure was observed in the cast preform and the highest tensile strength and elongation accomplished. And when 0.2% Ti＋B were added into the molten Al-Si alloy, the highest values of tensile strength were obtained. The maximum hardness was in case of 0.2% Mg. In the forging experiment, it was confirmed that the optimal configuration of the cast preform could be predicted by FE analysis. To minimize the cost as the press size, the compact shape of preform was proposed to reduce the volume of flash. The modification of shape in designing preform was performed to attain a satisfactory performance in the areas where the mechanical strength were more required. By using FVM(Finite Volume Method) software, it was verified that a proposed casting design was available. To identify the relationship between effective strain and mechanical properties of the final forged product, the compression test was performed. As the result, the tensile strength and elongation of a cast preform were much higher than before forging. The minimum forging temperature was found 40$0^{\circ}C$ to save heating time.

• Journal of the Korean institute of surface engineering
• /
• v.23 no.1
• /
• pp.34-43
• /
• 1990

Al-Si piston alloys such as AlS10CuMg have been anodized to examine apossibility of forming a hard film aat relatively higher temperatures compard with those in conventional sulfuric acid processes. Three types of electrolytes have been employed in this study ; electrolyte A(15% H2SO4, $0^{\circ}C$), electrolyte B(12% H2SO4, 1% oxalic, $10^{\circ}C$), electrolyte C(tartaric acid 125g/L+oxalic 75g/L+aluminum sulfate 225g/L, $25^{\circ}C$). Hard anodisine process in electrolyte B at a current density of 1.54A/dm2 produced a harder film of VHN 396 at a relatibely low film forming voltage compared with those obtained in other electrolyte at equivalent current density. A liner relationship between hardness and abrasion resistance exists for Al-Si piston alloys. The hardness of anodized film decreasees with increasing silicon content in Al-Si alloys and also with bath temperature. The film hardeness of Na-modified alloy os higher than that of P-modified alloy due to its finer microstructre. The film on the silicon phase in Al-Si alloys is observed to be formed by lateral growth of oxide film nucleated at surroundings.

• Journal of Korea Foundry Society
• /
• v.15 no.6
• /
• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1997.06a
• /
• pp.160-173
• /
• 1997

Microstructure of hypereutectic Al-17wt.% Si alloy, fabricated by mechanical stirring and by reheating at semi-solid state, was investigated by optical microscope. Flow behavior semi-solid metal also was investigated at diffentent mould temperatures 280$^{\circ}C$, 290$^{\circ}C$ and 300$^{\circ}C$. Size of silicon particles were increased over 100$\mu\textrm{m}$ during solidification as a result of stirring. It is considered as microstructural coarsening by bonding between neighbouring primary silion particles during stirring of slurry. In case of reheating at semi-solid state, however, primary silicon particle was not increased at size of 40$\mu\textrm{m}$ and nearly spherical aluminum solde particle also could be obtained uniformly in distribution. The fludity of Al-17wt.% Si alloys at semi-solid state was improved when solid fraction was 0.7 at mould temperature of 300$^{\circ}C$ than other conditions.

• Journal of Korea Foundry Society
• /
• v.30 no.4
• /
• pp.151-156
• /
• 2010

The high-strength low-alloy (HSLA) steels have low carbon contents (0.05~0.25% C) in order to produce adequate formability and weldability, and they have manganese contents up to 1.7%. Small quantities of silicon, chromium, nickel, copper, aluminum, molybdenum are used in various combinations. The results contained in this paper can provide the valuable information on the development of $-40^{\circ}C$ low temperature HSLA. Furthermore, the present experimental data will provide important database for casting steel materials of the offshore structure.

• Journal of the Society of Naval Architects of Korea
• /
• v.45 no.4
• /
• pp.426-431
• /
• 2008

The high-strength low-alloy(HSLA) steels have low carbon contents($0.05{\sim}0.25%$ C) in order to produce adequate formability and weldability, and they have manganese contents up to 1.7%. Small quantities of silicon, chromium, nickel, copper, aluminum, molybdenum are used in various combinations. The results contained in this paper can provide the valuable information on the development of $-40^{\circ}C$ low temperature HSLA. Furthermore, the present experimental data will provide important database for casting steel materials of the offshore structure.

• Korean Journal of Metals and Materials
• /
• v.48 no.1
• /
• pp.49-56
• /
• 2010

This study investigated how the surface of Al-12wt.%Si alloy modified by the plasma electrolytic oxidation process (PEO). The PEO process was performed in an electrolyte with sodium hexametaphsphate as a conducting salt, and the effect of ammonium metavanadate on variations in the morphology of electrochemically generated oxide layers on the alloy surface was investigated. It is difficult to form a uniform passive oxide layer on Al alloys with a high Si content due to the differences in the oxidation behavior of the silicon-rich phase and the aluminum-rich phase. The oxide layer covered the entire surface of the Al-12WT.%Si alloy uniformly when ammonium metavanadate was added to the electrolyte. The oxide layer was confirmed as a mixture of $V_2O_3$ and $V_2O_5$ by XPS analysis. In addition, the oxide layer obtained by the PEO process with ammonium metavanadate exhibited a black color. Application of this surface modification method is expected to solve the problem of the lack of uniformity in the coloring of oxide layeres caused by different oxidation behaviors during a surface treatment.

• Journal of Korea Foundry Society
• /
• v.34 no.4
• /
• pp.130-135
• /
• 2014

Efforts have been made to develop new silicon-free aluminum casting alloys that possess high electrical and thermal conductivity. In this research Al-Fe-Cu-Mg alloys with various Cu and Mg contents were investigated for their various properties. As the Cu or Mg content was increased, the electrical conductivity gradually decreased, while the tensile strength of the Al-Fe-Cu-Mg alloy tended to be improved. It was found that fluidity was generally inversely proportional to the Cu content, but the alloys containing 1%Mg showed considerably low fluidity, regardless of the Cu content.

• Journal of the Korean Society for Heat Treatment
• /
• v.9 no.3
• /
• pp.161-168
• /
• 1996

The purpose of this study is to investigate the effect of impurity level and fabrication processes on the strength, fracture toughness and fatigue resistance of 7075, 7050 and 7175 high strength aluminum forgings. It has been verified that plane strain fracture toughness and fatigue characteristics of a specially processed 7175S-T74 alloy is superior to a conventionally processed 7075-T6/T73, 7050-T74 and 7175-T74 alloys. These beneficial effects primarily arise from two view points, i.e., the effect of reducing the impurity level of iron and silicon has significantly diminished the size and volume fraction of second phase particles such as $Al_7Cu_2Fe$ and $Mg_2Si$. Futher reduction of the amount of nonequilibrium second phase particles has been observed by applying a special fabrication process.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.10
• /
• pp.2034-2043
• /
• 2002

The process design to produce a near net shape home-appliance compressor component using semi-solid die casting process is performed. In order to obtain a good component without defects such as liquid segregation and porosity, the relationship between pressure and time, and plunger tip displacement and injection velocity are proposed with repeated trial and error. The effect of the velocity variation in the process parameters on liquid segregation and extraction is investigated to produce the aluminum frame part(a kind of compressor part) with good mechanical properties. The mechanical characteristic of semi-solid die casting formed parts for AlSi7Mg0.65r(A357) and AlSi17Cu4Mg(A390) are investigated with a view to minimizing the occurrence of defects. To investigate of application possibility at industry field, A380 aluminum alloy with 8∼9% silicon contents used for the squeeze casting process. The obtained mechanical properties is compared with semi-solid die casting.