• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.220-225
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• 2007

The mechanical characteristics of AC4C Aluminum Casting Alloy were investigated by tensile test and impact test. Based on the tensile test' s result, we found that the yield strength of a high speed was about 10% higher than that of a low speed test and the maximum rupture strain mostly occurred in low speed tensile test. The impact energy of curved surface specimen was higher than that of plane surface specimen that can be measured in impact test.

• 한국주조공학회지
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• 제38권5호
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• pp.87-94
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• 2018

The effects of Sr and (Ti-B) additives on the tensile properties of AC4A recycled (35% scrap content) aluminum alloys were investigated. An acicular morphology of the eutectic Si phase of as-cast specimens was converted to a fibrous morphology upon the addition of Sr. Moreover, morphology of the Sr modified eutectic Si phase became finer due to a T6 heat treatment. The grain size of the ${\alpha}$-solid solution was decreased by the addition of (Ti-B) additives. Depending on the treatment conditions of the as-cast specimens, i.e., no addition, a Sr addition and a (Ti-B)+Sr addition, the tensile strength levels of the as-cast specimens were 182, 192, and 204MPa, respectively. The corresponding strengths of T6 heat-treated specimens were 293, 308, and 318MPa. Elongations of the as-cast specimens were 2.2, 3.1, and 5.6%, and the corresponding elongations of the T6 heat-treated specimens were 4.6, 6.1, and 7.6%. The percentage of the reduced section area in the tensile specimens was also increased by the Sr and (Ti-B) additives. Sr and (Ti-B) additives changed the microstructure and the distribution of defects in the castings, resulting in an improvement of the tensile properties of AC4A aluminum alloys. According to our test results, recycled (35% scrap content) AC4A aluminum alloy met all of the KS requirements of the tensile strength and elongation values of AC4A aluminum alloy except for the elongation value of the one specimen condition, in this case the as-cast no-addition condition.

• 한국주조공학회지
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• 제39권4호
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• pp.61-74
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• 2019

The effects of Sr and (Ti-B) additives on the impact and fatigue properties of recycled (35% scrap content) AC4A aluminum alloy are investigated here. The acicular morphology of the eutectic Si phase of as-cast specimens was converted to the fibrous one with Sr additives. The grain size of the α-solid solution decreased by the addition of (Ti-B) additives. The crack initiation energy (E_i) of the impact absorption energy decreased due to the incorporation of an oxide film and inclusions depending on the scrap used. The modification of the eutectic Si morphology by Sr additives is considered as the main factor of the increase of the average impact absorption energy (E_t). The addition of (Ti-B) additives contributed to an increase in the occurrence of crack deflections due to the refining of α-Al grains, resulting in improved fatigue properties.

• 한국주조공학회지
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• 제38권2호
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• pp.41-47
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• 2018

In a numerical study, equations relating the mechanical properties and cooling rate in a casting process have been applied to an AC4CH cast aluminum alloy. Good agreement was found between the measured and predicted material properties. Step-shaped steel blocks were made to comprise a casting mold with a Y-shaped cavity. Thermometers were inserted into each step of the mold to investigate temperature changes. The microstructure and mechanical properties, such as hardness and tensile stress were measured for each cut of piece. The correlation between the cooling rate and SDAS was found by curved fitting. Moreover, both the solidification time and the temperature were simulated using a commercial package, ZCast. The simulation results for yield strength, tensile strength, elongation, and hardness were compared with experimental results. Using the estimated K and n values, the hardness values of a ship propeller were simulated, and the results were similar to those obtained for actual castings.

• 한국주조공학회지
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• 제40권3호
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• pp.85-96
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• 2020

The effect of an aluminum scrap addition ratio on the tensile and solidification cracking properties of the AC4A aluminum alloy in the as-cast state and heat-treated state were investigated in this study. Generally, the expected problem of using scrap in aluminum casting is an increase of hydrogen and Fe element inside the aluminum melt. Another issue is an oxide film which has a weak interface with the molten aluminum and acts as potent nucleation sites for internal porosity and crack initiation. Solidification cracking is one of the critical defects that must be resolved to produce high quality castings. A conventional evaluation method for solidification cracking is a relative and qualitative analysis method which does not provide quantitative data on the thermal stress in the solidification process. Therefore, a newly designed solidification cracking test apparatus was used in this study, and the device can provide quantitative data. As a result, after conducting experiments with different scrap addition ratios (0%, 20%, 35%, 50%), the tensile strengths and elongations in the as-cast state were 214, 187.7, 182.1 and 170.4MPa and 4.6%, 3.4%, 3.1% and 2.3%, respectively. In the case of the T6 heat-treated state, the tensile strengths and elongations were 314.9, 294.6, 293.1 and 271.1MPa and 5.4%, 4.6%, 3.8% and 3.1%, respectively. The strength of the solidification cracking was 3.1, 2.4, 2.2and 1.6MPa as the scrap addition ratio increases.

• 동력기계공학회지
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• 제20권5호
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• pp.29-36
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• 2016

Aluminum alloys have been widely used in engine materials, cold & hot-water storage vessels and piping etc., Furthermore, the aluminum alloy of AC8A have been widely used in mold casting material of engine piston for various vehicles because of its properties of temperature, wear and corrosion resistance. Therefore, it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and to prolong its lifetime. In previous paper, the effect of solution($510^{\circ}C$:4hrs) and tempering($190^{\circ}C$: 16, 24, and 36 hrs)heat treatments to corrosion resistance and hardness were investigated using electrochemical method. In this study, in order to examine completely the effect of the tempering hours to hardness variation and corrosion resistance, the results of solution($510^{\circ}C$:4hrs) and tempering($190^{\circ}C$: 2, 4, 8 and 12hrs)heat treatments to hardness and corrosion resistance were investigated using electrochemical method. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment. Furthermore, the corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. And the tempering heat treatment temperature at $190^{\circ}C$ for 8 hrs exhibited the highest value of the hardness and also indicated the highest corrosion current density. However, the values of hardness and corrosion current density was again increasingly decreased with increasing of tempering hours than 8 hrs, Consequently, it is suggested that decision of the optimum. tempering hours is very important to improve the corrosion or wear resistance.

• 한국해양공학회지
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• 제22권5호
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• pp.106-111
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• 2008

In this paper, study about property evaluation for the metal matrix composites fabricated by low pressure infiltration process. Aluminum alloy composite which is reinforced by Metal fiber preform was fabricated by low pressure casting process. Infiltration condition was changed the pressure infiltration time of 1 sec, 2 sec and 5 sec under a constant pressure of 0.4 MPa. The molten alloy completely infiltrated the FeCrSi metal perform regardless of the increase in the pressure acceleration time. The the porosity in the FeCrSi/AC8A composite was investigated. The porosity was reduced as the pressure acceleration time as shorter. The FeCrSi/AC8A composite was investigated the wear test for to know the relationship between Porosity and wear resistance. FeCrSi/AC8A composite at pressure acceleration time of 1sec is shown excellent wear resistance.

• 한국주조공학회지
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• 제30권5호
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• pp.174-178
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• 2010

In the present study, in-situ real-time observation with an X-ray radioscopic facility was carried out on pure aluminum and aluminum alloy solidification. The three kinds of aluminum alloys, such as pure aluminum, Al-8.5%Si alloy, commercial A356 (AC4C) alloys, were used in the present study. The formations of the shrinkage defects in the castings were visualized and different formation phenomena for different aluminum alloys were investigated.

• 한국주조공학회지
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• 제13권4호
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• pp.369-381
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• 1993

Aluminum alloy(AC8A) matrix composites reinforced with SiC particles(10% in vol.) were fabricated by Centrifugal Spray Deposition(CSD) process. The microstructures were investigated in order to evaluate both the mixing mode between aluminum matrix and SiC particles, and the effect of SiC particles on the cooling behaviours of droplets during flight and preforms deposited. A non-continuum mathematical calculation was performed to explain and to quantify the evolution of microstructures in the droplets and preforms deposited. Conclusions obtained are as follows; 1. The powders produced by CSD process showed, in general, ligament type, and more than 60% of the powders produced were about 300 to 850 um in size. 2. AC8A droplets solidified during flight showed fine dendritic structure, but AC8A droplets mixed with SiC particles showed fine equiaxed grain structure, and eutectic silicon were formed to crystallize granularly between fine aluminum grains. 3. SiC particles seem to act as a nucleation sites for pro-eutectic silicon during solidification of AC8A alloy. 4. The microstructure of composite powders formed by CSD process showed particle embedded type, and resulted in dispersed type microstructure in preforms deposited. 5. The pro-eutectic silicon crystallized granularly between fine aluminum grains seem to prohibit grains from growth during spray deposition process. 6. The interfacial reactions between aluminum matrix and SiC particles were not observed from the deposit performs and the solidified droplets. 7. The continuum model seem to be useful in connecting the processing parameters with the resultant microstructures. From these results, it was concluded that the fabrication of aluminum matrix composites reinforced homogeneously with SiC particles was possible.

• International Journal of Precision Engineering and Manufacturing
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• 제6권3호
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• pp.56-59
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• 2005

Aluminum alloy casting is gaining increased acceptance in automotive and electronic industries and especially, squeeze casting is the most efficient method of mass manufacturing of such parts. In this study, the microstructures and mechanical properties of Al-7.0Si-0.4Mg(AC4C) alloy fabricated by squeeze casting process for development of fuel system parts (fuel rail) are investigated. The microstructure of squeeze cast specimen was composed of eutectic structure aluminum solid solution and $Mg_2Si$ precipitates. The tensile strength of as-solid solution treatment Al-7.0Si-0.4Mg alloy was 298.5MPa. It was found that Al-7.0Si-0.4Mg alloy had good corrosion resistance in electrochemical polarization test.