• Journal of Korea Foundry Society
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• v.41 no.5
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• pp.419-433
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• 2021

Al-Si-Cu alloys benefit from the addition of copper for better hardness and strength through precipitation hardening, which results in remarkably strong alloys. However, the addition of copper expands the solidification range of Al-Si-Cu alloys, and due to this, these alloys become more prone to hot tearing, which is one of the most common and serious fracture phenomena encountered during solidification. The conventional evaluation method of the hot tearing properties of an alloy is a relative and qualitative analysis approach that does not provide quantitative data about this phenomenon. In the present study, the mold itself part of a device developed in Instone et al. was partially modified to obtain more reliable quantitative data pertaining to the hot tearing properties of an Al-Si-Cu casting alloy. To assess the influence of Cu element, four levels of Cu contents were tested (0.5, 1.0, 3.0, and 5.0 wt.%) in the Al-Si-Cu system alloy and the hot tearing properties were evaluated in each case. As the Cu content was increased, the hot tearing strength decreased to 2.26, 1.53, 1.18, and 1.04 MPa, respectively. At the moment hot tearing occurred, the corresponding solid fraction and solidification rate decreased at the same temperature due to the increase in the solid-liquid coexistence range as the Cu content increased. The morphology of the fracture surfaces was changed from dendrites to dendrites covered with residual liquid, and CuAl₂ phases were observed in the vicinity of hot tearing.

• Journal of Korea Foundry Society
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• v.36 no.2
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• pp.67-74
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• 2016

The effects of scrap content on the hot tearing property and tensile property were investigated in AC2BS alloy. The hot tearing strengths were $16.4kgf/cm^2$, $15.2kgf/cm^2$, $14.9kgf/cm^2$ and $13.3kgf/cm^2$, respectively, under the constant solid fraction of 29.3% when the scrap contents of the specimens were 0%, 20%, 35% and 50%. In the same way, tensile strengths of the as-cast condition were $24.5kgf/mm^2$, $23.7kgf/mm^2$, $17.3kgf/mm^2$ and $16.0kgf/mm^2$, respectively, and the corresponding tensile strengths of the T6 heat treatment condition were $27.2kgf/mm^2$, $26.7kgf/mm^2$, $24.2kgf/mm^2$ and $23.9kgf/mm^2$. Hot tearing strength and tensile strength decreased as scrap content of the specimen increased. According to the evaluation of the quantitative hot tearing and tensile test results, the decrease of these strengths is due to the presence of oxide films which act as crack initiation site of the specimens. Therefore, elimination of oxide films of aluminum melt to maintain melt cleanliness is required.