Abstract
The present study investigated the effect of the casting conditions for the reduced pressure test (RPT) on the melt quality of Al-Si alloy. The casting conditions considered in RPT were the atmospheric exposure during melting, sampling method, and mold pre-heating temperature. Density Index (DI) was measured to quantify the melt quality of the Al-Si alloy casted with the different casting conditions for the RPT. The sample with blocking atmospheric exposure during melting was 5.6% lower in DI than the one without blocking. DI showed a 1.9% gap between scooping-out and pouring sampling methods. Increasing mold pre-heating temperature from 100 °C to 250 °C increased the DI of the alloy from 8.5% to 18.7%. On the other hand, when the mold pre-heating temperature was 350 °C, the DI of the alloy dropped sharply to 0.9%. The melt quality of the alloys was analyzed by measuring the pores and microstructure and simulating the solidification of the samples. It was presumed that the oxides and inclusions in the molten alloys caused the difference in DI according to the atmospheric exposure and the sampling method. The difference in DI according to the mold pre-heating temperature could be understood by calculating the solidification starting time and hydrogen diffusion coefficient during the solidification of the alloys in RPT.
Highlights
In line with international environmental regulations that have recently been reinforced, Al alloy-based weight lightening studies have been on the rise in transportation industries, including automotive and aircraft industries [1,2,3,4,5,6]
In the reduced pressure test to see the effect of atmospheric exposure during melting, the samples Al_b and Al_nb showed the Density Index (DI) of 2.9 and 8.5%, respectively (Figure 3a)
Regarding the effect of atmospheric exposure, it is speculated that blocking atmospheric exposure to the crucible restricts oxides from forming on the surface of Al melt and limits the amount of gas dissolving into the melt, enhancing the quality of the melt
Summary
In line with international environmental regulations that have recently been reinforced, Al alloy-based weight lightening studies have been on the rise in transportation industries, including automotive and aircraft industries [1,2,3,4,5,6]. Aluminum usage in the automotive industry has steadily increased since the 1970s, when cylinder and other engine parts began to use Al alloys in an attempt to raise fuel efficiency and reduce exhaust emissions; and, with the transition from internal combustion engine to electric drive system, aluminum demand for the auto frame is expanding in order to balance heavier vehicle weights. Al cast alloy products in general have internal defects, such as cracks, pores, shrinkage cavities, and inclusions. These defects come variously from hydrogen gas, oxides, intermetallic compounds, and segregation [10,11]. The oxide film on the surface of and inclusions in the molten
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