Kuo J H, Cheng P J, Wang H S, Hwang, W S

Abstract: This work is conducted to measure the density of A356.2 aluminum alloy with the temperature varying from 25ºC to 750ºC. Based on the Archmedes Principle, the density of the measured alloy in solid form can be derived by measuring the weight difference of a bob, which is made of the measured alloy, between immersing the bob into a liquid medium (soaking liquid) and hanging the bob in the air. To measure the alloy density in liquid form, the molten alloy is used as the soaking medium and a high melting point metal is used to make the bob. The density of the molten alloy can be derived by measuring the weight difference of the bob as it is immersed into the molten alloy in two different positions. To obtain the density of A356.2 aluminum alloy in solid form, an A356.2 aluminum alloy bob is immersed in the vegetable oil with the temperature ranging between 25ºC and 250ºC or potassium nitrite and sodium nitrite mixture with the temperature ranging between 250ºC and 600ºC. To derive the density of A356.2 aluminum alloy in molten state, a shape modified single tungsten bob, which can eliminate the potential inaccuracies caused by the high surface tension of the alloy in liquid form, is immersed into the molten A356.2 aluminum alloy. With the modified single tungsten bob method, a pretest with the density of molten pure aluminum at 670C is measured. It is observed that the measured density (2.358 g/cm3) is in good agreement with an earlier investigation (2.366 g/cm3) (Lucal, 1970). This implies that the modified setup is reliable and suitable for the application required in this study. From the measured results, the density of A356.2 aluminum alloy decreases from 2.603 g/cm3 to 2.584 g/cm3 with an increase in the temperature from 25C to 250C. Increasing the temperature from 250C to 600C, the density decreases from 2.584 g/cm3 to 2.528 g/cm3. When the temperature is above 400C, the density decreases more gradually. It is also observed that for the temperature range between 550C to 580C, which is in the two phase region of the A356.2 aluminum alloy, the density remains relatively unchanged. Increasing the temperature from 615C to 750C, the density decreases from 2.512 g/cm3 to 2.485 g/cm3.

Keywords: A356.2 aluminum alloy, Measurement of density, Modified Archmedes method.