Effects of Mold Coating and Mold Material on the Heat Transfer Coefficient at the Casting/Mold Interface for Permanent Mold Casting of A356 Aluminum Alloy

摘要

In this study, the heat transfer coefficients, h, at the interface between A356 aluminum alloy casting and metallic mold with various coatings are measured. Two types of metallic mold; SKD-61 and FCD-500, two different coating materials; Dycote-39 (insulating type) and Al-130 (lubricating type), and three coating thicknesses for each mold/coating combination are investigated. These data are very important for mathematically modeling the solidification phenomena of the permanent mold casting. A unidirectional heat transfer system for the metallic mold casting of A356 aluminum alloy is first designed and fabricated. The designed system has the flexibility of testing different types of metallic mold, mold coolant, coating material, and coating thickness. It can also control the mold temperature, which is very essential to the permanent mold casting. Temperature measurements are then conducted with the thermocouples aligned in the casting and the metallic mold. Subsequently, the Inverse Method is employed to analyze the measured temperatures and obtain the interfacial heat transfer coefficient, h. From the measurements, it is found that for the twelve cases, when the measured h values are plotted against casting surface temperature, they can all be categorized in five stages. Also, regardless the types of mold, coating, and thickness, the interfacial heat transfer coefficient drops dramatically near 580C and eutectic temperature, 545C. For the same mold/coating combination, the value of h decreases as the coating thickness increases. For SKD-61 with Dycote-39 coating, the peak values of h near 580C; h_1, are ranged from 1,890 W/m~2 K to 840 W/m~2 K and the peak values of h near the eutectic temperature, 545C; h_3, are from 2,730 W/m~2 K for coating thickness between 43.5 mu m and 183 mu m. For SKD-61 with AL-130 coating, h_1 ranges from 1,890 W/m~2 K to 840 W/m~2 K and h_3 is from 5,880 W/m~2 K to 2,100 W/m~2 K for coating thickness between 34.6 mu m and 169.3 mu m. For FCD-500 with Dycote-39 coating, h_1 ranges from 1,689 W/m~2 K to 840 W/m~2 K and h_3 is from 2,520 W/m~2 K to 1,260 W/m~2 K for coating thickness between 51.7 mu m and 173.6 mu m. For FCD-500 with AL-130 coating, h_1 ranges from 1,470 W/m~2 K to 735 W/m~2 K and h_3 is from 1,596 W/m~2 K to 1,176 W/m~2 K for coating thickness between 40.2 mu m and 181.7 mu m. AL-130 coating has higher h than Dycote-39 for SKD-61. However, AL-130 coating has smaller h than Dycote-39 for FCD-500, SKD-61 has similar h to FCD-500 when they are both coated with Dycote-39. However, SKD-61 has higher h than FCD-500 when they are both coated with AL-130.