Application of infrared imaging in optimizing the induction heating of semi-solid aluminum alloys

Semi-solid die casting provides an interesting alternative to the conventional die casting technique as components produced have typically very few defects and can be heat treated to enhance mechanical properties. In this technique, the metal is first heated in an induction furnace until it reaches the semi-solid state (partially liquid and partially solid). It is then injected into a die and kept there until it is solidified. Subsequently, the die opens, the part is ejected and the cycle starts again. In this work, infrared thermography is used to evaluate and optimize the heating system in semi-solid aluminum die casting. The liquid/solid fraction and its spatial distribution are crucial for the process. An accurate control of the temperature readings as well as the identification of the thermal gradients during the heating cycle are therefore necessary. With infrared thermography, it is possible to measure the temperature distribution on the entire surface. This technique has the advantage of providing high-resolution temperature cartography as well as information on how thermal energy is dissipated. However the time variation in surface emissivity caused by aluminum oxidation makes the absolute temperature measurement difficult. A high emissivity flat black paint is used to overcome this problem and make thermal imaging reliable. The effects of power level and power input profile on the temperature distribution and heating cycle time are considered. (author)