Observation of exothermic reaction during laser-assisted iron oxide coating on aluminum alloy

Aluminum and Fe3O4 reacts readily in what is known as thermite reaction to produce large amount of heat. Attempts were made to coat Fe-oxide on A319 cast aluminum alloy employing a high power laser to exploit this reaction. High-speed, high-resolution infrared thermography was employed to study the thermal conditions during the laser treatment. Parallel experiment using a less exothermic oxide (FeO) and the same substrate further emphasized development of higher temperature during highly exothermic reaction. The cooling rate calculated via both steady state and non-steady state relations were one order of magnitude different, which was supported by microstructural observations. Transmission electron microscopy revealed formation of aluminides as a result of reaction between iron oxide and aluminum alloys.