Heat Transfer Simulation to Determine the Impact of Al-5Mg Arc Sprayed Coating onto 7075 T6 Al Alloy Fatigue Performance

Aluminum-5% magnesium coatings was deposited by arc spraying onto aircraft Al 7075 T651 structural alloy for corrosion protection while required to maintain the substrate material fatigue performance integrity. Fatigue performance of coating system is complex and in order to better understand the variability of the fatigue performance of coatings, heat flow in substrate was studied and simulated to determine the temperature evolution during arc spraying in both substrate and coating for different process parameters. Experimental temperature measurements, theoretical calculations and simulation were carried out to extrapolate the coating temperature with respect to coating process variables and surface preparation. Both flux and conductance were identified by an inverse method to reproduce experimental temperature measurements. The thermal transient solver of LS-DYNA® was used to simulate the time-dependence of heat flux in the coating during successive depositions. The benefit of that model is its capability to predict the temperature distribution and evolution in time in a sample. Samples were made of Al 7075 T651 alloy and were 80 mm in length by 25 mm wide and 7 mm thick. A coating thickness of 250 μm was reached. It was the spray thermal energy that was taken into account in the model as the thermal load. The quality of the thermal contact between the substrate and coating was also included in the model and conductance was defined to control the amount of heat transferred at the interface. Coating performance was evaluated in term of fatigue properties, bond strength, and interface quality of as deposited coatings. The superior fatigue resistance of the coated alloy relies on low heat input process parameters and surface preparation that favor high interface conductance to keep low coating temperature during the coating process. Surface preparation, arc current and atomizing gases play all a key role to provide a fatigue resistant coating.