The effect of thermal exposure on the conventional aluminium alloy 7050-T7451 and the novel alloy 7085-T651 was investigated. Engine exhaust leaks or fires could expose these airframe alloys to abnormally high temperatures, which in some cases can exceed the final ageing temperatures of these alloys. This can severely reduce the remaining life of components made from these alloys by significantly damaging their mechanical properties. The degree of thermal damage induced in aluminium alloys is time-temperature dependent; the reduction of mechanical properties increases with higher exposure temperatures and longer exposure times. This reduction is apparent both at elevated temperatures and at room temperature after exposure.

Given the above, an investigation was conducted to assess the effects of heat exposure on the static and fatigue properties of 7050-T7451 and 7085-T651. Hardness and conductivity tests of the baseline and heat-exposed materials were supported by tensile and fatigue life tests. Optical microscopy and fractographic examination were also performed. The hardness, tensile and fatigue tests indicated the mechanical strength and fatigue life were degraded by thermal exposure for both alloys. Optical microscopy of the heat-exposed material showed no apparent microstructural changes, suggesting that any such changes were below the resolution limit of the optical microscope (approximately 0.4 µm). The observed degradation of mechanical properties is of concern as it could reduce operational life and increase maintenance costs.