Assessing and Enhancing Seawater Corrosion Performance of Aluminum Alloy 7075 and 2024 Additive Repairs Produced by Cold Gas Dynamic Spray Deposition
The purpose of this research is to investigate the corrosion behavior of cold sprayed (CS) aluminum alloys 2024 and 7075 in an immersed seawater environment, and improve understanding of CS processing-microstructure-corrosion property relationships. As a low temperature additive spray technique, CS has an attractive ability to deposit heat-sensitive alloys including AA2024 and AA7075 which is useful for additive repairs. Corrosion is a common damage mechanism which accounts for 1/5 of equipment downtime in the US military, but there is insufficient understanding of the corrosion performance of CS repair materials.This research finds that CS aluminum alloys in an immersed seawater environment can have very similar activity, reactivity, and potentiodynamic response compared to their wrought counterparts, and that CS deposits can even have superior pitting performance. CS corrosion properties, especially activity, change depending on powder heat treatment due to the resulting differences in the size and distribution of alloying element intermetallics. Solutionized CS-7075, for instance, is as active as the wrought (within margin of instrument error), but overaged CS-7075 has a less active Ecorr than wrought AA7075-T651 and in a repair scenario may cause a galvanic couple. Modifying spray processing parameters can cause significant changes in CS-2024 pitting performance without having a meaningful impact on potentiodynamic behavior. CS-7075 corrosion behavior relative to its wrought counterpart AA7075-T651 is stable for a range of electrolyte pH ( 6.2 - 8.6) and shows predictable changes in activity and reactivity that follow those observed in wrought AA7075-T651 for a range of salinity (0.5 – 1.5 times that found in ASTM D1141 artificial seawater). This results in this dissertation – the first set of comprehensive corrosion studies of CS-2024 and CS-7075 in an immersed seawater environment – highlight the promising corrosion properties of solid state repairs made from these alloys.