High Viscosity Etching Pastes for Improved NDT Methods

Nondestructive testing (NDT) is a fast way to inspect aerospace aluminum alloys (e.g. AA7XXX) to detect early signs of fatigue. Fluorescent dye penetrant is one of the most common methods of inspection for NDT of materials in the field. Aluminum must be depainted to bare metal prior to inspection. Traditional mechanical methods of depainting aluminum, such as sanding or media blasting, can obscure surface features from fluorescent dye penetrant testing. Pre-penetrant etching solutions are used to chemically etch the smeared metal from the surface prior to application of the dye penetrant. These etching solutions are low-viscosity hazardous materials making them prone to spilling. Luna Labs will develop a set of etchants that are higher viscosity, allowing them to be applied like a paste or gel to the desired etching location in any desirable orientation or configuration. Luna Labs will characterize the new etchants using multiple alloys (e.g. 7075-T6 and 7050-T7)  using mass-loss for etch rates, metallography, scanning electron microscopy, and surface profilometry analysis. These tests will prove efficacy at removing smear prior to traditional fluorescent dye penetrant inspecttion.