| Corrosion in Aluminum
Studies at Vanderbilt have demonstrated that superconducting quantum interference (SQUID) magnetometers can be utilized for quantitative measurements of hidden corrosion activity in aircraft aluminum alloys. SQUIDs may offer the best method for quantitative, laboratory assessment of the rate of hidden corrosion in aircraft samples in various environments.
In contrast to conventional electrochemical techniques, SQUIDs can:
- non-invasively detect hidden corrosion activity at the very onset of corrosion,
- detect hidden corrosion long before other less sensitive techniques can, and
- provide information in real time that would otherwise require lengthy exposure to the corrosive environment or the use of procedures that accelerate corrosion.
Our group has developed instrumentation and recording and analysis techniques that are optimized for the measurement of the spatial and temporal dependence of the magnetic fields associated with hidden corrosion in lap joints.
The corrosion system, shown schematically in Figure 1, was designed and assembled at Vanderbilt. It includes:
- a three-axis vector gradiometer,
- a three-layer magnetic shield,
- a scanning stage with a custom sample-handling system,
- a computer control system, and custom scanning and analysis software.
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The AFCO/NCI SQUID system
for laboratory measurements of corrosion activity in aircraft aluminum.
A cross-sectional drawing of the entire system.
The cylindrical magnetic shield and stage system (in the background) at the Vanderbilt Electromagnetics Laboratory.
The top of the stage where the sample is placed on the diving board and carried through the shield.
A view from the access port of the shield, showing the tip of the cryogenic dewar (blue cylinder) where the pickup coil is located, the sample holder and the glass-topped support table.
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Our current work indicates there is a clear need to determine the factors that govern the relationship between the electrical currents produced by hidden corrosion activity and the associated magnetic field.
Our future work will be directly applicable to the use of SQUIDs to quantify the spatial extent and instantaneous rate of hidden crevice corrosion in aircraft lap joints and intergranular corrosion in thick wing planks.
A. Abedi, J.J. Fellenstein, A.J. Lucas and J.P. Wikswo, "A SQUID
magnetometer system for quantitative analysis and imaging of hidden corrosion activity in aircraft aluminum structures" Rev. Sci. Instr., 70 (12) 4640-4651 (1999).
Afshin Abedi, Grant Skennerton, John Wikswo, "SQUID
magnetometers for quantitative measurements of rate and imaging of hidden
corrosion", CORROSION NACExpo 99, paper number 918, San Antonio, Texas, on
April 25-30, 1999.
G. Skennerton, A. Abedi, R.G.
Kelly, and J.P. Wikswo, Jr., “Magnetic
Measurements of the Response of Corrosion Activity within Aircraft Lap Joints
to Accelerated Corrosion Testing”, The Journal of Corrosion Science and
Engineering, 2000, vol. 3, paper 2.
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