Friction stir processing for the reversal and mitigation of sensitisation and intergranular corrosion in aluminium alloy 5083-H321

Meredith, Gavin Simon (2014). Friction stir processing for the reversal and mitigation of sensitisation and intergranular corrosion in aluminium alloy 5083-H321. University of Birmingham. Ph.D.

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Abstract

AA5083-H321 is an aluminum alloy commonly used in ship hull superstructures as it has a corrosion resistance which affords an excellent degree of protection in chloride-rich marine environments. Corrosion performance can degrade in a process called sensitisation, due to the precipitation of a β-phase onto grain boundaries with exposure to elevated temperatures over decades of service. Friction Stir Processing (FSP) has been evaluated as a method for locally reversing the degraded microstructure and removing a susceptibility to Intergranular Corrosion (IGC) in immersed and atmospheric conditions.
Both the mechanical stirring and heat input to the plate by an FSP tool have been shown to remove the β-phase from grain boundaries which had been precipitated by a sensitisation heat treatment. Sensitisation was shown to cause intergranular corrosion of the alloy; however this susceptibility was removed after microstructural modification by FSP.
A re-sensitisation treatment of the previously sensitised and FSP’d region was seen to precipitate coarser and more discrete β-phase particles onto grain boundaries, which corroded at a faster rate than the once-sensitised material under electrochemical testing. This indicates that corrosion resistance degrades more quickly with subsequent sensitisation.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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