NRL’s novel method of using pulsed electron beams to de-sensitized aluminum alloy on one side without inducing bulk heating (left), cross section of an eBeam treated aluminum plate with the top surface showing a de-sensitization depth of ~ 200 µm (center), and conceptual portable de-sensitization apparatus for treatment of a large plate (right).

De-Sensitization of Aluminum Alloys using Pulsed Electron Beams

The U.S. Naval Research Laboratory (NRL) has developed a new method of de-sensitizing sensitized 5XXX-series aluminum alloy plates on a single side without inducing bulk heating throughout the panel. This is accomplished by locally heating the near-surface volume to high enough temperatures (e.g., > 250 ºC) to dissolve the beta phase using pulsed electron beams. This reduces or eliminates grain boundary beta phase at the surface, where intergranular corrosion and stress-corrosion cracking occurs resulting in degraded service life of the alloy plate. This method allows for the controllable reduction in the degree of sensitization (DOS) by varying at least one of the following electron beam parameters: voltage, current density, pulse duration, pulse frequency, and total number of pulses. With an apparatus with a foil electron beam window, operation in ambient air would be possible; thus a portable eBeam system is within reason.

What is it?

A new method for de-sensitizing sensitized 5000-series aluminum alloy from a single side without heating through the entire thickness.

How does it work?

Sensitization is due to the formation of beta phase Mg2Al3 in the grain boundaries as a result of naturally occurring Mg diffusion. During the de-sensitization method, the beta phase is dissolved to a controlled depth ~200 µm while leaving the interior unaffected.

What will it accomplish?

De-sensitizing treatment before the degree of sensitization (DOS) becomes too high, reduces risk of structural degradation and can extend service-life of 5xxx alloy plate, by up to a factor of two.

Advantages

  • De-sensitized surfaces will have reduced corrosion/crack initiation rates and higher stress-corrosion cracking and corrosion-fatigue thresholds.
  • Pulsed eBeam can successfully be used to de-sensitize sensitized 5xxx aluminum alloy plates from one side without inducing heating through the thickness; thus, minimizing sensitized grain boundaries exposed to the environment, and ultimately extending time to failure and replacement.
  • Depth of de-sensitization is controlled with beam energy deposition rate and beam voltage.

Application Areas

De-sensitizing 5xxx aluminum alloy to limit corrosion and cracking to extend service-life of the metal, has prospective exterior applications where heat sensitization is a risk and superior corrosion resistance and durability are required; including both military and commercial marine vessels and structures, truck/trailer assemblies, pressure vessels, railroad cars, and fuel tanks.

Licensing and Collaboration Opportunities

US Patent No. 9,315,886 is available for license to companies with commercial interest. Collaborative research and development is available under a Cooperative Research and Development Agreement (CRADA).