Laser Peening System to Mitigate Aluminum Stress Corrosion Cracking in Combat Ship

A $1.78 million project of the National Shipbuilding Research Program (NSRP) will fund research and development of laser peening systems by Hepburn & Sons LLC, LSP Technologies, and Vigor Shipyards to demonstrate efficient treatment of aluminum deck plates on U.S. Navy ships.

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The Naval Surface Warfare Center (NSWC) Carderock Division will provide technical expertise from the Navy to support the project.

“Contractual work based on the award began in December, following the recent project announcement. Terms include an investment of $1.96 million from the private sector team, bringing the total value of the project to nearly $3.8 million,” said LSPT VP Business Development David Lahrman.

Innovative Beam Deck Delivery System

The project will include actual installation of a Procudo^® Laser Peening System onboard a ship under repair at one of the West Coast operations of Vigor Shipyards either in Portland or Seattle. This new Beam Deck Delivery System (BDDS) will use laser peening to treat aluminum deck segments of combat ships in order to add fatigue strength to the metal. The team will use the BDDS and laser peening system to treat aluminum deck plates, both before and after welding.

Laser Peening Aluminum Plates

Many naval ships use 5xxx Series Aluminum Alloys in the ship design, making the craft lighter, stronger, and faster. However, 5xxx Series Aluminum contains Magnesium, which makes it vulnerable to sensitization at high temperatures and subsequent corrosion when the sensitized metal is exposed to saltwater.

“Sensitization of 5xxx series aluminum alloys is characterized by the gradual precipitation of the alloying element magnesium as a beta phase (Al3Mg2) along the grain boundaries after prolonged exposure to the environment. While the 5xxx alloy is corrosion resistant, these beta phases are corrosive and thus their formation increases the susceptibility of the alloy to intergranular corrosion and stress corrosion cracking.”

AIP Conference Proceedings 1806, 050001 (2017); https://doi.org/10.1063/1.4974595Published Online: 16 February 2017

Moving Beam Delivery to Treat Deck Plates

“Our company has participated in a number of defense research and development contracts, but this is the first one to include our Procudo^® Laser Peening System for a maritime application,” Lahrman said. “We’ve already demonstrated the impact of laser peening to deter stress corrosion cracking of aluminum, so now we’re working to employ a portable, hardened version of the Procudo^® systen actually onboard the ship.

“Typically, our Procudo^® installations involve robots manipulating metal parts for the laser peening process, but in this case, we will manipulate the beam delivery to the deck of the ship by using an articulating arm. This project will enable us to provide laser peening both before and after welding.”

“This project promises to be a major step forward in adopting laser peening technology to improve the survivability and reliability of Navy vessels,” said Scott Hepburn, Chief Operating Officer of Hepburn and Sons LLC. “We will validate the ways in which laser peening can improve the condition of the aluminum onboard the ship, even when the aluminum has been sensitized beyond weld repair levels. This kind of lasting repair is a high priority for the Navy.”

Laser peening may also help other welded aluminum areas onboard, as well as other metallic materials such as stainless steel water jet components and shafts, which are subject to high-frequency rotational stress and corrosive environments.