Shipbuilding & Aluminum Conference 2019

Presentation explains AA’s aluminum alloy and temper designation system.

Metal Preparation is one of the key steps in producing good quality welded joints. Understanding the relationship between weld preparations and avoiding weld discontinuities is one of the most important aspects of aluminum welding.

The basic history and various deviations of the Gas Tungsten Arc Welding (GTAW) process used for fusion welding of aluminum base materials. As the technology evolved, so have the adjustable parameters. A section will be dedicated to discussing new technology and the benefits that it should offer.

The speaker is Chair of the A5.10 Committee and past Vice Chair and Advisor to D1.2. We will look at how D1.2 can be used as a basis for an aluminum welding quality system. Also, he will examine some of the more recent changes to the aluminum filler metal specification AWS A5.10 latest revisions.

Some of the challenges associated with robotic aluminum welding are wire feed ability, material thickness, inconsistent parts, variable heat sinks due to part and fixture, and programming issues. The speaker will discuss the challenges in robotically welding with aluminum and how an advance in welding technology helps address them.

The most common aluminum alloys used in U.S. Navy ship construction are the marine grade aluminum-magnesium (Al-Mg) alloys due to their high strength to weigh ratio, good general corrosion, and affordability. The U.S. Navy uses Al-Mg alloys extensively throughout the fleet for primary and secondary structural applications. There is a continued demand for these alloys as there is a need for faster, smaller ships. A particular concern with the use of these alloy is sensitization. Aluminum-magnesium alloys containing more than 3.0 weight percent magnesium can become sensitized when a continuous network of β phase forms along the grain boundaries.In-service experience has shown extensive cracking in Al-Mg structures resulting from stress corrosion cracking (SCC). Stress corrosion cracking in Al-Mg can occur when the material exhibits a susceptible microstructure and is simultaneously exposed to a damaging environment and tensile stresses of sufficient magnitude. Repair welding of cracked Al-Mg proposes challenges because of the deleterious microstructure of the material.The material may contain micro-pits and/or micro defects that can entrap debris and moisture which affects overall weld quality. To address the sensitization issue and repair of cracked material, the U.S. Navy has developed relevant technologies for detection of sensitization, mitigation, and repair. Some of the technologies include the use of in-situ metallography to detect sensitized material, ultrasonic impact technology to treat the material prior to repair welding, and portable friction stir welding technology. The U.S. Navy has also developed specific requirements to ensure a high level of weld quality and minimize the need for rework. The welding requirements for welding sensitized material were developed to assist both the U.S. Navy and its contractors engaged in weld repair of aluminum superstructures.

While performing repair welding of severely damaged aluminum ship structure on Perry-Class Frigates, several breakthrough changes in welding procedures were implemented that resulted in vastly improved quality and reduction of thousands of hours of labor. These techniques have been carried forward to other applications with great success. The equipment, pre-weld and set-up tasks, and general procedures are discussed.

The presentation will provide an overview of the work performed to date to develop a portable f riction stir welder for shipboard welding of aluminum.