Two mechanistically different modes of EIC have been identified using high-resolution X-ray computed tomography and scanning electron microscopy (SEM) in sensitized AA5083-H131 that had been pre-exposed to 0.6 M NaCl prior to interrupted slow strain rate testing (SSRT) in the short transverse direction while exposed to laboratory air (50% RH). One mode, shown to propagate when local stress intensity factors are in the range of 4–12 MNm‐3/2, is the well-known ‘classic’ form of intergranular stress corrosion cracking, Type-1 cracking, which would not initiate and propagate in dry air, irrespective of pre-exposure or sensitization. The second mode of cracking, identified presently as Type-2 cracking, is associated with sudden load-drops occurring after the UTS during SSRT. Type-2 cracking propagates at higher local stress intensity factors (above 12–15  MNm-3/2) with significantly higher average growth rates than Type-1 cracking, involves the sudden simultaneous mechanical linkage of multiple fully-isolated regions of damage, pre-determined during pre-exposure to NaCl solution and generated during straining in laboratory air. Differences in the extent of Type-2 cracking for pre-exposed samples tested in ‘dry’ air compared to laboratory air (50% RH) were marked, with that in dry air being limited to isolated patches. High-resolution 3D tomography and detailed SEM has been used to distinguish these two mechanistically different modes of EIC. Implications for a role of hydrogen embrittlement during EIC are discussed.

Improved understanding of environment-induced cracking (EIC) of sensitized 5XXX series aluminium alloys

The effect of reversion heat treatment on the degree of sensitisation for aluminium alloy AA5083

Plasma-MIG (metal inert-gas) hybrid welding is an advanced welding technology of aluminum alloys, which integrates the advantages of deep penetration in plasma arc welding and excellent filling ability in MIG welding. In this paper, the 5083 aluminum alloy plates with 6-mm thickness were welded using paraxial plasma-MIG hybrid welding. The influence of processing parameters such as the welding speed, plasma current, MIG current, and plasma gas flow rate on the weld forming was investigated, and the microstructure and mechanical behavior of welded joint under the typical parameters were studied. Both the penetration depth and weld width decreased with the increase of welding speed, increased with the increase of MIG current. While plasma arc current and plasma gas flow rate mainly affected penetration depth. The welding joint underwent the different thermal cycles in the different regions, which resulted in the different microstructure. Compared with the lower part of welding joint, the secondary phases in the upper part were bulkier and the dendrite arm spacing was wider, and the width in the partially melted zone (PMZ) was smaller. The tensile strength and the elongation of the welding joint were 274 MPa and 12.42%, which is approximately 85.63 and 95% of that of base metal, respectively.

An investigation on plasma-MIG hybrid welding of 5083 aluminum alloy

Investigation of the stress corrosion cracking behavior in annealed 5083 aluminum alloy sheets with different texture types

Preparation of multifunctional Al-Mg alloy surface with hierarchical micro/nanostructures by selective chemical etching processes

Structural aluminum alloys are used in marine applications where light weight and increased speed are paramount. The 5xxx series alloys are the ideal choice, providing an optimum combination of as-welded strength and general corrosion resistance. A particular concern is sensitization in service. Aluminum is considered sensitized when a nearly continuous network of β phase forms along the grain boundaries. The β phase is anodic to the Al matrix, and, when exposed to sea water and sufficient loading, provides a clear pathway to stress corrosion cracking (SCC). The degree of β-phase precipitation is driven by a combination of time and elevated temperature. For over a decade, SCC of Al superstructures has plagued Navy ships. To address this issue, relevant technologies have been adopted, adapted, and developed to combat this issue. More specifically, the technology areas involve the detection of sensitization, the mitigation of SCC, and the replacement of corrupt materials. The technologies discussed herein a...

Survey of Detection, Mitigation, and Repair Technologies to Address Problems Caused by Sensitization of Al-Mg Alloys on Navy Ships

Between November 2006 and March 2009, the US Navy's first Zumwalt class guided missile destroyer, DDG 1000, underwent detailed design. According to a Government Accountability Office shipbuilding study in 2005, late changes to a ship's design is recognized as the primary factor contributing to increasing ship construction costs. Therefore, a strict detailed design review process was implemented for DDG 1000 that included improved computer-aided design tools and more efficient communication methods than previous ship detailed design efforts. The actual benefit of the design reviews of the ZUMWALT class will not truly be known until after the lead ship has been commissioned; however, the design reviews, along with the unprecedented involvement by stakeholders via an integrated data environment, have already proved to be an effective means for reducing the probability that setbacks will be encountered at the waterfront.

G. R. Grogan

Papers

Survey of Detection, Mitigation, and Repair Technologies to Address Problems Caused by Sensitization of Al-Mg Alloys on Navy Ships

Performing Detailed Design Reviews of a US Navy Surface Combatant within an Integrated Data Environment