ssc-452 aluminum structure design and fabrication guide ship

Aluminum Marine Structure Guide
Unrecrystallized
Recrystallized
Figure 2- 5 Grain structure of 5xxx-series aluminum (Courtesy of Alcoa).
To address the problem of intergranular corrosion, the American Society of Testing and
Materials (ASTM) formed the ASTM B07.03 Task Group on Marine Alloys, and The Aluminum
Association formed a similar group. The task group developed a new specification for marine
aluminum alloys, ASTM B 928-04, High Magnesium Aluminum-Alloy Sheet & Plate for Marine
Service. This specification replaces specification ASTM B 209 for all high magnesium (≥ 3%)
alloys and tempers intended specifically for marine application service. Specification B 928-04
includes the ASTM G 67 (NAMLT) test to determine an alloy's susceptibility to intergranular
corrosion in addition to the ASTM G66 (ASSET) test to determine susceptibility to exfoliation
corrosion. The new ASTM standard and the Aluminum Association have reserved the H116 and
H321 tempers for wrought products in the 5xxx-series having a nominal magnesium content of 3
percent or greater. In addition, the definitions of both the H116 and H321 tempers have been
modified to require testing for both inter-granular and exfoliation corrosion resistance.
Previously the H116 temper required only exfoliation corrosion testing, and the H321 temper had
no defined requirement for corrosion testing.
The new definitions have been approved by American National Standards Committee
H35 and are published in ANSI H35.1 / H35.1(M)-2006. The task group has brought about
similar changes to document W25 of the International Association of Classification Societies, the
organization by which classification societies such as ABS establish common standards. The
task group is also working to eliminate the relevant subsections of the U.S. government material
standard for aluminum sheet and plate, QQ-A-250 to avoid conflicts with the new ASTM
specifications (Skillingberg, 2006).
The new definitions in ANSI H35.1 / H35.1(M)-2006 are as follows:
“H116 - Applies to products manufactured from alloys in the 5xxx series, for which the
magnesium content is 3% nominal or more. Products are strain hardened at the last operation to
specified stable tensile property limits and meet specified levels of corrosion resistance in
accelerated type corrosion tests. They are suitable for continuous service at temperatures no
greater than 150°F (66°C). Corrosion tests include inter-granular and exfoliation;”
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