For our final project for Olin's Failure Analysis class, my team analyzed SCUBA tanks made from the AL6351 alloy, which
have been known to fail catastrophically in service due to sustained load cracking. Our team conducted microstructure analysis via multiple methods of destructive and
non-destructive testing, and determined overaging of the tank neck during the hot-forming process to be a major factor.
Axial CT scan showing crack
Radial CT scan showing crack
My contributions included:
- Optical and SEM Microscopy to analyze microstructure
- CNC machined dogbones from tank body
- Conducted Instron tension test on dogbones to determine mechanical properties
- Cut and prepared sections for microscopy
SEM micrograph showing inclusions and large grains
Optical micrograph of crack region
Our analysis concluded the hot press process used to form the tank neck overages the aluminum (as seen by the large grain sizes). Trace amounts of lead migrate
to the grain boundaries, causing solid metal embrittlement. This promotes crack propogation, which after years leads to catastrophic failure.
