Mixed Titanium Alloys in Seawater

[DNJ]

Does anyone have experience in putting commercially pure titanium (grade 2, ASTM B348) in direct contact with 6Al4V titanium (grade 5, ASTM B348) in seawater. Seawater temperature is between 5 and 10 deg. C. Surface areas of the two components is approximately equal. I am concerned that I might form a galvanic couple that will cause one of the components to corrode.

 

[rnd2]

The electrical potential difference would be minimal and given the rapid forming insulative properties of the oxide, reasonable to expect little to no galvanic corrosion to occur provided the sea water is well oxygenated.
Can you electrically isolate the parts?
What is the manufacturer's recommendation?

 

[DNJ]

Thanks rnd2:

Since posting this thread I did a Dialog search and found a paper by some Chinese materials engineers on this specific topic. ("Study of Galvanic Corrosion of Titanium Alloys in Seawater" by Zhu, Xiangrong; et. al. published in Memoires et Etudes Scientifique de la Revue de Metallurgie). They report no galvanic corrosion occurs with various Ti alloys in contact in seawater. I also found that Ti can be put in contact with more noble materials in seawater, and titanium's oxide film will be "reinforced" by the driving potential of the more noble alloy, thus raising its potential to meet that of the more noble alloy. See

http://www.key-to-metals.com/Article24.htm.

Based on these reports, I feel little risk in putting grade 5 Ti in contact with Grade 2 and do not think there is a need to electrically isolate them.

Thanks for your comments.

Regards, DNJ