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Assumed we have a fuel flask that is made of titanium. The bottle will be filled with white gasoline when used. At the bottleneck there is a standardized thread manufactured into the titanium.

Are there any dangers of (contact-)corrosion between the materials if the screwed-in bottle cap is made of aluminium instead of titanium?

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Galvanic Compatibility

Often when design requires that dissimilar metals come in contact, the galvanic compatibility is managed by finishes and plating. The finishing and plating selected facilitate the dissimilar materials being in contact and protect the base materials from corrosion.

For harsh environments, such as outdoors, high humidity, and salt environments fall into this category. Typically there should be not more than 0.15 V difference in the "Anodic Index". For example; gold - silver would have a difference of 0.15V being acceptable.

For normal environments, such as storage in warehouses or non-temperature and humidity controlled environments. Typically there should not be more than 0.25 V difference in the "Anodic Index". For controlled environments, such that are temperature and humidity controlled, 0.50 V can be tolerated. Caution should be maintained when deciding for this application as humidity and temperature do vary from regions.

Anodic Index

Metallurgy Index (Volt)

Nickel, solid or plated, titanium and alloys & Monel (0.30)

Aluminum, wrought alloys of the 2000 Series (0.75)

Aluminum, wrought alloys other than 2000 Series aluminum, cast alloys of the silicon type (0.90)

Aluminum, cast alloys other than silicon type, cadmium, plated and chromate (0.95)

https://www.corrosion-doctors.org/Definitions/galvanic-series.htm

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  • $\begingroup$ I guess corrosion will only appear if the parts are connected together for several years, no? After a few weeks of contact nothing will happen I guess, even in rough conditions? $\endgroup$
    – Dave
    Dec 15 '21 at 22:29
  • $\begingroup$ Galvanic action occurs right after the contact. Depending on the environmental/exposure factors, the effect (corrosion) can take a while (months, years) to be noticeable. $\endgroup$
    – r13
    Dec 15 '21 at 23:18
  • $\begingroup$ I actually thought that, to cause galvanic action, it is always mandatory to have some liquid electrolyte between the two materials, no? So in dry conditions or alternative with some non-polar solvent in between, nothing should happen at all? $\endgroup$
    – Dave
    Dec 17 '21 at 8:10
  • $\begingroup$ You are correct, it needs electrolytes to get started. $\endgroup$
    – r13
    Dec 17 '21 at 14:21

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