Fasteners for aluminum to steel

[DougLoeffler]

We are having a fuel (gasoline) tank fabricated. We will need to use an existing sending unit. The housing of the sending unit seems to be made of grey iron or mild steel. A gasket will be used between the sending unit and the tank, but the sending unit must be attached to the tank with machine screws. The aluminum tank will have a series of threaded holes to receive the machine screws. The question is, if we can't avoid having the heads of the machine screws contact the sending unit, what material will be best for the machine screws? We could use aluminum, mild steel, SS, brass, maybe plastic, etc.
Thanks.

 

[CoryPad]

Will any part of the screws be exposed to an electrolyte, such as salt spray? Will the screw head be submerged in gasoline?





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[DougLoeffler]

No exposure to electrolyte, but the shaft of the screws will protrude slightly into the tank, or the tips of the screws will be at the inner surface of the tank, so they will probably get a regular dousing of gasoline as the gas sloshes in the tank.

 

[JimMetalsCeramics]

A possibility would be titanium alloy (e. g., T-6Al-4V) screws.

 

[CoryPad]

Doug,

If there is no electrolyte that connects the steel and aluminium parts, then you shouldn't have a disimilar metal corrosion problem. If there is not a large heat change, then you shouldn't have problems with thermal expansion/contraction. Therefore, use a steel screw since they are available in nearly all geometry configurations.


Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.