Stainless Steel DZUS in Aluminium - problems to be expected?

[chrisB]

Hi everybody,

we have a lot of old DZUS fasteners in our T-6G cowlings and co. (mainly F6 1/2-45, F5-35 and FJ 5-40), partially worn out or with signs of corrosion.

The idea is to replace them with stainless Steel DZUS and leave them unpainted. I found Rich´s pics about DZUS Removal and got one of these rotabroach hole-saws....but I won´t start to remove the old ones unless I have the new ones

Are there any problems to be expected using SS DZUS in aluminium holes? Contact corrosion?

Is DFCIS the only manufacturer that produces new ones?

Thanks for your help.

Chris

[51fixer]

Hi everybody,

we have a lot of old DZUS fasteners in our T-6G cowlings and co. (mainly F6 1/2-45, F5-35 and FJ 5-40), partially worn out or with signs of corrosion.

The idea is to replace them with stainless Steel DZUS and leave them unpainted. I found Rich´s pics about DZUS Removal and got one of these rotabroach hole-saws....but I won´t start to remove the old ones unless I have the new ones

Are there any problems to be expected using SS DZUS in aluminium holes? Contact corrosion?

Is DFCIS the only manufacturer that produces new ones?

Thanks for your help.

Chris

SS shouldn't be a problem except for expense. Standard ones properly plated with electro less nickel look good too.

[snj-5]

Stainless Steel and Aluminum are kind of on the opposite ends of the galvanic scale, but properly cared for (hangared, etc.) it would likely take decades for any issues to manifest themselves.

Cad (and Nickle) plated steel is actually closer to Aluminum on the galvanic scale, and, provided the plating stays intact,
would be more compatible with Aluminum over time.

Bela P. Havasreti

[bdk]

Lots of folks sell stainless hardware kits for Bonanzas. Not a good galvanic match for the beach, but shouldn't be a problem if well cared for.

Is the stainless steel replacement approved for your application? Would you replace the carbon steel wing attach bolts with stainless steel too?

[chrisB]

@ all: once again, thank you for the quick response/inputs
@ bdk: yes, it is approved / for the moment no plans exist to exchange the wing attach bolts to stainless steel too

[skymstr02]

Is the stainless steel replacement approved for your application? Would you replace the carbon steel wing attach bolts with stainless steel too?

Difference between structural and non-structural. Exchanging fairing and non-structural hardware is a minor alteration, but when you get to structural hardware, the stainless bolts have a lower shear strength than AN/MS/NAS carbon steel variety, so that is not a good idea.

Same thing with the screws that attache the stress plates over the fuel tanks, they are structural attach hardware.

The stainless Dzus fasteners and the galvanic issues should not be a problem due to the aluminum grommets that retain them in the panels, the stainless doesn't come into contact with the panel itself.

[51fixer]

The dissimilar issues can be greatly reduced involving SS by a chemical procedure call Passivating. It forms an oxide barrier on the SS part. This also helps any paint to adhere to the SS surface.
Many years ago while stripping the paint off of the POF SBD cowling the SS on the top which protected the Alum from weapons use had the term Passivated etched in it.

Skin panels with Dzus fasteners should trap or hold little moisture as it will drain or evaporate quickly. I see more rust on the Springs than corrosion on any adjacent skin. I would be wary of SS hardware in the wing attach angles. The angles and the plate will collect moisture, organics, chemicals and fluids like oil, fuel and hyd. zI would see that area having draining issues and more potential for alum corrosion due to dissimilar metals. Some hardware removed for Insp of the angles has been rusted in the past.

Also the T-6 series use SS for cowl formers, the dishpan around the exhaust and the rear individual dzus mounts are all SS and I've seen very little corrosion in any of those cowl panels.

[The Inspector]

The dissimilar issues can be greatly reduced involving SS by a chemical procedure call Passivating. It forms an oxide barrier on the SS part. This also helps any paint to adhere to the SS surface.
Many years ago while stripping the paint off of the POF SBD cowling the SS on the top which protected the Alum from weapons use had the term Passivated etched in it.

Skin panels with Dzus fasteners should trap or hold little moisture as it will drain or evaporate quickly. I see more rust on the Springs than corrosion on any adjacent skin. I would be wary of SS hardware in the wing attach angles. The angles and the plate will collect moisture, organics, chemicals and fluids like oil, fuel and hyd. zI would see that area having draining issues and more potential for alum corrosion due to dissimilar metals. Some hardware removed for Insp of the angles has been rusted in the past.

Also the T-6 series use SS for cowl formers, the dishpan around the exhaust and the rear individual dzus mounts are all SS and I've seen very little corrosion in any of those cowl panels.

Try to stick to the same nobility with metals. Years ago Boeing pretty much didn't care what screw took which washer or nut in small assemblies and especially grounds. Come first 'C' check for an airplane and the phones were ringing of the hook from Narrow Seat Airways to Boeings warranty department and engineering because of serious galvanic corrosion caused by the dissimular metals were miniature batteries and reacted with each other and were literally eating airplanes alive.

CRES is far too soft for major structural attachments and attach fasteners it stretches and tears. Trim, rub strips, exhaust stream deflectors, doublers, and exposed light load attachment or pivot brackets should be about the limits and if you are going to place CRES directly onto Aluminum I strongly recommend a very stout layer of weather proof fay seal and edge sealing after installation using Ti fasteners which are not reactive.

[51fixer]

The dissimilar issues can be greatly reduced involving SS by a chemical procedure call Passivating. It forms an oxide barrier on the SS part. This also helps any paint to adhere to the SS surface.
Many years ago while stripping the paint off of the POF SBD cowling the SS on the top which protected the Alum from weapons use had the term Passivated etched in it.

Skin panels with Dzus fasteners should trap or hold little moisture as it will drain or evaporate quickly. I see more rust on the Springs than corrosion on any adjacent skin. I would be wary of SS hardware in the wing attach angles. The angles and the plate will collect moisture, organics, chemicals and fluids like oil, fuel and hyd. zI would see that area having draining issues and more potential for alum corrosion due to dissimilar metals. Some hardware removed for Insp of the angles has been rusted in the past.

Also the T-6 series use SS for cowl formers, the dishpan around the exhaust and the rear individual dzus mounts are all SS and I've seen very little corrosion in any of those cowl panels.

Try to stick to the same nobility with metals. Years ago Boeing pretty much didn't care what screw took which washer or nut in small assemblies and especially grounds. Come first 'C' check for an airplane and the phones were ringing of the hook from Narrow Seat Airways to Boeings warranty department and engineering because of serious galvanic corrosion caused by the dissimular metals were miniature batteries and reacted with each other and were literally eating airplanes alive.

CRES is far too soft for major structural attachments and attach fasteners it stretches and tears. Trim, rub strips, exhaust stream deflectors, doublers, and exposed light load attachment or pivot brackets should be about the limits and if you are going to place CRES directly onto Aluminum I strongly recommend a very stout layer of weather proof fay seal and edge sealing after installation using Ti fasteners which are not reactive.

For 15 years we have had SS Dzus installed on the P-51. No issues. For an eternity the T-6s have droned with Alum cowl panels attached to SS cowl formers. Also have used SS Timmerman or dimpled washers with SS screws to hold fillets on. All on an unpainted and polished A/C in the case of the P-51 fuselage and wing fairings.
None of these have provided any instances of corrosion in that time period.
Primarily these are 2024 Alclad Alum with some 5052 and 3003 thrown in.
In the last 35 yrs of working on warbirds these have not been issues needing attention.
But as far as structures and hardware keep it to specified metals/alloys/clading, specified hardware, use chemical and organic coatings and you'll have years of service.

[bdk]

Areas like this really show the difference between practicality and theory. The engineer in me says never do it, but the practical side of me says what is the risk- how much harm could it do?

As long as everyone is aware of the structural differences between carbon steel and SS hardware, it shouldn't be more of a problem than just money. SS fasteners may save a little time now in maintaining rusty screws in exchange for future galvanic corrosion risk on structural skin and non-structural fairings.