Alclad Question

[Rick6a]

We all know an alclad surface is naturally corrosion resistant. To some of us that can mean "no primer required". My question pertains to those kit parts that do not have the (usually blue) vinyl coating on them to protect their alclad surfaces from scratches etc. Specifically, my question pertains to wing ribs which we must straighten and flute. It is my understanding these parts after being stamped out in a press, are heat treated. True? If so, do these parts still possess a 100% pure alclad coating?

[airguy]

Heat treating will only remove/damage the alclad if the temperatures used are high enough to melt the pure aluminum cladding. The melting point differential between the cladding and the aluminum alloy used for the main part is relatively small, so heat treating will stay well below these temperatures. Heat treating will not damage the alclad.

[TerryWighs]

Rick...I am a bit confused about something. I was not aware that the ribs in the kit were in fact alclad ?

[Sam Buchanan]

I was not aware that the ribs in the kit were in fact alclad

Ribs and bulkheads are indeed Alclad, their dull finish is due to the forming process. I am not aware of any heat treating of any of the sheet stock.

[frankh]

Primer wars is a wonderful conflict to behold but the I believe its a lot of hot air.

For example Vans would have you believe that you HAVE to completly cover 6061T6 or it will corrode.

That is nonsence as there are a few homebuilt designs (the zenair Zodiac for example) that are completly constructed of 6061 and only have a coat of primer between the mating surfaces...The rest is bare.

Didn't have a hit of corrosion in 7 years...If I lived on the coast I might cover all the internal surfaces but other wise I just did the same as on my Zodiac.

Frank

[Mel]

Murphy aircraft kits are also completely 6061 aluminum. 6061 alloy is actually quite corrosion resistant. Many Murphy and Zenair aircraft have been flying for years with no primer inside or out with no problems.

[Captain Avgas]

Originally Posted by Rick6a

We all know an alclad surface is naturally corrosion resistant. To some of us that can mean "no primer required". My question pertains to those kit parts that do not have the (usually blue) vinyl coating on them to protect their alclad surfaces from scratches etc. Specifically, my question pertains to wing ribs which we must straighten and flute. It is my understanding these parts after being stamped out in a press, are heat treated. True? If so, do these parts still possess a 100% pure alclad coating?

All Vans structural sections (angles, bar, channel etc) are extruded from alloy 6061 and heat treated to temper T6. They have no Alclad. All the sheet and the components formed from sheet (skins, bulkheads, ribs etc) are alloy 2024 heated treated to temper T3. They all have Alclad. There is no further heat treating of any components after forming. Despite what a number of people may say aluminium, even with Alclad, oxidises quite readily and untreated it performs very poorly in a saltspray test.

In respect of the priming war. It's really simple actually. Proper milspec two pack priming (as now done by Cessna, Piper and every other reputable certificated manufacturer) is messy, requires research to apply, is possibly carcinogenic, is expensive, takes a lot of time...and is definitely NOT fun.

What then compells builders to go down that path. In a word...quality. Some people are just innately compelled to pursue excellence.

For the rest there's the rattle can...or nothing at all.

But the amazing thing is that in all the years I've spent reading the endless primer war threads I've never yet come across a single builder who admitted he didn't prime because he simply couldn't be stuffed. No nary a one. Without exception they all proclaimed that they didn't prime because there is no NEED to prime. It's funny about that.

[Rick6a]

Originally Posted by Captain Avgas

. In a word...quality. Some people are just innately compelled to pursue excellence.
But the amazing thing is that in all the years I've spent reading the endless primer war threads I've never yet come across a single builder who admitted he didn't prime because he simply couldn't be stuffed. No nary a one. Without exception they all proclaimed that they didn't prime because there is no NEED to prime. It's funny about that.

When I built my 6A, I prepped and Akzo epoxied primed virtually everything, even the contact surfaces on the nutplates. Such was the lasting impression of all the years I spent at McDonnell-Douglas. HOWEVER, on the completely opposite end of the spectrum, my 40 year old and virtually primer free 1966 C-150 just underwent a prebuy inspection and the IA remarked at how little corrosion he found.
As I build the 8, a major goal this time around is building in lightness not just in words but in deeds. My 6A is not particularily heavy at 1096 lbs. but I know I can do better. That means carefully and thoughtfully reviewing every builder decision. At 59 years old, priorities change. I figure as long as the plane lasts 20-30 years, I'll be happy. This time around, I intend to prime only certain and key areas. Of course a lot of this decision is based upon living in the Midwest! If I lived in Hawaii, I might very well hold to a different position. In the end, arguing about primer is a little like arguing about politics. No matter which position you take, your views will resonate with some, alienate some, and the rest will continue to have no opinion.

[Captain Avgas]

Originally Posted by Rick6a

This time around, I intend to prime only certain and key areas. Of course a lot of this decision is based upon living in the Midwest! If I lived in Hawaii, I might very well hold to a different position.

People live in the midwest but because of the speed and range of an RV they invariably fly to coastal locations (but probably not in a Cessna 150).

That's the thing...it's not necessarily where builders live that matters...it could be where they travel to. Once the salt gets between the interfaces it's almost impossible to get it out. And everytime there's further condensation or moisture the salt just reactivates.

I trust you're not planning on a holiday in the Caribbean.

Incidentally, the best treatment between disimilar metals (such as Cadmium plated nut plates and aluminium) is not primer but a barium chromate compound such as Duralac or similar. Electrolytic corrosion can be particularly nasty.