Surface Finishing on Aluminium

McDermid offer Iridite NCP (non chrome passivate)

http://www.macdermid.com/industrial/aluminum

Thanks, but this gives less than 24 hours before corrosion on a standard salt spray test! Our problem is aluminium 2024 fastening onto stainless steel. OK on 6061 it is good...over 1000 hours.

Have you considered electroless nickel?

What about Anodized Aluminum?

http://www.wisegeek.com/what-is-anodized-aluminum.htm

I may be wrong but I don't believe that anodize is as resistant to salt spray as nickel. The acids used in the anodize process may react with the salt. Anodize is done with sulphuric and oxalic acids. When you machine an anodized aluminum part you can smell the acid, so I would think that there may be a reaction. If someone has more info, please correct me on this.

Hi,

I am shure there is an anodizing process suited for the 6xxx alloys, may be no for the 2xxx.

The sealing of the pores that is necessary to get good corrosion properties prevents any attack to the beneath aluminum.

I have seen a lot of outside applications in corrosive industrial atmosphere (containing H2SO3 and H2SO4 derived from abundant SO2 reacting with water with and without some further oxidation).

These panel structures used on buildings have a typical brown color from the oxalic acid anodising process.

Ask some local supplier, but be cautious, there are many different processes existing.

RHABE

www.ieeexplore.ieee.org/Xplore/login.jsp?url=/iel3/3932/11381/00533484/pdf?tp=&isnumber=11381&arnumber=533484

Corrosion properties of the samples and the components were evaluated using both a 500 hour salt spray field test and a laboratory electrochemical corrosion system. The tested samples were then analyzed by scanning electron microscopy. Corrosion measurements have demonstrated that PSII can significantly improve the pitting resistance of 6061 aluminum. By correlating the analytical results with the corrosion test results, it has been verified that the improved corrosion resistance in PSII-treated coupons is due to the formation of a continuous AlN layer. It was also identified that the formation of a continuous AlN layer

A bit exotic for us. We need to coat millions of aluminium fasteners used by very "commercial" not aerospace users, so it has to be dip spin or similar with a low temperature bake

For Europe it is the product Metfin NC3551 of the mfg. Orapi-Applied. Aluminium 1000 hrs. Is has a Qualicoat certificatie, that's all I know.

What about Xylan?

http://www.whitfordww.com/design/solvingprobs.html

I am sure we have looked at Xylan. We use Deltaseal GZ, but the bake temperature is such that unless it is kept low (40-60degrees) the 6061 alloy goes erratic! And the platers cannot control the baking temperature reliably for a variety of reasons!

You've selected 6061 for reasons unknown maybe availability and price but possibly a 2400 series would accommodate the restrictions of your protective coating process. Free machining is a characteristic of 2400 series also, I always preferred its tensile properties.

We cold forge from wire a pin in 2024 and a collar in6061. These alloys are not possible to change! No wasteful machining!

www.ieeexplore.ieee.org/Xplore/login.jsp?url=/iel3/3932/11381/00533484/pdf?tp=&isnumber=11381&arnumber=533484

Please examine the findings of this example of treating 6061 threaded fasteners with a protection for use in a corrosive saltwater environment.

Well there are always zinc phosphate conversion coatings like alodine or iridite, but they won't protect all that well. I'd say that anodizing is probably your best choice. If acids are your corrosion issue you should not be using aluminum anyway. Aluminum is terrible in acidic environments. But it is fine for salt spray environments. We used to use type 3 anodized aluminum 6061-t6 for hydraulic manifolds on subsea ROV's when I worked at Sonsub and we had no problem.

Thanks, the problem we have with anodising is that we have to do relatively small 2024 parts (1/4 inch dia by 2inch long with a 1/2inch dia head) in large volumes (50000) lots and so cannot wire them up, they have to be Barreled and you get unanodised "spots" where parts tumble together! Not too bad in silver, but it does show up. I understood Alodine has Chrome 6? The environment is on road vehicles holding stainless steel buckles on to webbing and the alum fastener is plenty strong enough, the cutomers won't pay for stainless and steel fasteners go red and streaky! We have tried Delta GZ, but control of the temperature in baking is the problem with 2024, the 6061 component is fine! We will get there, there has to be a way!

I'm just thinking out loud, but what about brass or zinc plated steel? or conventional zinc based primer paint? Lots of companies do large batches of anodized (cosmetic) parts, surely there has got to be a way to rack them to minimize spotting.

Not when we are looking at a price similar to commercial plating - Deltaseal GZ $1.50 kg! and it almost works

I remember using a reactant on AL when contact saltwater the surface oxidized in a manner preventing or slowing further corrosion significantly. Pity I don't recall the component used.

I've just found this. Looks interesting: Alodine^® EC^2™ ElectroCeramic Coating delivers benefits throughout the entire coating process and over the life of your coated products. When protection is essential from the forces of nature or the forces of man, Alodine^® EC^2™ withstands the most extreme conditions, prolonging the ability of your aluminum, titanium and light metal components to perform at optimum levels.

www.henkelec2.com

---best,czes

Thanks, looks interesting if there is someone licenced to do it in the UK! I will investigate!!

D

If you're in UK you may follow this technology:

DURNI-COAT^® is a process for the functional coating of ferrous and non-ferrous materials.

The DURNI-COAT^® process consists in electroless deposition without any external source of electricity. In this process the workpiece is immersed into an aqueous process solution with a specific content of nickel ions. During the process these ions are reduced into metallic nickel. The chemical reacting agents and formulators of the electrons required in this process are the hypophosphite ions in the solution. These agents are transformed, by oxidation in the course of the reaction, into orthophosphite. A nickel-phosphorus alloy layer forms on the workpiece's surface. This layer effectively protects the workpiece against wear and corrosion.

http://www.aimt-group.com/200-1-basics.php

---best,czes