White paper about the global need of knowing more about corrosion

Take a few minutes of your day and read this white paper about corrosion - not only corrosion on aluminum.

Extract from the foreword of the white paper.

The science of corrosion prevention and control is highly complex, exacerbated by the fact that corrosion takes many different forms and is affected by numerous outside factors. Corrosion professionals must understand the effects of environmental conditions such as soil resistivity, humidity, and exposure to salt water on various types of materials; the type of product to be processed, handled, or transported; required lifetime of the structure or component; proximity to corrosion-causing phenomena such as stray current from rail systems; appropriate mitigation methods; and other considerations before determining the specific corrosion problem and specifying an effective solution.

One of the figures shows severe pitting corrosion on aluminum and how temperature and aluminum alloy influence on the corrosion attack.

If you have a corrosion problem you need to solve on aluminum, I have the solution and you can get started immediately for the price of $495.

Interested send me an email adj@aluconsult.com

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Aluminium 2000 congress in Bologna, Italy

Last week the 7th Aluminium Two Thousand International Congress took place in Bologna, Italy. Around 350 people attended from 25 different countries.

With the motto "Let´s build the future of the aluminum world together" the days were fully packed with experts from all around the world. The three day program with parallel sessions included analysis of the aluminum industry, interesting new developments within all different aspects of the aluminum industry; foundry, casting, extrusion, anodizing and painting, automation, architecture, transport industry, environmental protection and recycling, measuring, testing and quality techniques.

A lot of the presentations were about how to save money, which is probably understandable because this is a topic we all can relate to and want to hear more about.

So I was very honored to be asked to present a paper on the cost savings when changing from conventional DC anodizing to Pulse anodizing.

The paper and presentation showed that the ROI is less than a year for an Anodizing line to switch from conventional DC to Pulse anodizing - all because of the increase in productivity.

I am proud to say that the paper, among three others, was awarded "Most interesting presentation", at the congress.

Purchase my paper presented at the 7th Aluminium Two Thousand Congress

If you find this article useful and you would like to know more please contact me blog@aluconsult.com __________________________________________________

Coefficient of Friction between Anodized Aluminum and Steel

First a short introduction to friction and the friction coefficient.

Friction is the force resisting when two parts are moved against each other. This can be between solid surfaces, fluid layers and/or material elements. The subject here is between two solid surfaces, also called dry sliding friction, no fluid in the sliding area.

The coefficient of friction is defined by the applied load between two parts, L, and the resultant friction force required to slide the two parts, F.

The Coefficient of Friction, µ, is given by

µ=F/L (the value is dimensionless).

The dry sliding friction coefficients vary a lot depending on the surfaces characteristic of the two parts. It is important to mentioned here that all friction coefficient values should be treated with caution because the value is very dependable of the environment and operating conditions.

The following table is taken from SIS Handbook, Aluminium, ed. 3, June 2003 and edited by me. The aluminum alloy used is not mentioned.

	Against steel	Against its self
Hard anodizing	0,22	0,17
Anodizing	0,30
Hard anodizing with Teflon	0,14	0,11
Aluminum	0,61*

* from Wikipedia

The value of the friction coefficient has to be dependent on the uniformity and quality of the anodic layer formed. So therefore the value would be dependent of the aluminum alloy used because of the difference in quality of the anodic layer.

For any specific application the ideal method of determining the coefficient of friction is by trials.

As mentioned above sometimes there is a fluid layer involved which will immediately change the picture. This figure is taken from The English Surface Finishing Company, Poeton.

If you find this article useful and you would like to know more please contact me blog@aluconsult.com __________________________________________________

Happy New Year

Dear Anodizing World readers

2011 is already rolling with the possibility of new ideas, new goals and new questions.

With a hope of a prosperous 2011 I look forward to write a lot of interesting posts about aluminium and anodizing this year.

This year will also be the year where my first Ebook about anodizing will be launched, so stay tuned.

You will find the first two anodizing news in this New Years post.

As a board member of the Aluminum Anodizers Council and Vice chairman of the Education committee I am happy to announce the first poster session for students ever with only focus on anodizing. The poster session will take place at the 20th Annual Anodizing Conference in Phoenix, AZ in October.

Take a look at the Aluminum Anodizers Website if you are interested, or know a University or a student who works in the area of anodizing.

If you are an anodizing freak like me, you will love this animation of the hard anodizing process. Take a look at Luke Engineering and Manufacturing Co., Mr. Chris Jurey is the retired President of the International Hard Anodizing Association and the one who made 2010 symposium fantastic and with very interesting papers.

If you would like to know more please contact me at blog@aluconsult.com

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A question about corrosion of aluminum in contact with stainless steel

I always appreciate when my readers contact me for more in-depth information regarding a specific issue. This time the question was regarding galvanic corrosion between aluminum and stainless steel.

The earlier post the question came from is the post, Corrosion between anodized aluminum and steel.

The question was:

I´m still a bit confused on the effect anodizing has to this corrosion problem. You stated that it can be superior choice but also make it worse. How will I know?

Below you will find my answer:

Aluminum is a reactive (un-noble) metal compared to most of the metals used. Aluminum will therefore almost always be the anode, the part which corrodes, in contact with other metals, but because of the natural formed oxide layer Aluminum can be a called a passive metal. So Aluminum behaves as a very stable metal, especially in oxidizing media such as air, water, etc.. This natural formed oxide layer differs in density compare to the underlying aluminum, which makes the aluminum oxide less likely to crack when deformed. The dissolution rate of aluminum oxide depends on the pH value, see figure below.

The corrosion rate (dissolution rate of the aluminum oxide) is not solely dependent on the pH but also what kind of acid or alkaline solution we are talking about. Sodium hydroxide at 0.1 g/l is 25 times higher than in an ammonia solution at 500 g/l. For the acids solutions of hydrochloric acid or hydrofluoric acid are much more aggressive than solutions of acetic acid. It is though very important to recognize the different slopes of the curve depending on which side on the pH scale the aluminum is exposed too. High pH has much higher corrosion rate than for a low pH.

So what I am saying is, take a careful look at your environment, if you are out of the pH range 4.5 - 8.5 you should immediately be aware of a possible corrosion issue. This is the same whether you have an anodized surface or not. The protective oxide film will not be protective anymore, leaving a part smaller or bigger part of the aluminum unprotected.

If a very small area of the protective film has been destroyed, exposing a small anode area, as shown it the picture in the post, due to cracks or a scratch or something else then you will know that you have a corrosion problem.

This will lead to a small anodic area (un-protective aluminum) relative to the cathode area (the stainless steel) and this should be avoided. The larger the relative anode area, the lower the galvanic current density on the anode, the lesser the attack.

A practical illustration of what I am saying is on anodized aluminum frames in windows, especially in salty environments. Some have stainless steel clips riveted to them destroying the anodic oxide film, in other places there are normal carbon steel bolts through the frames with no destruction. There is zero evidence of corrosion between the steel bolts and the anodized aluminum frame. In the areas of the rivets the anodized aluminum frame is completely and totally eaten away underneath the stainless steel clips. Outside this region there is no corrosion.

If you have a specific problem, I would happy to help you as a consultant . Take a look at one of my products and let me know if you would be interested.

Troubleshooting Aluminum surface issues!

Send me your surface finishing issue per. email, preferably with a photo, then I will ask detailed questions which you answer before the call, during the call we will clear out your questions together, coming up with ideas, new opportunities and results. After this call if you have any follow-up questions about the topic, you can sent an email, which I answer within in 48 hours.

Your investment?

An e-mail and one hour, and $495. Money you've earned into multiples when you can reduce your time used on this specific issue, and know what to expect of your product and what your requirements are.

Payment is easily done by PayPal using any major credit card, or to my Wells Fargo Account.

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Hardness versus Wear resistance

The first post about the hardness of the aluminum oxide formed by the hard anodizing process described the various types of hardness test, Vickers, Knoops, Brinell and Rockwell.

This second one will give an idea of the differences between the hardness of the hard anodized coating (hard anodizing) and the wear resistance of the hard anodize anodic process. This text will also have referrals to presentations at the International Hardanodizing Association´s symposium in September 2010 in Las Vegas.

Aluminum oxide is almost as hard as diamond (1200 HV or more) but in general too thin to increase the hardness of the aluminum metal itself. It will not protect against strong pressure but it will resist surface scratches and therefore protect the overall appearance of the surface.

The hardness of the aluminum oxide layer formed by anodizing, increases by decrease in temperature of the electrolyte and in the acid concentration. The hardness is also increased by an increase in the homogeneity of the microstructure and by an increase in the current density used to form the aluminum oxide film.

Prof. Allan Matthews of the University of Sheffield, England pointed out in a presentation that "Wear = constant load/hardness is a commonly accepted relationship. However this equation is nonsense, because it ignores the many different types of wear, such as impact, fretting, abrasion, friction sliding and others."

In fact, the Elastic modulus is also very influential, and the ratio of hardness (H) to modulus (E) gives a better indication of wear resistance than either alone.

If the hardness is too high, the coating is susceptible to cracking. However, ductility allows a coating to accommodate deformation. When the ration H/E is high, then wear resistance is good.

Mr. Leonid Lerner from Sanford Process Corp., US showed in his presentation at the IHAA symposium a great slide of the two different directions which we expose the oxide layer for external stresses depending on if we test or use it in normal applications.

When testing the aluminum oxide film formed by the hard anodizing process it is normally done on a cross, shown in Image A and is explained more in the first post about how to define the hardness of aluminum oxide formed by hard anodizing.

This leads to a stress horizontal and perpendicular to the hexagonal oxide cell structure (Cross-sectional View, see right bottom of the slide).

Whereas the mechanical stresses in normal applications will be vertical and perpendicular to the hexagonal oxide cell structure (Top View, see left bottom of the slide).

So even though the hardness of the aluminum oxide film itself is very hard, it is way to thin to increase the hardness of the aluminum metal itself.

The hardness of the aluminum material is most often proportional to the abrasive wear resistanc but as explained above,the hardness of the aluminum oxide film formed by hard anodizing will not always be proportional to abrasive wear resistance.

Maximum abrasion resistance of the aluminum oxide is found on pure aluminum and aluminum-magnesium alloys for the same hard anodizing process parameters.

Sealing decreases the wear resistance of oxide film formed by hard anodizing up to 50 - 70 % of the unsealed value.

If you find this article useful and you would like to know please contact me at blog@aluconsult.com__________________________________________________

Summery of two important anodizing conferences

This year two anodizing conferences took place in a row.

The International Hard Anodizing Association, IHAA, 13th Technical Symposium in Las Vegas,NV September 29 - October 1, 2010 and the Aluminum Anodizers Councils, AAC, 19th AnnualInternational Anodizing Conference & Exposition, October 5-7, 2010 in Montréal, Québec, CA.

The International Hard Anodizing Association symposium

72 hard coat people from all over the world listened to the most experienced and knowledgeable industry and university experts, talking about all different topics regarding hard anodizing. Topics as plasma electrolytic oxidation, advanced anodizing using process control technology, Interfacial Phenomena, Hard Anodizing 7000 alloys, blistering, flaking and pitting, hardanodizing - what is hard?, Hardness vs. Wear resistance, Oxalic Acid Anodizing in Japan, FDAapproval of Hard Anodizing, Dyeing Anodic Coatings and much more - plus the very importantpart of this symposium - the networking between the sessions and during the lunches and dinners.

The Aluminum Anodizers Councils Conference

Some of the people who attended the IHAA symposium chose to fly up to Canada to meet with140 people from the anodizing industry. General sessions and three different focus sessions gave a lot of opportunities to hear what ever you thought interesting, and meet a lot of different people.

If you find this article useful and you would like to know more please contact me blog@aluconsult.com __________________________________________________