Anodizing World

White paper about the global need of knowing more about corrosion

noreply@blogger.com (Anne Deacon Juhl) — Thu, 16 Jun 2011 09:54:00 +0000

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

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

Aluminium 2000 congress in Bologna, Italy

noreply@blogger.com (Anne Deacon Juhl) — Fri, 27 May 2011 18:13:00 +0000

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

noreply@blogger.com (Anne Deacon Juhl) — Tue, 08 Feb 2011 11:55:00 +0000

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

noreply@blogger.com (Anne Deacon Juhl) — Fri, 07 Jan 2011 08:27:00 +0000

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

noreply@blogger.com (Anne Deacon Juhl) — Tue, 16 Nov 2010 19:05:00 +0000

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

noreply@blogger.com (Anne Deacon Juhl) — Thu, 28 Oct 2010 11:10:00 +0000

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

noreply@blogger.com (Anne Deacon Juhl) — Tue, 19 Oct 2010 17:30:00 +0000

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 __________________________________________________

Aluminium 2010

noreply@blogger.com (Anne Deacon Juhl) — Tue, 14 Sep 2010 07:27:00 +0000

8th World Trade Fair & conference in Essen has started. I am a part of the Danish Pavillion in Hall 5. This is three days with a lot of great aluminium talk and very interesting companies from all over the world.

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

Just Grand!

noreply@blogger.com (Anne Deacon Juhl) — Mon, 23 Aug 2010 18:48:00 +0000

Just Grand! is a very informative article from this months Product Finishing newsletter which gives a great view of the finishing market right now.

Read the article here

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

Great link to a lot of specifications

noreply@blogger.com (Anne Deacon Juhl) — Fri, 13 Aug 2010 10:10:00 +0000

Sometimes you need to find a special specification or an old one, this link is a great help then

http://www.everyspec.com/

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

Less than two months to the next Anodizing Workshop in San Diego

noreply@blogger.com (Anne Deacon Juhl) — Tue, 22 Jun 2010 19:49:00 +0000

Click here for registration

Register by July 14th and save $100

The anodizing workshop will be held at Holiday Inn Express San Diego Old Town

Make sure to let them know you will be attending the Surface Finishing Academy's Introduction to Anodizing Course to get the best possible rate.

Holiday Inn Express Old Town
3900 Old Town Avenue, San Diego – Old Town, CA 92110
Tel: 619-299-7400

If you want to know more about the anodizing workshop, please send me an email at blog@aluconsult.com __________________________________________________

How to define the hardness of the aluminum oxide film formed by hard anodizing

noreply@blogger.com (Anne Deacon Juhl) — Wed, 26 May 2010 21:05:00 +0000

The term “Hard Coat” or Hard Anodizing gives the impression of an anodizing process which gives a very hard anodic layer. The values below show that the anodic layer formed by this process really is harder but it is still important to remember that saying "Hard Coat" to an anodizer doesn’t give him enough information to process the metal.

HARDNESS COMPARISON between different materials

Untreated Aluminum Alloy 6082 - HV 100 - 120
Hard Anodized Alloy 6082 - HV 400 – 460
Stainless Steel - HV 300 – 350
Mild Steel - HV 200 - 220

The values are measured in (VPN) = Vickers pyramid number, also referred to as the Vickers hardness number (HV or VHN).

The Vickers hardness is the amount of force applied to the diamond divided by the area of the indentation the diamond makes in the material; in practice the diagonal of the pyramidal indentation is measured and the result is read from a table and is stated as an empirical measurement, without units.

Other hardness measurement numbers are found, such as, Brinell, Rockwell and Knoops. The Vickers hardness is up to about HV 500 about 1.04 times the Brinell hardness but most of the time hardness of the anodic oxide layer is measure by Vickers.

Knoops hardness is almost identical with Vickers hardness except for the form of the diamond. In this testing method the diamond has a rhombic-based pyramidal shape. The form of this

indentation makes it possible to measure the hardness of aluminum oxide more accurate but it is still not widely used.

The anodic oxide layer is very brittle and to obtain the best reproducibility of the measurements the Knoops diamond should be used. Using Vickers hardness measurements causes cracks in the oxide layer, so only measurements in the middle of the oxide layer are possible.

HARDENSS TESTING on anodic coatings should be carried out on the edge of the film so that the effect of the underlying, soft, aluminum is eliminated but not to close to the edge so the

softness of the resin influence the results.

The image to the right shows a cross section of a hard anodic coating with Vickers indentations and thickness measurements.

The pyramid has to be square formed to be sure of hardness value measured.

The light blue to the left is the aluminum alloy and the dark to the right in the picture is the resin.

THE MILITARY SPECIFICATION, MIL-A-8625F, for “Anodic Coatings for Aluminum and Aluminum Alloys” says nothing about any requirements of the hardness of Type III – Hard Anodic Coatings, see earlier post about this subject here.

The European Standard EN 12373 ”Aluminium and aluminium alloys – Anodizing” has none either. Both of them have on the other hand requirements of a wear resistance of the coating.

The maximum wear index for coatings on aluminum alloys having a copper content of 2 % or higher is of 3.5 mg/1000 cycles and 1.5 mg/1000 cycles for all other alloys.

Next post will discuss the wear resistance versus the hardness of hard anodic oxide coatings.

For more information on how to define your hard coat for your product please contact me blog@aluconsult.com

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Why is Hexavalent Chromium so hazardous

noreply@blogger.com (Anne Deacon Juhl) — Wed, 19 May 2010 19:40:00 +0000

The reason for the toxicity of hexavalent chromium is explained great on Wikipidia

Hexavalent chromium is transported into cells via the sulfate transport mechanisms, taking advantage of the similarity of sulfate and chromate with respect to their structure and charge.

Trivalent chromium, which is the more common variety of chromium compounds, is not transported into cells.

Inside the cell, Cr(VI) is reduced first to metastable pentavalent chromium (Cr(V)), then to trivalent chromium (Cr(III)). Trivalent chromium binds to proteins and creates haptens that trigger immune response. Once developed, chrome sensitivity can be persistent. In such cases, contact with chromate-dyed textiles or wearing of chromate-tanned leather shoes can cause or exacerbate contact dermatitis. Vitamin C and other reducing agents combine with chromate to give Cr(III) products inside the cell.

Hexavalent chromium compounds are genotoxic carcinogens. Chronic inhalation of hexavalent chromium compounds increases risk of lung cancer (lungs are especially vulnerable, followed by fine capillaries in kidneys and intestine). It appears that the mechanism of genotoxicity relies on pentavalent or trivalent chromium. According to some researchers, the damage is caused by hydroxyl radicals, produced during reoxidation of pentavalent chromium by hydrogen peroxide molecules present in the cell. Strontium chromate is the strongest carcinogen of the chromates used in industry. Soluble compounds, like chromic acid, are much weaker carcinogens.

Chromic acid is used in various surface treatments on aluminum, such as chrome plating, chromating and Chromic Acid Anodizing.

In the U.S., the OSHA PEL for airborne exposures to hexavalent chromium is 5 µg/m3 (0.005 mg/m3).

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Just finished my Anodizing Workshop in Chicago

noreply@blogger.com (Anne Deacon Juhl) — Wed, 12 May 2010 21:48:00 +0000

Two days of teaching, talking and networking.

Great to be together with people who love to talk about anodizing as much as I do.

If you missed this Anodizing Workshop, your next change will be in Wonderful Sunny San Diego, August 17 - 18 2010.

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Next Anodizing Workshop in Chicago

noreply@blogger.com (Anne Deacon Juhl) — Mon, 19 Apr 2010 09:53:00 +0000

Join us for the next Anodizing Workshop in Chicago from May 11 - 12, 2010.

If you simply just want to know more about anodizing, or why some parts are rejected and others not, or enjoy a great network opportunity with other people who love to talk about anodizing, then join us by clicking here.

Hear what one of the former attendees said about the Anodizing Workshop:

"I have attended Anne Deacon Juhl’s Anodize Workshop and would recommend it without any reservations. Her workshop is well structured and informative along with her excellent communication skills. Anne’s knowledge made the workshop interesting and enabled her to answer all of my questions to my satisfaction."

Rick Webster, Nelson Nameplate

Perhaps you want to build a new anodizing line, or just want to improve the old, see how a fully automatic line can look after working with me by taking a look to the right column where a short video shows the automatic anodizing line in Denmark.

If you are interested in knowing more about my products, please feel free to contact me or push the consulting button on top of the site.
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Happy news

noreply@blogger.com (Anne Deacon Juhl) — Tue, 13 Apr 2010 09:51:00 +0000

Finally it seems like the aluminum industry is improving after a couple of tough years. Alcoa´s CEO sees a positive trend in the aluminum use, read more.

At the same time I have been so fortunated to be appointed as external examiner at the Danish Engineering Universities, not only about anodizing but all kinds of chemistry and material engineering.

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Crevice Corrosion on aluminum

noreply@blogger.com (Anne Deacon Juhl) — Mon, 22 Mar 2010 19:33:00 +0000

This is the third post about corrosion on aluminum and it is about Crevice Corrosion. This type of corrosion is a localized corrosion in recesses, such as overlapping zones, bolting or welding, zones under joints, and under various deposits (sand, slag, precipitates, etc.) taken from Christian Vargel´s great book "Corrosion of Aluminium".

The localized corrosion may occur in the form of pits or etch patches. An important variable in crevice corrosion is the width of the crevice opening. The aluminum-silicon alloys corrode many times faster than the aluminium-magnesium alloy when crevice corrosion has started.

Prevention by

Applying corrosion inhibitor
Sealing crevices with an adhesive to prevent water penetration

Several reactions happen in the crevice. Aluminum is oxidized and on the edge of the crevice oxygen is reduced. The aluminum will corrode and the oxygen is dissolved in the liquid will be consumed. Due to the limited diffusion in the crevice the environment will be drained from oxygen and then leave the crevice with an excess of aluminum ions. This will lead to an inflow of chloride ions which will make the crevice acidic leading to a severe corrosion attack.

Corrosion costs are estimated at 4.2% of the Gross Domestic Product (GDP) or over $30 billion in the United States each year. Of this amount, 35% or over $100 billion can be classified as avoidable because best practices are not used.

If you need consulting with your corrosion issues please contact me blog@aluconsult.com
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How to decide what kind of sealing has been used

noreply@blogger.com (Anne Deacon Juhl) — Tue, 16 Mar 2010 20:36:00 +0000

An earlier post explained about a couple of sealing methods. This post will give an idea of how to figure out what kind of sealing your product has been sealed with.

If chromate and dichromate sealed there will be a high concentration of chromate ions in the mouth of the pore.

Boiling water makes the anodic coating crystalline, addition of nickel salt (nickel acetate) used as a fix to prevent bleeding out of dyes. These are hydrolysable metal salts, absorbed into the coating where they are hydrolyzed and precipitated as hydroxides, plus if dyed a chemical reaction between nickel and the dye molecules will happen to form new metal complex.

Conversion of Al2O3 to boehmite only occurs at temperature of 80°C and above, pH lower than 4.5 leads to no conversion of aluminum oxide to boehmite. The formation of the crystalline boehmite depends upon coating thickness, pore diameter and requirements of sealing test specification. The three important parameters when hot water sealing are:

1. Water temperature
2. Sealing time
3. pH of water

The chemical composition of Al2O3 is a complex amorphous oxide with approx. 15% sulfur incorporated.

Al2O3 72%
H2O 15%
SO3 13%

When Hot Nickel Acetate (NA) sealing is used the chemical composition of this coating will be almost identical but with a small amount of nickel incorporated (around 1 – 2%).

The Cold Sealed Nickel Fluoride (NF) is a totally different process, an impregnation process (read more)

The chemical composition of the coating will be as follows:

AlOOH
Ni(OH)3
AlF6

Nickel uptake in the anodic coating is a function of pH and the presence of fluoride aids the precipitation of nickel salts in the film.

So to find out if the sealing is a NA or NF sealing you have to do some EDX measurements of the surface. You will find a small amount of Nickel in the oxide film if the parts are hot nickel acetate sealed and a higher amount of nickel, plus fluoride in the cold sealed parts.

Most alloys have no influence on the EDX results but if you have an alloy with high silicon content you will find silicon too in the coating.

If you find this article useful and you would like to know more about my consulting services contact me at blog@aluconsult.com
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Research project about Pulse Anodizing in Spain

noreply@blogger.com (Anne Deacon Juhl) — Tue, 09 Mar 2010 07:35:00 +0000

Cemitec, the Research and Development Center in Navarra, Spain has a Chemical Engineer working in a research project related to pulse anodizing of aluminium.

It is always wonderful to see other people working with something you find important. The work I did in my PhD project was a comparison of various pulse methods and also verifying the use of square wave formed pulses when hard anodizing different alloys.

The project in Spain will also look at the influence of pulse anodizing in the final color of aluminium pieces.

Hopefully Cemitec will present a paper at one of the anodizing events this year. The two anodizing events in 2010 are the IHAA symposium in Las Vegas and the AAC conference in Montreal.

If you find this article useful and you would like to know more please contact me blog@aluconsult.com
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Informative site about aluminum alloys

noreply@blogger.com (Anne Deacon Juhl) — Thu, 04 Mar 2010 19:11:00 +0000

In an earlier post I gather a lot of different aluminum and anodizing website, see Aluminum and Anodizing pages. This is one of them and I just wanted to share one of them, aluSelect. This site is probably the easiest way to find and compare different aluminum alloys. The machinability, composition, anodizing properties and a lot of other technical information about common aluminum alloys.

The two tables below show the corrosion and anodizing properties of 6063 and 2024, respectively. Take a look and be amazed.

If you find this article useful and you would like to know more please contact me blog@aluconsult.com
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Things to remember when placing cathodes in the anodizing tank

noreply@blogger.com (Anne Deacon Juhl) — Wed, 03 Mar 2010 08:30:00 +0000

When a current passes through an electrolyte where aluminum is anode, the negatively charged anion migrates to the anode where it is discharged with a loss of one or more electrons. These electrons need somewhere to go, so they will flow to the cathode for hydrogen evolution.

The anodizing process needs these cathodes to run. So anodizing consists of two processes an oxidation process (anodic reaction) and a reduction process (cathodic reaction), and both of them are necessary to run the anodizing process but most of the time we actually neglect this second reation, the cathodic reation.

When anodizing in sulfuric acid the major cathodic reation is the hydrogen evolution.

The position of the cathodes (the blue parts in the drawing) in the anodizing tank is very important.

The Anodizing solution has a good throwing power compared to most plating solution. The reason for this is the high electrical resistance of the aluminum oxide film. This high electrical resistance will produce an anodic film on both sides of a sheet of aluminum close to a single cathode.

So in theory there shouldn´t be any problems placing the cathodes where they fit best in the tank. The film formation starting on the back side as soon as the resistance between the cathode and the near side is equal to the resistance between the cathode and the back side of the plate.

Even so you will often find thickness variation on complicated shapes and over large complex loads. The reason for this is often an insufficient agitation in the tank, or cathode placed in areas where there never are any parts to be anodized.

For example cathodes sticking deeper into the tank than the work load. This will increase the growth in the lower area of the parts being anodized.

The most common cathode material is aluminum, where the prefered aluminum alloy is AA6063 T5 or T6, or the aluminum alloy 6101 also in T5 or T6.

The placement of the cathodes is along the tank sides, so as much as possible of the cathode is facing towards the anode. The cathode area/anode area ratio should be as close to 1:3 as possibly.

The depth of the cathodes should not exceed the maximum length of a normal work load.

Joints between the cathode and aluminum bar should be as easy to maintain as possible because aluminum and the sulfuric acid reacts to form aluminum sulfacte which is very voluminous. This corrosion product can force the cathodes away from the aluminum bar with the loss of contact between the two.

If you find this article useful and you would like to know more about working with me please contact me blog@aluconsult.com
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Color variation in hard anodizing of five different aluminum alloys

noreply@blogger.com (Anne Deacon Juhl) — Thu, 25 Feb 2010 20:51:00 +0000

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The picture to the left shows five different sand cast aluminum alloys.

From left AlSi7Mg0,3, AlCu4Ti, AlSi5Mg, AlZn5 and AlSi0,5Mg.

The five alloys have been anodized under the same anodizing condition on separate loads.

The reason for the color variations are due to the different microstructures in the five alloys.

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

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Glossy or matt aluminum

noreply@blogger.com (Anne Deacon Juhl) — Tue, 23 Feb 2010 23:11:00 +0000

If you like glossy materials, special aluminum of course, you should take a look at this blog http://achromaticphenomena.blogspot.com/ where Richard Karsten works on a book "Beyond Color: Achromatic Phenomena," a book exploring the attributes that affect the way a surface or object appears, such as gloss, luster, transparency, luminosity and iridescence. You can share your ideas there and participate in the conversation about achromatic phenomena in design, art and nature.

Well, very interesting - this is a woman’s thoughts - glossy is definitely eye-catching, new and valuable, pure, untouched and clearly a reason for the diamonds and gold obsession you see.

In the aluminum world I see a trend towards the more matt surface again after 5 - 10 years with high gloss anodized surfaces. The reason – well, in my opinion, is the new simple living lifestyle where back to basic is good. So matt aluminum surface is probably more trendy now because it actually shows us the real world.

If you find this article useful and you would like to know more please contact me blog@aluconsult.com
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Metal Finishing trade associations work together with SFA and AluConsult to increase the knowledge in the finishing industry

noreply@blogger.com (Anne Deacon Juhl) — Sun, 07 Feb 2010 21:15:00 +0000

The two trade associations, the Metal Finishing Association of Northern California (MFANC) and the Metal Finishing Association of Southern California (MFASC) are announcing their 2010 Supplier Showcase taken Tuesday and Thursday, February 16 and February 18.

February 16, 2010
SUPPLIER SHOWCASE
Quiet Cannon
Montebello, CA
4:00 PM - 8:00 PM

February 18, 2010
VENDOR SHOWCASE
Nepredak Hall
San Jose , CA

The Surface Finishing Academy will host the second anodizing workshop at the Embassy Suites - Silicon Valley coinciding with the annual MFANC Supplier Showcase Night in San Jose. The MFANC event will immediately follow our workshops on February 18th.

All SFA students will receive complementary general admission to the Supplier Showcase, and MFANC members may receive a 10% tuition discount for either of our San Jose courses. Please contact Paul Fisher at the Surface Finishing Academy if you have any questions or need more information.

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

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Chromic Acid Anodizing

noreply@blogger.com (Anne Deacon Juhl) — Fri, 05 Feb 2010 08:23:00 +0000

As told in an earlier post regarding different anodizing electrolytes, the Chromic Acid Anodizing, CAA, was the first commercial anodizing process patented in 1923 by Bengough and Stuart.

Chromic acid anodizing is mostly used for protection of critical structures with all kinds of joints. The corrosion resistance is excellent relative to the thickness of the coating, which normally lies in the range of 0.08 – 0.2 mil. The oxide film is softer and less porous than those formed by the other processes, and is formed without any significant fatigue loss of the material. The film is easily damaged and the color is light opaque gray. When this film is sealed in a dichromate seal a greenish color appear.

The process is voltage controlled with a ramping in the beginning of the process increasing up to 40V depending on the type specified. Two types are specified in the military specification MIL-A-8625F, Type I and Type IB, whereas the first is conventional coatings produced by a voltage of around 40volts and Type IB uses a voltage of 20 to 22 volts.

Other specifications are AMS 2470 and ASTM B 580 for Chromic Acid Anodizing.

The anodizing process steps for Chromic Acid Anodizing are usually more simple than the ones for the Type II anodizing (SAA = sulfuric acid anodizing). The work should be cleaned by vapour degreasing and if necessary an additionl alkaline cleaning. After a final rinse in clean water the work should be ready for anodizing.

Different customers call out different process parameters which sometimes makes it difficult to handle a variety of customers.

Some of the various customer specifications are:

Boeing BAC 5019
Cessna CSFS020
Eclipse EAC1006A
Bombardier MPS160-10

The main use of Chromic Acid Anodizing is due to the fact that residues from the chromic acid trapped in parts that are difficult to rinse does not lead to corrosion. Another important feature is the fact that Type I coatings keep the aluminum materials fatigue strength and the very thin layer makes a minimal dimensional change.

Alloys are not allowed to contain more than 5% copper or 7% silicon, and total alloying element must not exceed 7.5% according to MIL-A-8625F. The alloys should be in one of the following temper before anodizing, T4, T6 or T73.

The electrolyte should consist of 50 - 100 g/L chromic acid and with a temperature of 95 - 105F. The purity of the chromic acid should not be less than 99.5% CrO3. Chloride is the worst contamination for the electrolyte and shouldn´t exceed more than 20 g/L. Chloride present in the electrolyte causes etching of the aluminum.

The hexavalent chromium content, the free chromic acid, decreases during the process and the trivalent chromium and aluminum increase.

Most of the Chromic Acid Anodizing is processed at 40 V, the low voltage is only used for special alloys which are difficult to handle at the higher voltage, as e.g. 2014 and 7075. Ramping is essential is this type of anodizing.

An easy way to remember the ramping time is the following;

For the all the alloys using 40 V, use 40 minutes to increase the voltage to 40V and then anodize for another 30 minutes. For the alloys using 20V, the same pattern can be used, use 20 minutes to get to the 20V and then spend another 30 minutes at that voltage.

The two different voltages used for Type I and Type IB create a slighty difference in the oxide film formed which can be seen in SEM images below of the surfaces.

Type IB, 22Volt

Type I, 40 V

The specifications for the performance of the coatings are a little different than for hard anodizing but the same procedures should be used. The difference is the weight of the formed coating which should be min 200 mg/ft2 and the coating should pass 336 hour in a salt spray test for Type I coatings.

It has to be mentioned that hexavalent (CrVI) compounds, often called hexavalent chromium, exist in several forms. Hexavalent chromium is recognized as a human carcinogen via inhalation. For more information check out, United States Department of Labor or The European Union directive, Directive 2002/95/EC.

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

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