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Problems Chromate Conversion Coating Aluminum Castings Q&A

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RFQ: Chromating on Aluminium for SST of 400 hours.
Anybody is doing Chromating to sustain 400 hours of salt spray testing in India.?
We want to do chromating for aluminium diecast components.

Sanjay Oswal
- Pune Maharashtra
November 8, 2022
    privately respond to this RFQ   ^
Ed. note: As always, gentle readers: technical replies in public and commercial replies in private please (huh? why?)

probertEthumb Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert

You'll love this book. has sold 880 copies over the years without ever a single return request :-)

A. Hi Sanjay. I guess there's no harm in asking, but 400 hours SST for castings does not seem reasonable to me.

In real life, what environment will these castings we exposed to? Are any aesthetic requirement imposed (I hope not). Is there a reason you can't paint or powder coat them after chromating? Thanks.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

⇩ Related postings, oldest first ⇩

Q. We are looking to replace our current aluminum deoxidizer used both on chromate conversion and sulfuric anodize lines. Does anyone know of a deoxidizer that does not contain hydrofluoric acid or fluoride salts that does a good job on aluminum castings?


David Yarberry
- Sherman, Texas

A. The main problem with deoxidizing castings is that the casting alloys are normally only 80-90% aluminum, with a large part of the remainder as silicon, which is a remarkably inert element to almost all chemicals except fluoride. When you treat a cast aluminum surface, at least 5-10 % of that surface is silicon. There are two choices: either you etch away the silicon with a strong mineral acid deoxidizer containing fluoride, or in many cases a non-etching dip in dilute nitric acid or proprietary nitric-containing deoxidizer is sufficient, particularly when parts are anodized. It is well known in the industry that cast parts should not be alkaline etched, as entrapment of alkaline materials are almost impossible to rinse out of the casting pores, resulting in the presence of neutralized aluminum salts when the parts are later immersed in acid solutions, and leaching out after the parts are dry. In other words, often a cleaning cycle of non-etching cleaner then deoxidize in dilute nitric is sufficient. Depending on the alloy and finishing requirements, the only other choice is a dip in a strong nitric-fluoride deoxidizer.

phil johnson
Phil Johnson
- Madison Heights, Michigan

A. The good solution for your problem is the Henkel Surface Technology Product Called Deoxalume 1000 System. This product set is ready for use bath, friendly to the user and very efficient for Cast Aluminium from my experience.

yehuda blau
Yehuda Blau
YB Plating Engineering and Quality - Haifa Israel

A. The Deoxalume 1000 system is a patented deoxidizer designed especially for castings. It contains additives which makes it highly efficient, and it turns the castings almost white. When followed by a suitable Alodine conversion coating, it gives remarkable corrosion resistance. It is friendly to the user in the sense that it is easy to control, but be advised that the bath is a very strong mixture of mineral acids and fluoride. It requires an efficient ventilation system with a corresponding fume scrubber. Safety issues involved with the process obviously need to be considered.

phil johnson
Phil Johnson
- Madison Heights, Michigan

A. I agree with Henkel concerning fluorides, but we are deoxidizing casting aluminium, even castings with 12% Si with a microetch. We are using it in a special way and you have to try it yourself if it works on your details. The benefit is, it doesn't contains any fluorides.

Jorgen Pettersson

Q. We would like to have any information about allowed concentrations of fluorides (F, HF) and sulfur-dioxide (SO2) in the air and on vegetation, especially for aluminium industry. Also we are interested in norms and methods for decreasing of F (HF) and SO2 for best environment protection. Maybe somebody can inform us about related links for this question ?

Zeljko Martinovic
- Mostar, Bosnia & Herzegowina

Multiple threads merged: please forgive chronology errors :-)

Information on Alodine for Aluminum Castings


"Alodine" is a Henkel trade name for their line of chemicals for MIL-DTL-5541 [on DLA] chromate conversion coating of aluminum.

Q. I am looking for some information regarding Alodine 1000 and 1500. First the name and contact information for the manufacturer in the US.

Second looking for information regarding the best method of measuring the thickness of Alodine on Aluminum die castings.

Lastly, any information regarding non-chromate chemical conversion processes for aluminum die casting (A380, 413.2, ADC 12, GD-AlSi9Cu3, GD-AlSil2(Cu)).

Thank you,

Kevin Yuskis
- Richmond, Virginia USA

A. 1. Alodine is a trademark of Henkel Surface Technologies. Please use a search engine for the requested contact info; this site is made possible by our supporting advertisers, and we can't ask them to bear the cost of maintaining contact information here for their competitors :-)

2. I don't have a good answer for question #2, sorry. But it is not a coating on top of the aluminum, it is a conversion process.

3. Regarding substitutes, see for a list of the most promising, and to learn the sad news that, when independently tested, no chromate substitute really holds up yet despite all the hype and the desperate search.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Ed. update Nov. 2022: The domain is now linked to a French real estate agent, but the good news is that some non hexavalent chromium conversion coatings are now approved under MIL-DTL-5541 [on DLA].

Multiple threads merged: please forgive chronology errors :-)

Iridite on Alum. Die Castings - dull appearance

"Iridite" is a Macdermid/Enthone trade name for their line of chemicals for MIL-DTL-5541 [on DLA] chromate conversion coating of aluminum.

Q. We have some parts that we have just started die casting in A380 Alum alloy. Previously the parts were machined out of 6061T6 with Clear Iridite and had a nice shiny finish. The die cast parts have an extremely dull gray appearance which we find undesirable. The finisher is the same. Do I have to live with it? Is there a change required to cleaning process? Like acid etch? I need a conductive finish, what other options do I have? Thanks in advance.

Fred Geck
telecomm - Rockville, Maryland, USA

"The Surface
Treatment &
Finishing of
Aluminium and
Its Alloys"

by Wernick, Pinner
& Sheasby

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A. Hi Fred.

Looks like nobody ran sample parts before the company committed to this drastic change :-(
It is far, far, more difficult to aesthetically finish cast parts than wrought parts.

As a first step, you'll probably need a fluoride-bearing acid in your pretreatment to dissolve the silicon in the alloy, which the anodizing shop did not previously need for your wrought parts. But it is hard to say whether just changing the pretreatment can improve the parts enough to meet your standards. You probably need a consultant, or chromate supplier, or shop experienced in A380, to do a quick development project for you to see how attractive the parts can be made.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

A. Dear sir,

Please specify dimension of your part then we can transfer our experiences to you.

Hadi Khosravi
plating and anodizing - Tehran, Iran

A. Hello , we were faced with this problem trying to get yellow color to show up on Aluminum die casts using a certain Macdermid product.

I achieved this by sandblasting the whole part. Depending on the dimensions on your part, this might as well be an alternate way to get your chromate to show up.

Stephane Daniel
- Quebec city, QC, Canada
March 27, 2008

Multiple threads merged: please forgive chronology errors :-)

What causes Iridite Salt Deposits on aluminum castings

Q. Issue: What causes "Iridite Salts" form on aluminum castings and in their blind holes during hot and humid periods? Is it process or chemical related? Will these deposits cause harm and eventual failure to electronic components? My facility is located in upstate New York and several times during the summer months we experience these "Salt deposits" with E-512 Per MIL-DTL-14072 [on DLA].

Rodney C Williams
Quality Tech - Rochester, New York

A. Blind holes and porosity in casting will trap and bleed with changing humidity and temperature and there is very little you can do about it. Keep the castings out of alkali. Clean only in acids. Use a post treatment on top on the chromate like some of the newer silicates, light oils, or one the newer organic "sealing" (not hydrating) type compounds . And finally, have the final chromate rinse "a little yellow", do not try to final rinse in high purity D.I. water, rather dry on a little yellow water. Let us know what happens.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Multiple threads merged: please forgive chronology errors :-)

Cleaning small aluminum castings before Alodine

Q. I have about 16 small cast aluminum casting that need to be cleaned before Alodine. What is a good household cleaner that I can use.

Ronald Engler
Hobbyist - North Charleston, SC,USA
July 11, 2008

A. Try 5% ammonium citrate solution(50 gm citric acid [on eBay or Amazon (adv.)] /1 lit water +some ammonia, pH must be 7).Hope it helps and good luck!

Goran Budija
- Cerovski vrh Croatia

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