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How to Chromate Conversion Coat ADC12, 380, Castings, and Secondary Aluminum Alloys

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Q. We had powder coated ADC12 High pressure die cast aluminium. We have done Alodine pre-coat; and after that pure polyester coating of 60 microns. But it is failing to sustain 336 hrs of salt spray test. Can anyone suggest alternate method for corrosion resistance to ADC-12?

Pravin Bhimanavaru
- Pune, India
January 30, 2023

A. Hi Pravin. I think that if aluminum is properly chromate conversion coated and properly painted/powder coated, it should last that 336 hours.

I suggest that you investigate whether the chromate conversion coating process is being done really right. You may need to replace the contents of the tank, or adjust your de-smutting process as discussed in this thread. What do the parts look like after they have been chromate conversion coated but haven't yet been painted?
Salt spray testing is meant to help to keep your process on track; it should not be used to mislead you towards replacement processes, but if you want alternate process recommendations anyway, please tell us about the component and its requirements.
Luck & Regards,

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

⇩ Related postings, oldest first ⇩

Q. I have a problem with chromate conversion coating on 380 aluminum: I have a very trace amount of copper on the surface of parts when the they are put into use down the road. Anyone have any ideas? I am using a thin coating of chromate. Replating of copper? Corrosion of the alloy's copper?

Joe Hanke
engineer - San Jose, California

A. 380 has a lot of copper in it, about 3.5 percent, so I'd certainly assume that the copper is coming from the alloy, and immersion depositing. At this point there is probably dissolved copper in the chromating bath. Whatever you are doing in terms of rinsing after cleaning / etching /desmutting probably needs improvement; but I don't know if that alone can fix the problem, or if the longevity of your chromating solution will be limited by its picking up copper this way.

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

A. My experience has shown that chromating solutions for use with aluminum alloys have to be discarded quite frequently. It usually comes concentrated and takes little to make up. Some good hand scrubbing, caustic etch, rinse, Preposit® 748, rinse and then chromate. This works great for me.

Hope this helps.


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 castings (A380, 413.2, ADC 12, GD-AlSi9Cu3, GD-AlSil2(Cu)).

Thank you,

Kevin Yuskis
- Richmond, Virginia USA

A. Alodine is a trademark of Henkel Surface Technologies. Find them on the web or ask your local plating process distributor if they handle Henkel. This site is made possible by supporting advertisers, and we can't bill to maintain the contact info for their competitors :-)

I don't have a good answer for question #2, sorry, but I do have an excuse: This is a conversion process not a coating process, so it's usually measured by weight rather than thickness. But it is very thin (millionths of an inch, not thousandths).

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

Update Nov. 2006: The domain is still functional but the referenced page link is now broken. Progress has been made on this subject though, and there is now a MIL-DTL-5541 [on DLA] approved hex-free substitute called TCP (trivalent conversion process) licensed by the navy to CST-Surtec, Henkel, Luster-On, and Metalast.
Update Feb. 2020: is now broken and leads to a French site about house building, but there are probably additional TCP licensees by now.

Q. I need yellow Alodize (chromate conversion) technical data for die casting aluminium (ADC12), which shall meet MIL-DTL-5541 [on DLA], CLASS III.

Peter Hong
student - Nanhai, Guangdong, China

A. Hi Peter. To my knowledge there is no product called "Alodize" but a technical dictionary claims --

"ALODIZE: A process for bathing metal in hot Alodine solution to give it protective coating and surface for painting."

So I think this thread about "Alodining" ADC12 covers your topic. Good luck.


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

Q. We have been told that Alodine® can only be used with the so-called "pure" grades or primary aluminum alloys, and that it will not work with the secondary alloys, such as, 360, 380, etc., that are found in the pressure die casting industry. Is this true? I would appreciate hearing from anyone who can share their experiences of Alodining secondary aluminum alloys.

Don Wineman
- Asheville, North Carolina

A. Don, perhaps whoever told you this is not familiar with the diecasting business. We probably Alodine 90-95% of the aluminum castings we run and that would include A380, A360, ADC12, 413.2, etc. Now if you had mentioned anodize, your source of information would be correct.

Kevin Yuskis
- Richmond, Virginia

A. Alodine and other chromates and also anodizing may be applied to the casting alloys you listed. Only the surface preparation is different. In the case of the cast alloys the quality of the finish (either chromate or anodize) is a function of how much non-aluminum alloying ingredients we can remove from the surface, and different preparation for different alloys. Many job shops are only set-up for wrought alloys and when they try to process the casting alloys thru the same deoxidizer they leave alloying ingredients on the surface; then since we can only anodize aluminum, the presence of the silicon, copper, etc, interferes with the cosmetic appearance and the protection of the chromate or anodize oxide.

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

Q. Hello,

We tried to do clear chromate per MIL-DTL-5541 [on DLA] on ADC-12 aluminum alloy casting.
We followed the same process as we do for extruded aluminum. The parts look blackish and we also see lot of big stains on the surface.

Can somebody help me what change in process is required to get a good finish? I heard that others had success and get good quality surface finish.

Thanks in advance.

- Randolph, Massachusetts, USA
March 15, 2013

A. Hi Pritam. We appended your inquiry to an existing thread which answers it. Diecastings contain silicon, copper, and other materials which will cause these problems if not removed from the surface with proper pretreatment chemistry. The etch, and especially the desmut process that you are using, are probably not adequate for castings. Please talk to your supplier about new chemistry for these steps. Good luck.


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

Q. There are so many Alodining types available like Alodine 1000, 1200, 1201, etc. I just want to know which type is suitable for ADC-12 diecasting. Can anyone tell me?

March 31, 2013

A. Hi Abhishek. Alodine is Henkel's trade name for their line of chromate conversion coating chemistry.
Yes, it is confusing because there are many types depending on whether you need a light, low coating with good electrical conductivity vs. a heavier more corrosion resistant coating where conductivity doesn't matter; whether you intend to apply it by spray or immersion dip; whether you want to buy it as a liquid or a powder, whether rinsing is do-able or you need drying in place, whether this is primarily a touch-up operation where you want a single-part concentrate for simplicity vs. a system where you can add replenishment chemicals to maintain a balanced system at lower cost; and whether you can use a hexavalent process or need to use trivalent. Hopefully you can understand why people cannot answer your question without more info. Please tell Henkel or another supplier these additional details about your needs, and they will tell you which of their products to use.

Good luck and Regards,

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

Black shade after chromating on ADC 12

Q. Hi friends

We have an issue of black shade on ADC12 DIECAST PARTS after chromating Alodine 1200.
The diecast parts have black shade.
The diecast parts are machined and glass bead blasted before chromating.
We have been observing that black shades remain after chromating.

Can anyone post your views in this regard?

Dinesh Pilakot
October 15, 2013

A. The issue is with your precleaning. Each of those alloys have either high Copper or Silicon, which when etched with a caustic solution will form a smut of black powder. You will need to use a more aggressive deoxidizer after caustic etch, one formulated to remove those elements. There are proprietary deoxidizers on the market, your Chromate supplier can help, or you could try a Nitric Acid/ Nitric-Sodium Bi-Fluoride Etch.

Paul Slater
- Cedar Rapids, Iowa, USA

Surface treatment problem on ADC 12 pressure die casting -- insufficient salt spray hours

Q. Hi,
I am looking for a process/chemical to be used on ADC 12 castings to achieve minimum 160 hrs. salt spray life. I have tried different process/s but results are not satisfactory. Maybe because of some lubricant being used (graphite based but shifted to water based during casting process). We have used Surtec chemicals but results are not satisfactory. Will shot blasting with Stainless steel balls help improving salt spray life? Please suggest a process to achieve 160 hrs. minimum salt spray life.

Varun Soni
- Faridabad, Haryana, India
March 11, 2015

A. Hi Varun. We added your inquiry to this thread since your interest may be in chromate conversion coating. You say you've tried different processes and you've tried Surtec brand chemicals, but it's not really clear to me what those processes were.

What cleaning regimen did you use to remove the graphite? And did you try chromate conversion coating after that cleaning? Was the chromate the final surface, or did you paint or powder coat it? How many hours of salt spray are you obtaining? Is your desmut step removing all the copper & silicon, or is the surface black? Thanks.


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

Q. Hi,
ADC 12 parts after nitric acid treatment gets blackish in colour. Is it the graphite based lubricant present in pores during casting process or is it due to presence of high copper? Will short blasting with SS shorts before treatment will solve this problem?

13775-1a  13775-1b  13775-1c  13775-1d

Need salt spray of minimum 160 hours with trivalent based chromating. Please suggest a process. No coating is allowed -- only chromate passivation.

varun soni [returning]
- Faridabad, Haryana, India
March 17, 2015


Sir I want the procedure of how to get the silicon and carbon percentage.

tukaram budde
making aluminium alloys - aurangabad india maharastra
March 17, 2015

Alodine 5200 on ADC12 extreme discoloration problem

Q. We have manufactured large Die Cast ADC12 chassis and steel shot blasted them, 30% HCL and Alodine 5200 post treatment that cosmetically well but not RoHs friendly. Now we are doing smaller modules and we glass bead and decrease and then treat with Alodine 5200 but the color has dissimilar wave patterns in it, like the flow of the material and is very ugly. These need to cosmetically look good but not perfect. We tries acid washes pre-treatments but still the same effect. We need some treatment that is RoHs and does not effect the thermal or electrical properties... also not expensive. Any suggestions?

Stuart Ringwald
Engineer - Houston, Texas, USA
June 23, 2017

Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)

A. The problem with ADC12 is the high copper and silicon content, which don't chromate and can form a smut during etching or acid pretreatment. Clear chromate or anodize will not be cosmetic on copper containing castings.

Appearance can be improved by using a fluoride based etch with nitric and HF or ammonium bifluoride to remove the copper and silicon, but cosmetic can still be an issue as the composition is different everywhere in the casting due to cooling rate. Avoid alkaline etching, this will only remove aluminum and concentrate the impurities.

I have also found better results switching to A360 grade casting material that does not contain copper.

Alex Peterson
- Rochester New York

Cosmetic Surface Finish for ADC12

Q. Hi, I am a R&D engineer in the medical device field. I recently got some parts from Malaysia that are die cast with ADC12 or A383. They sent the finished parts with Clear Chromate surface finish but the look is very "unfinished". This is a customer-facing part and is the housing for some motors with an arm and roller that pinch silicone tubing.

Earlier generation was machined parts so the finish was glossy silver and clean.

What will be a good surface finish for my ADC12 parts that can withstand tubing pinches with motors and not have any damage?

Also the customer will be cleaning this part with various cleaning solutions, so the finish needs to not get damaged over time because of cleaning.

Thank you for any help in advance.

Sourabhi Bhujang
Medical Device Company Employee - SAN JOSE, California, USA
February 21, 2020

A. Hi Sourabhi. We added your question to a thread on chromating of ADC12, which (as you will see) contains some hints about improving the appearance. But I'm a bit confused about why, aside from appearance, the chromating was okay on machined parts but not on castings. It certainly would not have had much abrasion resistance even on machined surfaces.

Yes, as an alternative, the component can be anodized for greater corrosion & abrasion resistance (topic 43432 is "Anodizing On Cast Aluminum ADC12"), but (as you will read) you will still likely find the appearance unsatisfactory.

Another alternative is plating the castings -- see topic 33883, "Problems in Plating on ADC-12".

This is a WWW site for the world so I don't like to get overly nationalistic or jingoistic, but attempting a development projects working with a shop half way around the world instead of right in town is doing things the hard way :-)


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

thumbs up sign  Thank you for your response. I should have mentioned previous generation parts were stainless steel machined vs. current die cast aluminum.

I agree with you on your reasoning about parts coming in from half way around the world but unfortunately that was not my decision to make. :)

Again, I appreciate the time you took to respond to this.


Sourabhi Bhujang [returning]
Medical Device Company Employee - SAN JOSE, California

Q. We are using ADC12 for Die Casting. After Shot blasting with SS 20% Chromium, Machining, Alkaline cleaning in Ultrasonic Bath, DM Rinse, DM Rinse, Vacuum Impregnation, Hot Bath Curing for 15 min, Acidic Brightening Again in Ultrasonic Bath, DM Rinse, DM Rinse, Drying. The product develops small black spots , which are hard to remove even with scrub.

Please suggest best method to get proper cleaning and spot free casting. We don't want to Paint the surface.

We want to Clear Alodine the final product, but must get rid of these black spots.

- New Delhi, India
September 4, 2021

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