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topic 33883

Problems in Plating on Aluminum


A discussion started in 2005 but continuing through 2018

2005

Q. Our plating supplier is having a difficult time plating a decorative aluminum part (die-cast ADC-12 material, part size 2.4" H x 5.4" W x 9.1" L, nominal wall thickness 3-5 mm, part weight 570 grams). The final plated finish is an antiqued Brass or Nickel, but we are rejecting 31% of finished goods in IQC inspection due to some pitting and white "chalky" material build-up in corners of the parts. The plating supplier is blaming the pitting and chalk build-up on the die-cast suppliers materials, saying that the material is not pure. The die-cast supplier claims that the material is ADC-12 (not recycled) and the parts arrive at the platers with a mirror polish/buff finish (no visible pitting). The problem is I don't know enough about the plating process to solve the problem ... is it the material, is it the plating process, or a combination of both? According to the plater here is the process for the finish on the aluminum part:

1. Clean (ultrasonic)
2. Rinse x 2
3. Nitric Acid bath
4. Rinse x 2
5. Aluminum Sealer bath (quick dip, chemical bath, no current)
6. Rinse x 3
7. Neutral Nickel bath
8. Rinse x 3
9. Semi-gloss Nickel bath
10. Rinse x 1
11. Gloss Nickel bath
12. Rinse x 3
13. Brass bath
14. Rinse x 3
15. Black Nickel bath
16. Rinse x 2
17. Color Sealer bath
18. Rinse x 2
19. Pure Water Final Rinse

I questioned why the plater used Nickel, not Copper, as the first base metal plating bath (my experience in the past has always been Copper first). He said that 'Neutral Nickel' is best in this application. Based on the above process, is there anything that stands out as a potential culprit regarding the pitting & chalking issue? For now the work-around is to use a heavy Copper bath, post polish, then proceed with the Brass plating process.

Edmund Farmer
lamp mfgr. - Stamford, Connecticut, USA


2005

A. I have no idea what an aluminum sealer dip is. Without a zincate step, I am surprised that you do not have an adhesion problem. Zincate followed by an alkaline electroless nickel is an excellent process for aluminum.

James Watts
- Navarre, Florida


Second of two simultaneous responses -- 2005

A. The preplate cycle seems to be wrong. If the Aluminum is a casting, then your nitric acid is not good enough. You have to add fluorides as well and for some casing should include also sulfuric acid!

Aluminum sealer - not familiar with this very odd term. It should be a zincate! On top of it, one should use a double zincate, meaning the first dip 60-90 sec, a dip in CLEAN 50% nitric acid and then a second dip in the zincate for 15-25 sec.

Neutral Nickel - what is it? It should be a neutral electroless nickel or a cyanide copper. There are some special zincates that enable direct nickel plating but it is not always safe.

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel



2005

A. Process seems strange with so many nickels.

Also color buffed aluminum has oil in it, that may come out in plating process, but normally shows as bad adhesion.

Light blisters are normally a sign of zinc.

Pitting may be excessive brighter,excessive air, or tank contamination.

Whiteness may be burn if it is on high spots and outer edges nearest anodes.

blisters from air are normally on undersides. If all over check brighteners.

Steve Clark
polishing - Belfast, Maine, USA


2005

A. Edmund, in ADC-12 aluminium alloy there is a high content of silicon; therefore the job shop must use ammonium fluoride to dissolve the contaminants after the alkali pickling. I can see also that he use nitric acid; that's nice. He also uses a sealer which I believe is a zincate. I think the problem can be solved by a dip in ammonium bifluoride solution.

anders sundman
Anders Sundman
3rd Generation in Plating
Consultant - Arvika, Sweden



2005

A. Hi,

Edmund, we have similar problem with decorative plating on aluminum parts (small aluminum cast). We apply instead cyanide copper electro nickel (pH 5,0 2-3 A/dm2). Probably our Ni-bath is like yours, neutral Ni-bath.

Our process

1.clean
2.rinse
3.alkali pickling (temperature 80 °C, NaOH )
4.rinse
5.Nitric acid + 10%HF
6.zincate bath
7.rinse
8.nitric acid wo/HF
9.zincate bath
10.rinse
11.Ni bath pH5
12. rinse
13.gloss Cu bath
14.rinse
15.gloss Ni bath
16.rinse
17.Cr bath

We had a problem with pitting on finished parts . Too deeply polished parts (inside, the casting had different structure) and too high pH in the first Ni bath were the reasons of pitting. Furthermore we changed the air stir in the first Ni-bath. Air strongly mixed the bath and exactly flows around the parts.

Best regards

Waldemar Tomankiewicz
- Krakow, Poland


September 20, 2008

A. Dear Farmar,

I hope sealing of aluminium means zincating.
Plating Aluminium which consists silicon requires a very precise degreasing and rinsing. First see that your cleaners should be non silicated. Be sure of even your desmutting and re-zincating. See that your cleaning chemicals are not etching the die castings. I agree with other platers, you can sure some etchants with nitric dip, only for proper bonding of zinc on your job.

There are many platers who are plating direct Semi Bright Nickel over zincating, but your metal seems to be not fit for this process. Some metals are difficult to plate but not impossible. I suggest, use Copper Cyanide and Bright acid copper after zincating. Since these Copper has a good adhesion and good leveling properties. I think your metal requires uniform leveling and uniform throw all over the current densities after zincating.

For pitting, if your hull cell and other analysis of you baths are ok, then I recommend please concentrate on your pretreatment, quality of rinsing water, proper maintenance of your electrolytes, timely clear out contaminations, organic as well as inorganic and filtration. And sometimes your metal supplier may filling the pinholes, jalla and sori defects by impregnation which gets clear when you degrease them or dip in acid.

All The Best!

shafiuddin ahmed
Shafiuddin A. Mohammed
     metal coating shop
Dubai, United Arab Emirates


April 3, 2013

A. Hi again,

I read Edmund's letter. He is zincating on casting aluminum two times. That will build a bridge on casting aluminum and involves bad rinsing water and contamination from the pretreatment steps in the aluminium substrate. Pure aluminium is an alloy; there you can use 2 and 3 zincating steps, but never on casting alloy.

Regards

anders sundman
Anders Sundman, 4th Generation Surface Engineering
    Sundman & Nylander AB
Arvika, Sweden


sidebar
August 10, 2014

To Anders Sundman,

Good day sir... a point of clarification if I may...
You posted a response in this thread a statement that caught my attention when you wrote this: Quote:

"Pure aluminium is an alloy; there you can use 2 and 3 zincating steps, but never on casting alloy."

I have to disagree with the first part of this sentence when you write that pure "aluminium" is an alloy because in fact it is not an alloy. it is a metal element which just happens to be the most abundant and the third most common, comprising of roughly 8% of the Earth's crust.

No, it is not an alloy. "Aluminium" is an element and is a metal on the periodic table of elements with the symbol Al.

In its pure form it is not very useful for forming into structural material, so it is mixed with other elements to make alloys which are more useful. Almost all aluminum used for aircraft parts or car parts or other structures is an alloy. There are numerous varieties of aluminum alloys available to the design engineer.

It should also be noted the correct spelling and pronunciation is "Aluminium" Not "Aluminum" as my American counterpart has liberally put above. There is no such element as "Aluminum" on the periodic table.

Sir Humphry Davy proposed the name aluminum for the metal but this broke the standardisation of names for that particular group of elements and the correct name was deemed "aluminium" This spelling is in use in all countries apart from the USA and small pockets of her neighbouring nations.

Aluminium was the spelling/name in the U.S. until 1925, when the American Chemical Society officially decided to use the name aluminum instead for reasons known only to them, much like the American date system...

As far as the second part of that sentence is concerned, I cannot honestly agree nor disagree with it because I truthfully do not have enough knowledge and experience in the finishing aspects of metal plating to do so.

I am an educator first and fabricator/craftsman of various metals for over 40 years now. And I make a point to comment when I read something that I feel is incorrect by first confirming the validity of my understanding of the facts and if they are correct, I post them not to berate the original poster but to make sure that when students or anyone else for that matter, come to the various forums which I participate in, that they receive the correct facts. However, I take great pains to make sure that I'm correct so that I'm not blowing any smoke out where the sun doesn't shine if you get my drift.

So please do not take my response as a challenge because I'm not challenging your integrity or your experience here. I'm simply correcting and stating a fact.

Respectfully,
henry

Henry V. Cabrera
- Pittsburgh, Pennsylvania


August 2014

thumbs up signHi Henry. Thanks. This site serves many people for whom English is a second language, including Anders. When they make grammar or spelling errors in postings I try to fix them, just as I edit typos and spelling errors made by posters whose first language is English. But sometimes, limited by the pressures of time (this site has a quarter million postings and the curator/editor is but one person), I'm not quite certain what a poster is saying, so I don't edit it because it might make the situation worse by misstating their thoughts.

I am 100% sure that Anders realizes that pure aluminum is not an alloy. And now that I concentrate on this one particular posting I can see that he was trying to say that the aluminum alloys which are rather pure can accept double or triple zincating, whereas casting alloys cannot (probably because the HNO3 dip implied between the two zincates attacks the other ingredients in casting alloys too aggressively).

Thanks also for the illuminating info on the origin of the words "Aluminum" and "Aluminium". Of all the courses I took in college, "Philosophy of Language" was the most fascinating; I share your appreciation of language. But words do morph, and I use "aluminum".

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



March 14, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi there, I have an aluminium high pressure die cast part that is currently electroplated and I'm getting some random issues with surface finish. It looks like there is some chemical reaction happening under the surface coating. Sometimes it looks like pitting other times it just looks like corrosion. It can be wiped off, but sometimes reappears when it is outdoors for a long time.

The alloy is ADC10 and the process we are currently using is:

- Ultrasonic Wave Cleaning
- Zincate (displacement Reaction) 0.5 - 1µ
- Ni Plating 5 - 10µ
- Cu Plating 20 - 30 µ
- Ni Plating 5 - 10 µ
- SnCo Plating 0.05 - 0.1 µ
- Cr3 Plating 0.15 - 0.2 µ

I was wondering if there was a process to put the cast parts through before the plating process.

Do you have any advice to prevent this type of surface defect?

Many thanks,
Mike

Mike James
- Sydney, Australia


April 1, 2013

A. Hi,

I think the ultrasonic cleaning can do that as the plating can build a bridge over the aluminium area, and in the aluminium substrate some pretreatment will stay left.

Regards

anders sundman
Anders Sundman, 4th Generation Surface Engineering
    Sundman & Nylander AB
Arvika, Sweden



April 8, 2013

Q. Hi Anders,

Thanks for the response. Do you have any suggestions as to how to eliminate this issue. It's actually very similar to the chalky effect that Edmund references in his first post.

Any help would be greatly appreciated.

Regards,
Mike

Mike James [returning]
- Sydney, Australia


April 9, 2013

A. Hi Mike,

Cast aluminium should only be zincated one time, and also take care when you etch the parts. Both etching and zincating will make some pores in casting aluminium. And in the pores it will involve dirty contamination from the pretreatment steps. Also the pretreatment steps are important because of what is in the alloy in the aluminium casting.

Try to translate on the library here on finishing.com what I have written about aluminium.

Regards,

anders sundman
Anders Sundman, 4th Generation Surface Engineering
    Sundman & Nylander AB
Arvika, Sweden



April 10, 2013

A. It may be porosity in the casting that is causing your problem. A possible solution is to try a double zincate process. Or, if it is porosity related, then baking the parts at low temperature before plating, or an anaerobic sealant may help.

Lyle Kirman
consultant - Cleveland, Ohio


April 18, 2013

A. Cast aluminium is a problem to electroplate and needs to be carefully treated, because solutions can get trapped in the porous structure of the casting. Firstly, you need to treat the casting with a zincate treatment and then I would suggest you fill the pores and bridge any surface spaces with a high throwing power copper. The thickness of the copper will in part depend on the casting porosity. I am not convinced that nickel will have adequate throwing power and if you are using a nickel strike, it will probably be based on chloride, which is a potential disaster area for uncoated aluminium. You should also ensure the parts are extremely well washed between these initial stages and as Anders says, ultrasonics may be beneficial.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK



EN plating on aluminum parts with copper inserts

April 17, 2014

Q. Hello:

We have some parts that are manufactured out of 6061 AL, with integral Tellurium Copper inserts. Imagine a .5x6x6" piece of AL, with a 2x2" center section made of the Te-Cu, with a seamless transition from the AL to the Cu (no gaps). The customer wants to electroless nickel plate the entire part. My concern is the different pre-process requirements for AL vs. the copper. Can this be done? Anyone have any experience with EN plating of a two-metal part like this? Many thanks in advance for any help!

Joe Osborn
Manufacturer - Novato, California


April 29, 2014

A. Hi Joe. Sorry, I have no experience with this, and can't find reference to it in my texts or on-line. But we appended your inquiry to this thread because I think the process will start with zincating and then copper plating of the aluminum, followed by electroless nickel on everything. Copper is not catalytic to electroless nickel, so you will have to "spark" it first (apply electricity for a second or two).

I'm sure you well know that plating or chemically processing an assembly of different materials is invariably a bad idea -- but if there is no way around it, I think it can be done. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



July 18, 2014

Q. I got some aluminum plating done and it came back discolored and sticky. Does anyone know what went wrong -- was it what I did or the platers?

kurt bailey
- sun valley California


July 2014

A. Hi, Kurt. A plating shop is supposed to do good plating, not discolored and sticky plating, so our first thought must be that the plating shop probably did something wrong. If you can give us some facts like what you did and what you asked the plating shop to do, a less superficial answer may be possible.

Luck and Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



sidebar

Is ADC-12 aluminum non-recyclable?

September 11, 2014

Q. I'm researching a project for work. Can anyone tell me if ACD-12 aluminum is recyclable or has any conservation benefits? I see some areas it is, and others it's not.
Thank you!

Melanie Gann
- Lewisville, Texas


September 2014

A. Hi Melanie. According to benefits-of-recycling.com/aluminumrecyclingprices/, aluminum castings are one of the more valuable forms of aluminum for recycling. There may be some problem with ADC-12 but I'm personally not aware of it. Where are you seeing this info that suggests that it is not recyclable? Thanks.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


September 12, 2014

Q. Hi Ted,
Thank you for your response. When I'm researching, everything relates back to aluminum beverage cans and recycle and conservation benefits for them. I cannot get a clear answer on cast aluminum or ACD-12. Does it break down the same and can I use the same stats/facts, or is this a completely different type of material?
Thank you!
Melanie

Melanie Gann
- Lewisville, Texas


September 2014

A. Hi again. I don't know what you mean by "break down the same", and sorry but there's no way anyone can say whether you can "use the same stats/facts" when we don't know what stats you want to apply or to what circumstance you want to apply them. Clearly you won't find stats showing what percentage of people put their broken ADC-12 castings from their old cars in with their cans and cardboard for curbside recycling; still, they may well take them to the scrapyard; and manufacturers of castings probably have regular arrangements for recycling.

Please do your best to explain the details of your situation :-)
Thanks!

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



What does "Zn Coverage" mean in Plating of Zn on Aluminum Extrusions

April 7, 2015

Q. What exactly is meant by Zn Coverage on Aluminium Extrusions? What is it unit for measurement and how it can be measured? Will an EDXRF do this job?

Raghunandana Subbanna
Customer Support Engineer - Bangalore, India


April 2015

Hi Raghunandana. Either of us can look up the word "coverage" in a dictionary, but it doesn't help, does it? Sometimes it might refer to a requirement that there must be visible zinc plating everywhere on the extrusion, with no bare spots; sometimes it might dictate a replenishment schedule of how much zincate to add for every 1000 sq. foot of extrusion processed -- just as you might read on a quart paint can that it offers 100 square foot of coverage.

Unfortunately it is nearly impossible to have any assurance what some third party meant when we hear two words transcribed out of context like this. At this point neither of us knows what the requirement is, so it's not possible to say whether an EDXRF is of any value in determining compliance. Please try to figure out and explain the exact situation. Thanks.

Regards,

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



March 17, 2018

Q. I'm going to manufacture a die-cast A360 Aluminum part in China and they are telling me it can't be coated with clear zinc because the temperature of the zinc is too hot and it will disfigure the part. It's a housing part that will be matched up with a T6063-T5 heatsink which is going to be anodized. Can the part be coated with a clear zinc coating? Thank you in advance.

Gary Taverrite
- Sacramento California USA


March 2018

A. Hi Gary. What function or process do you have in mind when you say "coated with clear zinc"? Even without language translation difficulties, "coated with clear zinc" sounds like it might have led to misunderstandings :-(

When *I* hear that phrase, I envision electroplating with zinc (which is silvery metallic in color, not clear) followed by a light blue or "clear" chromate conversion coating so the luster of the zinc plating is retained. Zinc electroplating and conversion coating is not a high temperature process, but others might envision something else.

I also have a little bit of a problem interpreting what you mean by "matched up with". Do you mean that you want the "coated with a clear zinc" part to look similar to the anodized part (it won't), or do you mean they will be connected together (they are not very galvanically compatible).

Regards,

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


March 18, 2018

Q. Hi Ted - thank you for responding. Here is what it says on the drawing from my US customer.

MATERIAL: ALUMINUM A360 OR EQUIVALENT
FINISH: LIGHT SAND BLAST, CLEAR ZINC. ROHS COMPLIANT


I'm not sure how to interpret my China manufacturer's statement that you can't coat aluminum with a clear zinc costing. Furthermore my customer wants to know if I can get him samples of aluminum coated with the clear zinc in varying thicknesses -light - medium - heavy.

Sorry I'm a bit of a neophyte on this process. Thank you.

Gary Taverrite [returning]
- Sacramento California USA


March 2018

A. Hi Gary. The drawing note doubtless means, as I described, zinc electroplating followed by RoHS-compliant clear trivalent chromate conversion coating. You can get a copy of ASTM B633 [link by ed. to spec at TechStreet] to understand all this better (although that spec actually covers zinc plating of steel rather than aluminum), and you will probably then interpret light, medium, and heavy as 5, 8, and 13 micron thick coatings.

However, it's possible that your customer is also a neophyte and is hoping for a voice of knowledge & experience to chime in before the parts are plated. It doesn't sound like your manufacturer in China will be offering anything remotely like that (perhaps you're dealing with a broker of some sort rather than a knowledgable plater). Further, although it is certainly possible to zinc plate aluminum, it is a rather unusual finish. So it might be a good idea to phone your customer and understand each other a bit better. At the risk of being called jingoistic, I might also suggest that you consider getting those samples plated in California, where every plating shop understands that drawing note :-)

Luck and Regards,

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


March 19, 2018

thumbs up sign Thank you Ted. That is good advice and helps a lot.

Gary Taverrite [returning]
- Sacramento California USA



Pits in nickel-chrome plating on aluminum

October 17, 2018

Q. Hi,
I'm working on a project for my company where they plate Aluminium parts, but there is a problem with the plating. The finished product has all throughout the part little specs and some pits. We've tried different processes and checked if it was in the substrate or not, sometimes the pits where in the substrate and not in the plating, but mostly it is in the plating.
The alloy comp is a 6060 Al. Any idea what the problem could be?

Process is described here:
1.soak
2.rinse
4.rinse
5.soak
6.rinse
7.rinse
8.etch
9.desmut
10.rinse
11.rinse
12.zincate
13.rinse
14.strip
15.rinse
16.zincate
17. nickel strike 6v
18. semi bright Ni
19. high sulfur Ni
20. bright Ni
21. MPS
22. chrome activator
23. chrome bath.

Best Regards,

Jacob Lopez
metal plating - Noord-Brabant, Nederland



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