No registration or passwords; no pop-up ads -- just aloha, fun, & answers.
(as an eBay Partner & Amazon Affiliate earns from qualifying purchases).
Home /
T.O.C.
Fun
FAQs
Good
Books
Ref.
Libr.
Advertise
 
Help
Wanted
Current
Q&A's
Site 🔍
Search
pub  Where the
world gathers for metal finishing
Q&As since 1989



-----

Stainless Steel vs. Galvanized vs. Zinc Plated Fasteners




I"m having a new pool installed and I don"t know if I should have stainless steel screws or regular screws used in my screen enclosure. Stainless screws are so expensive. What should I choose?

robert montesarchio
- Nokomis florida
April 27, 2021




⇩ Closely related postings, oldest first ⇩



Q. My company is developing an outdoor product line which is primarily made up of 6063-T5 aluminum extrusions. We decided to switch to all 18-8 stainless steel fasteners for corrosion resistance, but there has been some second guessing as to why we didn't decide to use zinc plated steel fasteners. One reason for the questions is because of the higher cost of the stainless fasteners. In our application, a hex bolt is slid into a channel in the aluminum extrusion, and a the assembly is fastened together with stainless steel brackets. The concern that we have is with the potential for galvanic corrosion due to the fact that we have dissimilar materials in direct contact with each other.

My question is, would zinc plated fasteners be a suitable alternate to the stainless steel fasteners? How would the appearance of the bolts (rust) compare to that of stainless over a period of years in an outdoor environment? How much galvanic corrosion would we see with the zinc plated fasteners as opposed to with the stainless steel?

Thanks for any help you can provide?

Scott Liebert
- Milwaukee, Wisconsin
2002


2002

"Fastener Design Manual"

on AbeBooks

or Amazon

(affil links)

A. I have seen stainless fasteners used on architecturally anodized aluminum in outdoor exposure without any substantial problems, and suspect that it will be acceptable. I am a bit confused by your somewhat offhand reference to stainless steel brackets because these would (theoretically of course) cause the aluminum to galvanically corrode regardless of the fastener material, and being bigger in surface area than the fasteners should probably be a bigger concern.

You probably know that, were it not for its toxicity, the ideal fastener material is cadmium plated steel. It is so close to aluminum on the galvanic scale that there is no galvanic corrosion, it is corrosion resistant itself, if thick enough, and it has great lubricity. Nonetheless, cadmium is a cumulative poison, should be reserved for only the most critical applications, and even there is being rapidly phased out.

The next best material is aluminum plating or coating, again because the galvanic potential is zero. You can investigate Ivadizing for vapor deposition of aluminum, or AlumiPlate for electroplating of aluminum. But I fear that you may find the cost unacceptable for anything but airplanes.

All of the above not withstanding, you didn't mention how the aluminum is corrosion proofed, so the question remains a bit open. But zinc plating is not a good idea in my opinion, and I think it will be short lived. Stick with the stainless :-)

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




Q. What is the difference in years of exposure between stainless steel and zinc plated steel? We produce outdoor signs and am considering using zinc plated steel fasteners instead of stainless steel for cost savings. These fasteners are all used to hold down PCB's that are housed inside a waterproof enclosure. The sign is convection cooled so the internal air is continually exchanged with the outside air. These signs are sold primarily in the United States coast to coast.

Greg Schleusner
- Milwaukee, Wisconsin
2003


A. Moving from SS to zinc plating is a big transition. It would be fair to use zinc-alloy plated fasteners with zinc-cobalt or zinc-iron, which will have an equal if not better service life of SS.

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind
supporting advertiser
Bengaluru, Karnataka, India
saify logo
2003



Q. I have heard many different answers from people who seem to know what they're talking about, but I would like to post this simple question here. What are the basic differences between Zinc plated, Stainless Steel, and Galvanized when speaking about fasteners (screws, lag bolts, etc)? How do the manufacturing processes differ, and which is more resistant to water?

Ron Clark
Hardware store employee - Austin, Texas
2003


2003

"Handbook of Hot Dip Galvanization"
by Maass & Peissker

on AbeBooks

or eBay or

Amazon

(affil links)

A. Stainless steel fasteners are made of solid stainless steel, not coated with it. So if the type of stainless steel chosen is corrosion resistant to the environment it is placed in, it can last essentially forever. The better grades of stainless, like 316SS, can hold up indefinitely in most environments. Even 303 stainless is an excellent choice much of the time.

Zinc plated and galvanized fasteners are made of steel with a sacrificial zinc coating. That coating is eventually consumed. Galvanized coatings are almost always several times thicker than electroplated coatings, so galvanized fasteners greatly outlast zinc plated fasteners.

I would like to agree with my extremely knowledgable friend Khozem, but can only do so with the qualification that his answer applies to Greg's question (which he was addressing) -- but not necessarily the general case.

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




Q. My company is producing small gasoline engines; we sell our product to Southeast Asian for the long tail boat. Recently we met a serious corrosion on outside fasteners produced by zinc plating; the material of fasteners is low carbon steel. It is been use for affixing some steel stamping parts and plastic panels. I am not sure if there are some galvanic corrosion between fasteners and other dissimilar parts, considering from cost, do we have any other proper choice or solution?

Nick Lu
- ChongQing China
July 30, 2009


A. Hi, Nick. There are many choices for fastener coatings including galvanizing, organic coating, mechanical plating, electroless nickel plating, zinc alloy platings, aluminum Ivadizing, and so on.

But I'm afraid that I don't understand your question, and don't understand the application in a "long tail boat" -- is this a small boat with a small outboard motor mounted on a long stick-like lever on the back of the boat? You need to determine whether there were or weren't galvanic compatibility issues (and you haven't told us what other metals are involved), and you have to determine whether the plating was defective in this particular case, or whether zinc plating is a bad specification. Zinc plating is rarely sufficient for exposed outdoor use, especially in a marine environment. For underwater use forget it.

No other corrosion resistant coating will be as inexpensive as zinc plating though.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 31, 2009


A. No doubt that Zinc plated fasteners are a cost effective solution. But during the acid dipping process prior to plating Hydrogen will penetrate into the fastener surface and shall remain entrapped due to Zinc plating. This will make the fastener brittle and is called HYDROGEN EMBRITTLEMENT. This will create micro cracks on the surface of the fastener which will propagate over a period of time, which will lead to failure of the fastener after a long time (say 6 months to one year). Hence you need to ensure that the plated fastener has undergone hydrogen de-embrittle treatment prior to use.

SANDEEP VIJAYAKUMAR
- Bangalore, KARNATAKA, India
August 6, 2013



A. Hi. While Sandeep is right that the fasteners -- unless they are cheap unhardened low strength steel -- are subject to hydrogen embrittlement and require baking, and we appreciate that warning ... his post seems to imply that zinc plated fasteners would otherwise be satisfactory. I think they won't be. I feel Nick's poor experience is probably not an anomaly, but what is to be expected from zinc plated fasteners in many situations of outdoor exposure.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 2013




Q. Hello. I am currently reviewing products provided on a large project in Honolulu. The equipment in question will be located semi-outdoors and will be exposed to wind, some rain, and is located close to the Pacific Ocean (Salt Air) as they call it. The specification called for stainless steel fasteners yet the equipment provider took exception to that and is providing zinc/galvanized fasteners and brackets. I realize the Zinc plated fasteners are less expensive, but will the zinc plated fasteners provide the expected 25 to 30 year life span the equipment is expected to last?

Mike Stevens
architect/product designer/regulator - Bellevue Washington, United States
June 11, 2014


A. Hi Mike. Hot dip galvanized coatings are typically several times heavier than zinc electroplated coatings. Hot dip galvanized brackets and fasteners with a heavy zinc coating will probably hold up; zinc electroplated brackets and fasteners will likely not.

If someone wants to offer a substitute to your spec, though, you would probably be best off requiring a specification number for your consideration rather than letting them be loosey-goosey about it with slang. Good luck.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 2014



Q. How corrosion resistant is Zinc Chromate finish? It is an internal component and subject to oily residue as the external components will be more exposed to the salty air and moisture environment?

Mike Stevens [returning]
architect/product designer/regulator - Bellevue Washington, United States
June 11, 2014



A. Hi again Mike. "Zinc chromate" is unfortunately a loose phrase. Some say it refers to the zinc chromate paint/primer [affil links] that was once popular, whereas others will say it means zinc electroplating followed by a chromate conversion coating (zinc electroplating is virtually always chromate conversion coated).

The steel and cast iron innards of automobile engines don't rust -- because oil is not corrosive. Zinc electroplating with a chromate conversion coating is probably suitable for parts that are not exposed to the moisture and salt air, but they won't last if they are exposed.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 2014




Surface treatment of packaging machinery hardware

Q. We make packaging machinery for various industries. Like Detergent, Fertilizer, etc. We use Hardened hardware of Steel ( Low carbon). Can you guide me, what should be the ideal surface treatment for these fasteners?

Vivek Ingle
- Pune, MS, India
July 4, 2014


A. Hi Vivek. Those materials are corrosive, and most plated fasteners will not be resistant. I would consider zinc plating and chromating, then painting the exposed surfaces after assembly with an acid and alkali resistant paint or perhaps epoxy.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 2014



Q. Hi Ted,

I could not understand you.
1. Do you think I should do Zinc Plating and chromating. - If yes, then what will happen to HYDROGEN EMBRITTLEMENT due to Zinc Plating. It will lower the strength of the bolt.

2. You advice that the open surfaces like Head of the fasteners to be painted. But what will happen next time I have to unlock it?

3. What do you think about Hot Dip Galvanizing. If the fasteners are mechanically cleaned by sand blasting or etc., to avoid acid cleaning (and then hydrogen embrittlement)

Vivek Ingle [returning]
- Pune, MS , India
July 8, 2014



July 2014

"Zinc Plating"
by Herb Geduld

on AbeBooks

or Amazon

(affil links)

A. Hi again.
1. Billions of fasteners are zinc or zinc alloy electroplated followed by chromating. Although hydrogen embrittlement is an issue to be dealt with, in most cases it's simply a matter of immediately and properly baking the parts for embrittlement relief.
2. If loosening the bolts for disassembly or adjustment is a frequent thing, painting the exposed parts becomes less practical.
3. It's possible that zinc plating or galvanizing will be reasonably resistant to some of the materials you are handling. But not to dishwasher detergent (which is extremely alkaline), nor highly acidic fertilizers like ammonium sulphate ... and no one can offer a general solution to "etc." :-)

Are stainless fasteners prohibitive cost-wise or strength-wise? If so, I'd just use zinc plated and chromated fasteners and replace them when necessary; it seems that you will be removing them frequently anyway. Good luck.

Regards,

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


Q. Hi Ted,
How will you compare Zn Plating & Zn-Nickel Plating. The Hydrogen embrittlement issue in both cases. But as you said it can be removed with proper baking. But Zn Nickel Plating has got brighter and steady finish,

Vivek Ingle [returning]
- Pune, MS, India
July 19, 2014


A. Hi again cousin. I do not agree that zinc-nickel plating is brighter than plain acid zinc plating. But it is more corrosion resistant (and more expensive).

The idea is that if you add the right amount of nickel (something like 6%), the surface becomes slower to corrode (probably partially due to greater nobility and partially due to "tighter" corrosion products) -- but is still active enough to cathodically protect steel. Yes, hydrogen embrittlement is usually manageable in hard and high strength steels, but not in the very hardest and highest strength.

But zinc-nickel being longer lasting in plain water and slightly salty water, for the reason explained, does not mean that it is necessarily resistant to the chemicals you may be packaging. Good luck.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 2014




Stainless fasteners on zinc plated purlins are corroding

Q. We use stainless steel fasteners on zinc plated purlins and some structures where we use zinc coating/HDG.
My problem is within six months out [there is] fastener corrosion in nut and bolt.
It's galvanic corrosion? How to prevent it?
Any coating there on stainless steel?
It's a passivation problem?
Please help me

Paresh jadavani
- Mumbai, India
August 12, 2014


A. Hi Paresh. It's not galvanic corrosion because stainless steel is cathodic to zinc plating, not anodic to it. I suggest that you double check the specifications for your fasteners as properly passivated fasteners of a proper type of stainless steel should not be corroding. Do you know what type of stainless steel you are using?

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 2014




Stainless fasteners gall -- can we switch to zinc plated?

Q. We manufacture cargo racks for pickup trucks and ship them throughout the U.S. for carrying ladders, lumber, canoes, kayaks, etc. Our truck racks are clamp-on systems, thus our customers frequently put them on and take them off their trucks. Therefore, some of our screws are tightened and loosened repeatedly. We have used stainless steel screws for many years, but have had numerous complaints from people about the screws spalling during removal and having to be cut off. We have supplied customers with grease packets, and instructed them very clearly that grease must be applied, but we continue to have this problem frequently go the great frustration of our customers. Using zinc plated screws with stainless nuts does not cause this problem, and we are thinking of going to zinc plated screws. What alternatives are there?

christopher green
Christopher Green
Truck Cargo Rack Manufacturing - Madera, California, USA
September 8, 2014


A. Have you thought about using a heat cured epoxy based dry film lubricant such as MIL-PRF-46010 [affil link or DLA] ? Using a spin dip application can get you a thin coating on all surfaces of the bolts and nuts that will stay lubricated but doesn't require any preventative maintenance. (Tip: Don't use one that contains carbon black as the graphite will accelerate the corrosion greatly)

While zinc could work as it will provide lubricity, there may be issues with zinc corrosion product that could lock the nuts onto the bolts due to the voluminous nature of the corrosion product.

Justin Brooks
- Rock Island, Illinois USA
September 26, 2014



Justin-
Thank you. I'm investigating that now. It looks like this might be the solution.

christopher green
Christopher Green [returning]
- Madera, California, USA
September 26, 2014


A. This is a common problem if the bolts and the mount that they are screwed into are the same alloy of stainless steel.

It is less of a problem if two different alloys are used, for example, use 316SS for the bolts and 304 for the mating thread.

Lyle Kirman
consultant - Cleveland Heights, Ohio
September 29, 2014


thumbs up signJustin-
You were correct; the MIL-PRF-46010 has worked very well. We have just dipped and baked the liquid onto our screws in our powder coating over. We are using that on all of our SS screws now. Thank you. - Chris

christopher green
Christopher Green [returning]
Truck Cargo Rack Manufacturing - Madera, California, USA
April 26, 2015




Q. Which is the most suitable product (S.S. or Zinc plated ) to fasten galvanized metal (20 ga. z-bars) onto a concrete surface.

Brian Mcgee
- Toronto Canada
October 29, 2014



"Handbook of Hot Dip Galvanization"
by Maass & Peissker

on AbeBooks

or eBay or

Amazon

(affil links)

A. Hi Brian. Best fasteners would be hot dip galvanized if the z-bars are actually hot dip galvanized (I doubt it since the z-bars are only 20 ga.); or zinc plated fasteners if the z-bars are actually just zinc plated (electrogalvanized).

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 2014




Q. Hi,

I'm having issues with the threaded inserts used in some of the plastic components on my motorcycle. The threaded insert appears to be made of Brass and has a hexagonal outer profile. This type of insert is set into the plastic of the air box, fuel tank and some other locations.

The problem seems to be that the bolts are corroding (or in some other way seizing) to the brass insert. When one tries to undo the the bolt from the threaded insert, there is sufficient friction between the mating threads to instead turn the threaded insert inside the plastic housing, preventing the bolt(s) from being removed.

I'm not sure what the current bolts are made from, but it appears to be a some variety of stainless steel. Can you suggest any bolt materials that I might use to prevent this issue?

Note: These particular bolts are not structural or load bearing, just holding on various lightweight plastic bits and pieces.

Kris Hampel
- Sydney, NSW, Australia
November 23, 2014


A. Hi Kris. Before attempting to remove bolts, you should apply WD-40 [adv: item on eBay or Amazon] to the area and tap it to try to vibrate it into the joint, then let it sit for an hour or so. It makes a big difference. When you re-assemble, use some teflon thread sealant. If it's a poor design for a corrosive situation, I think you just want to minimize the problems it causes you, rather than trying a re-design for less corrosion and galvanic issues :-)

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 2014



Good advise from Ted. A dab of anti-seize when reinstalling is a good idea. Plain old Vaseline will do the job.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina
November 24, 2014




Q. We are assembling a green house frame (used) and trying to decide whether to use zinc plated bolts or to go the higher $ for the galvanized. If I correctly understand some of the above conversation, it is technically the same material, but the galvanized is hot dipped and thicker vs. (application type) and a thinner coating. So, the zinc plated might last ... how long? Versus almost indefinite on the hot dipped??

Around here it is approximately double the price for the galvanized, and we are on a tight budget -- so just trying to decide if the zinc would get us going for at least a couple years. . .?

Rachael Hallgarth
Produce Grower - Henryetta, Oklahoma, USA
December 30, 2014


A. Hi Rachel. Yes, zinc plating is galvanically similar to galvanizing but thinner. I think the zinc plating will last at least several years in your non-seaside environment (but don't let pressure treated wood be in contact with it).

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 2014




Q. Hello: we are designing a 28,000 sf pet adoption facility in the Rio Grande valley located in south Texas. We are using a Varco Pruden pre-engineered building. At the front of the building, we will have (3) large 11'-0" high "animal cut-outs" as a design feature. These will be etched out of 1/4" thick mill-finish aluminum with a water jet, then powder coated with a white color.

16063-1a  16063-1b  16063-1c

I had a question regarding the fasteners that would attach the cutouts to the 24GA steel Varco Pruden "Tech Four" wall panel and into the cold-formed steel Z-girt. This area is very humid and we need a corrosion resistant fastener that is compatible with the aluminum, powder coating, and the VP PEB. please see the attached 3D renderings and the diagrammatic section sketch. Thanks in advance for your help. We appreciate any assistance you are able to provide.

Abbie de leon
boultinghouse simpson gates architects - mcallen, Texas, USA
March 27, 2015




Q. Hi,

I am researching on fastener finishes industry. I am just wondering, besides the process involved, what is the real difference between plating and coating. What are the pros and cons of plating vs. coating.

Would appreciate any explanation or references to this.

Thanks and Regards,
Hitesh

Hitesh Kumar
Financial Services - Mumbai, Maharashtra, India
April 20, 2015


A. Hi Hitesh. Those terms are not specifications and it's hard to put a fine point on slang. "Plating" usually is an abbreviation for electroplating, which is the electrodeposition of a metal coating onto a substrate. But coating is a term with almost no delimitations -- fruit can have a coating of chocolate, a road can have a coating of ice, and a fishing net can have a coating of algae or slime.

"Fastener Design Manual"

on AbeBooks

or Amazon

(affil links)

Coatings of metal tend to have better adhesion to metal substrates than paints or plastics do. If a metal plating is anodic to the substrate it can afford it sacrificial protection; if a metal plating is cathodic to the substrate it can accelerate the corrosion if there are scratches or porosity. If there is no abrasion or scratching action, an organic coating like paint will often outlast a metallic coating; if there is abrasion or possibility of scratching, a cathodic metal coating will usually offer more corrosion protection than painting.

High quality organic coatings are probably usually better than plating for wood screws, but often aren't applicable for traditional nut & bolt construction because of clearance issues, vibration, a need for repeated unfastening & refastening or other issues.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 2015




Ultimate corrosion resistance finish for custom set screws

I am looking for the ultimate corrosion resistant material and/or coating to use for custom setscrews we need for our products.

We have a few scenarios and would like to get a single solution if possible, but understand this may not be ideal.

Scenario 1: We have a setscrew going through an aluminium magnesium alloy casting and fastening against a 6106 T6 aluminium extrusion. A 316 stainless setscrew I would think would be the most corrosion resistant but could cause bimetallic corrosion, with the 6106 aluminium. Is there a coating we can use on the 316 setscrew to form a barrier between the two materials, and if there is, is there a worry about cavity corrosion of the stainless setting in? Or could you advise a better material to use.

Scenario 2: We have a setscrew going through a malleable cast iron casting that has been HDG, and fastening against HDG pipe. Again looking for the most corrosive resistance in the setscrew. Is it ok to put a mechanical galv coating over a stainless setscrew? Or again could you advise a better material or coating to use.

Many Thanks

Steve Thrush
- Melbourne Australia
May 5, 2015


A. Hi Steve. I think I'd use the 316SS for the aluminum situation, although you could perhaps order the set screws to be Ivadized or electroplated with aluminum. For the galvanized situation, I'd probably use galvanized steel setscrews. I don't think it's possible to galvanize stainless steel, but it can be electroplated with zinc if you wish. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 2015


? Will the applications allow the use of nylon set screws?
Regards,
Bill

William Doherty
Trainer - Newcastle, NSW Australia
May 8, 2015


Q. Hello Bill, I am interested in your comment on Nylon setscrews. The setscrew is a M12 x 1.75 thread x has to reach and maintain a 30kN holding force. Is there a nylon out there that can do this without stripping the thread or the drive?
Regards
Steve

Steve Thrush
- Melbourne, Australia
May 10, 2015


A. Hi Mate,
I do not have to hand the mechanical properties of nylon fasteners.
Your first point of reference could possibly be a Blackwoods catalogue to identify Aussie manufacturers?
Regards,
Bill

William Doherty
Trainer - Newcastle, NSW Australia
May 19, 2015



(You're on the 1st page of this topic)       Next page >




(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

 
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g, Train'g
& Software


About/Contact  -  Privacy Policy  -  ©1995-2024 finishing.com, Pine Beach, New Jersey, USA  -  about "affil links"