Poor Nickel plating adhesion to 1050 spring steel

[Bottomfeeder]

We are providing an assembly to our customer which has a simple 1050 spring steel L bracket adhered to glass with 3M 5915 VHB adhesive. The bracket is the designed and spec'd by our customer. We are purchasing the bracket from their supplier and using it in the assembly.

Initially, the brackets did not spec a plating of any kind - bare steel. These came in very dirty (oil, rust, oxidation, etc) and were completly unsuitable for adhering with the VHB.

The issue was brought up, and the spec was changed to include: Nickel Plate, Min thk 10um, finish to conform to ISO std. 1458 Fe/Ni10b.

This has resolved the cleanliness issue, but we have seen some plating adhesion issues. In some cases, moderate tension (tugging by hand) applied to the mounted brackets results in complete failure of the bond between the base metal and the plating on the entire mating surface.

A corrective action has been sent to the supplier. Their recommendation is to change the plating process to "autocatalytic nickel plating according to ISO 4527"

While I have minimal experience in plating, I question the validity of this solution. Everything I have read indicates surface preparation and proper plating chemistry have the biggest impact on adhesion.

Is there something about the autocatalytic nickel plating process that produces better adhesion over the current process?

 

[IRstuff]

So, why not just have them clean the parts for plating and not do the plating? Seems like a lot of expense and trouble to solve what appears to have been a cleanliness problem in the first place.

TTFN

FAQ731-376

 

[TVP]

Bottomfeeder,

I'll refrain from any personal commentary other than to agree that cleaning is of paramount importance. The answer to your question is yes, there is something different about autocatalytic plating (also called electroless) when compared to electroplating processes. Spring steels are very sensitive to hydrogen embrittlement, so they cannot be aggressively cleaned in acid baths, and must be baked after plating, usually at 200 C for 2-24 hours, depending on microstructure, hardness, etc. Electroless processes can be less damaging and may potentially offer a solution to the adhesion problems.

 

[Bottomfeeder]

I've attached a picture of the original un-plated bracket. The parts are coming from overseas, so my assumption was that the corrosion was occuring during transit, and that the part could also benefit from the corrosion protection of the plating.

We rarely deal with stamped metal parts, so I have very little basis for what to expect from a part like this. The few other stamped parts we buy are galvanized steel. I'm not sure if this level of corrosion is is typical with untreated spring steel or not.

Maybe I'm just dealing with a crappy supplier?

 

[CoryPad]

If the original part was untreated, why is it black?

If trans-oceanic shipment is involved, the parts should be cleaned and coated prior to shipment. In the absence of any serious requirements, a simple phosphating treatment could be used instead of expensive nickel plating. You may need to do a second cleaning prior to applying the adhesive.

 

[TVP]

Pure speculation, for what it's worth:

1. Current "untreated" part actually has some type of coating, maybe phosphate + oil, black oxide, etc. The appearance is terrible, and indicates poor packaging conditions for sea transit from China.

2. Some type of coating/plating is necessary for corrosion protection unless rigorous packaging methods are used.

3. You are dealing with a crappy supplier if 3 yahoos from the Internet provide a higher level of customer service, technical problem solving, etc. What type of root cause analysis did they perform? Perhaps you need to work with a reputable third party, possibly a lab like Stork Materials Testing (several sites throughout the USA), Exova (same thing), or IMR, to develop a thorough understanding of the problem.