Plating and metal strength

One point would depend on the process of the plating, if there was heat involved in the plating it could be possible that the properties of the bolt material could be changed, wether making it more brittle, or lower yeild strength would depend on duration of heat and cooling.

The other point would be from a fatuige strength standpoint. While changes in material properties from possible heating/cooiling would also play a role here the surface finish would also have an effect. If the surface of the plating is rougher than the surface of the bolt it will have a detrimental effect on the fatuige life of the bolt whareas if the surface finish of the plating is smoother it will help the fatuige life.

For example, standard decrative chrome plating is one of the worst things that can be done to a part that will experiance fatuige loading, the finish of regular chrome looks like a dry lake bed under some magnification. The presence of those tiny surface cracks provide a propigation point for larger cracks to occur. (There are varying qualities of chrome plating, Industrial chrome plating is used to increase fatuige life whereas decrative chrome is usally detrimental)

69 Rustang said:

This may be a dumb question, but does plating affect the strength of bolts and other parts?

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Powder coating, annodizing (alluminum), and chroming won't effect the strength.

Like mentioned, heat is the factor.. and while powercoating required "baking" of the part, the heat is still low enough not to cause any problems.

The effect of the surface in relationship to fasteners is an interesting point. I've never given it any thought before, but it makes sence.

There are many factors that affect bolt strength such as SAE grade, material composition, size and number of threads per inch. Even if the threading is cut or rolled can affect the overall strength. As said, minor cracks are the worst for fatigue applications since they create stress concentrations. There are charts that display what kind of stress concentration factor to use depending on the finish of a sample. A highly polished sample will have fewer imperfections than an extruded sample and in turn will have lower stress concentrations. However, probably one of the biggest factors in bolt strength comes from preloading, or torquing of the bolt. The more you torque the bolt, the stronger it will be (until you reach a certain point however). In short, plating can affect what the bolt can take or not, but it is not as big as some other factors. I haven't gotten too much into coatings though so this is what I have learned from standard fasteners. Basically, the smoother the surface (more polished I should say), the stronger it will be.

70_Nitrous_Eater said:

Powder coating, annodizing (alluminum), and chroming won't effect the strength.

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actually chroming can affect the strength of a bolt, or other part. during the chroming process you have the real possibility of hydrogen embrittlement due to the process itself. remember that the metal is soaked in an acid bath treatment as part of the cleaning process, and that acid bath, and the subsequent neutralization bath, is where the embrittlement can come in. too long on the acid, and not long enough in the neutralization bath, and when the part goes through the plating process, the acid is locked in, and hydrogen embrittlement begins.

agreed

http://www.tcnj.edu/~rgraham/barrett/manual1-A.html

Cadnium plating is meant for corrosion resistance and is more purposefull than it is decorative but is sometimes used as a base prior to a decorative plating. It is only a few microns thick and the products we have had cadnium plated over the years show no signs of fatigue.

Hmmm.. never considered hydrogen embrittlement, but it makes sense.

I had always thought hydrogen embrittlement was something that took a long time to occur. Whereas chroming can be done in a matter of hours.

hydrogen embrittlement takes less time than you might think, but remember that metals to be chromed are put in a few cleaning baths for more than a few minutes at a time. then they go into a few neutralization baths. if the cleaning solutions are not fully neutralized before the part is plated, hydrogen embrittlement will occur over time.