What's the deal with "quiet" rotors (gray iron, etc) and zinc-plating?

I've noticed on sites like rockauto there are rotors for sale that are described as quiet.
Supposedly there is a type of iron (called "Gray" iron) that has a
different microstructure that is less prone to high-frequency brake-squeel noise, but this type of iron is supposedly what most or all rotors are already made with.
So is this true?
That you can count on your standard white-box, no-name brand of rotors that might cost you $20 - $30 a rotor is already made using the most appropriate type of iron, this so-called "Gray" iron, and that anything labelled as "low-noise" rotors are just throwing that term in to extract a few more bucks from the price?
(This is not about whether or not a rotor is cross-drilled or slotted, so let's not take this thread on that tangent).
Also, I've noticed that there are some rotors that appear to be black in color - not just the edges but the entire rotor. I think these are described as being zinc plated - presumably the plating gets worn away on the rotor surface in contact with the pads. Anyone have any experience with these? Do the areas of the rotor that are black *stay black* over time and hence they don't rust?
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Hadn't heard of these -- can you point to a specific part?
Wikipedia says gray cast iron is the most common cast iron.
--
"Erwin, have you seen the cat?" -- Mrs. Shrödinger

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Joe Pfeiffer wrote:

Put this into a google search:
"Noise Dampening Iron" rotors
You'll find an assortment of online vendors describing rotors with the term "Noise Dampening Iron".
If there really was a different class of iron that had unique noise-dampening properties that cost a little more (or maybe a lot more) than "regular" rotors, I'd love to know about that.
Yes, there are several different types of brake pads, but there really doesn't seem to be different metalurgy when it comes to the rotors. I think this "Noise Dampening Iron" is a marketing gimic.
There might be stainless-steel rotors (which presumably won't rust) but the thermal properties of stainless steel are not optimal compared to cast iron (based on what I've read).
I believe the squeel that I'm getting is happening at the contact point where the pad backing plate rests and slides against the bracket or arm that is part of the wheel hub or knuckle. This arm/bracket is what keeps the pads from being rotated when they grab the rotor. So the full braking force is applied to this contact point, and over time as the pads wear and get thinner, the backing plate moves laterally to a different contact point on the bracket, and over time you'll get a groove forming on that bracket. When you apply the brakes while in reverse and then again when in drive, you'll hear the pads clunk because of the play caused by the groove in the bracket.
This is why there are pads sold with small shims that make up for the bracket wear. But I think even with shims if there is a brake squeel that won't go away, it's happening because of something going on at the contact point of the bracket. If there is some special product designed for that application, I'd like to know. Brake lube doesn't help.
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more)

full

because

designed

if your getting a squeal it is almost always pad related, now you can hot spot the rotors which will make it worse, but it is almost certian it is pad related. take your pads off and sand them, if the squeel is gone for a while you just figured it out. KB
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