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# Zinc in Brass / Bronze3

## Zinc in Brass / Bronze

(OP)
Does anyone know the origin and use of the Guillet Zinc equivalent factor? I am dealing with a dezincification issue and both the Zn-content and whether the alloy is alpha or alpha + beta are relevant. I have the impression that it is only applicable to the high tensile brasses, but do not really know.
Replies continue below

### RE: Zinc in Brass / Bronze

3
This is a metallurgical 'rule of thumb,' much like the carbon equivalent used for predicting the hardenability of steel, or the Cr & Ni equivalents for stainless steel phases.  Each rule is an semi-empirical method to predict phase equilibria, whereas calculation via thermodynamic principles might be exceedingly complex or limited by lack of data.

Guillet zinc equivalent

With the exception of lead, most of the common addition elements enter into solid solution in brass and the simple binary copper-zinc equilibrium diagram is no longer valid. If it required to estimate whether a brass will be all alpha or duplex in character it is necessary to allow for additions using the Guillet zinc equivalent factor, multiplying the content of silicon by 10, aluminium by 6, tin by 2, lead by 1, iron by 0.9, nickel by 0.8 and manganese by 0.5 using the formula:

Zinc equivalent = (A/B)x 100

where A = sum of (zinc equivalent x % of each alloying element) + zinc

and B = A + % copper

This method gives good accuracy for high tensile brasses provided that alloying elements do not exceed 2% each.

http://www.brass.org/Publicat/pub117/sec63.htm

### RE: Zinc in Brass / Bronze

(OP)
Ummmmm, thanks for the reply, but I had already seen the web page (and am familiar with various equivalents used in C-steels, Ti-alloys, cast irons, etc). I need more information than is readily available on the internet. Who was Guillet and why did he/she develop that formula? Is it for predicting whether the alloy will be alpha or alpha + beta (as is done with the Al and Mo equivalents in titanium alloys), is it used for predicting certain properties (such as the C-equivalent is used for weldability in C-steels), does it have to do with corrosion resistance, etc. etc. I would be grateful if anyone has background info on this topic.

### RE: Zinc in Brass / Bronze

(OP)
Ummmmm, thanks for the reply, but I had already seen the web page (and am familiar with various equivalents used in C-steels, Ti-alloys, cast irons, etc). I need more information than is readily available on the internet. Who was Guillet and why did he/she develop that formula? Is it for predicting whether the alloy will be alpha or alpha + beta (as is done with the Al and Mo equivalents in titanium alloys), is it used for predicting certain properties (such as the C-equivalent is used for weldability in C-steels), does it have to do with corrosion resistance, etc. etc. And why is it only valid for alloy content up to 1%? I would be grateful if anyone has background info on this topic.

### RE: Zinc in Brass / Bronze

Re: “Is it for predicting whether the alloy will be alpha or alpha + beta”
---Yes, that is purpose of  the rule.  It enables prediction of whether a multi-component alloy will be alpha or alpha + beta.  All the other alloying elements are converted via factors, added to the original zinc content, then the ‘zinc equivalent’ can be used with the Cu-Zn binary phase diagram to make the phase(s) prediction.

Re:  “is it used for predicting certain properties”
--- Yes, especially for physical properties such as strength (hardness).  The greater the alloying addition to a single phase alloy such as alpha, the greater the amount of solid solution (substitutional) strengthening.  Thus, its use for high tensile strength brass.

Re: “does it have to do with corrosion resistance”
--- Yes, a two-phase alloy such as alpha+beta will corrode far worse than single phase alpha.
Alpha and beta have different galvanic potentials, so in the presence of an electrolye (an ionic solution), the beta phase will preferentially corrode. Also, during high temperature oxidation, a single-phase oxide is more protective and can form far more easily over a single-phase alloy.

Re:  “And why is it only valid for alloy content up to 1%?”
--- The article mentions that it works for additions of up to 2% of each element, but of course that is general and will vary for each element, plus there can be an interaction effect.  You would need a book of ternary phase diagrams to find the actual limits for any one element ‘X’ added to the Cu-rich corner of the Cu-Zn-‘X’  phase diagram.  Hume-Rothery found that extensive solid solubility can occur if the diameters of the metal atoms differ by less than 15%.  So, if the diameter of ‘X’ differs by more than 15% from the Cu atom, the limit will be less.

E. Guillet studied steels as well as brass, and came up with diagrams for predicting phases in Mn-containing steels; his plot shows %Mn vs. %C, and his plot for Ni-containing steels shows %Ni vs. %C. The latter diagram can be seen in the following article:
http://www.key-to-steel.com/Articles/Art10.htm

If you are interested in the dealloying (e.g., dezincification) mechanism, see
Stratmann, M. and Rohwerder, M., Nature v. 410, 420–423 (2001)
Erlebacher, J. et al. Nature, v. 410, 450–453 (2001).
These papers refer back to
Tammann, G. Z. Anorg. Allg. Chem., v. 107, 1–239 (1919).
Masing, G. Z. Anorg. Allg. Chem., v. 118, 293–308 (1921).
but don’t mention E. Gaudillet:

“…two concepts: the 'parting limit' and the 'critical potential'. The parting limit has a long history, dating back to work by Tammann in 1919.  According to Tammann, dealloying occurs if the less inert component exceeds a specific concentration limit, the parting limit.  Seeking an explanation for this threshold, Masing calculated the probability with which a continuous filament of active (less inert) atoms would dissolve in a randomly orientated alloy in solution.  As expected, this probability depends strongly on the concentration of the active atoms.”—from Stratmann and Rohwerder (2001).

### RE: Zinc in Brass / Bronze

Re E. Guillet.
--- It seems he/she practised metallurgy a considerable time ago, perhaps ca. 1915-1945.  In the Guillet-microstructural diagrams for Mn-steels and Ni-steels, the lines intersect the x-axis at 1.65 wt.% C, which, according to the reference below, was thought to be the austenite composition of the L = austenite + Fe3C eutectic when Guillet constructed these diagrams.  The presently accepted value is 2.06 wt.% C.

Physical Metallurgy for Engineers, M. Tisza, ASM Int., Materials Park, Ohio (2001).

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