METHODS OF REDUCING POROSITY IN BRASS

Introduction. Brass is an alloy of copper and zinc. It has been said that the measurable density of any pure metal(s), whose density(ies) are well-known, will always be less than their analytically computable densities--or their "true" densities (7:196). Why? A lack of maximal density, or some porosity, must exist in the metals' lattice structure or must be introduced in the alloying process. Explored here are methods metallurgists may use to minimize porosity in brass.

Brass. A useful alloy of two metals, copper and zinc (9:166), brass has been formed for cultural uses and ornamentation since the 13th century BC (1:9). The term, brass, indicates any of an infinite possible set of mixes of "copper-zinc alloys of varying composition" (9:166). The infinite variety results solely from the infinite possibilities for Zn-percentage in the alloy and the temperatures at which the alloy is formed, annealed, or quenched--matters largely of art.

About a half dozen general names are used to distinguish classes of brass, based virtually entirely on the percent of zinc present in the completed alloy. As one might expect, the ductility, hardness, and other physical properties of these brasses are variable as well. "Low-zinc brasses" as a very general category contain less than 20% zinc [and hence 80 or more percent copper (Cu)], and they happen to be "resistant to stress-corrosion" and are easily formed by hammering or other tool work (9:166

. . .
ons for metals and their alloys the Shakespearean realm: "Much Ado about Nothing, or Close to It" (7:192). He meant to imply that there may be as many as five types of--reasons for--porosity in metals, but they are difficult to distinguish, some even impossible to see (7:195-97). Metals are solids. The five types of "lack of density" (porosity) in cast or solidified metal are: Geometrical and interdendritic shrinkages, gas or "ghost" porosities, and lattice vacancies (7:197). Some are partially preventable, others are not. Geometrical shrinkage results in a (large) void in a casting whose (void) shape results from the shape of the mold and the cooling dynamics of that mold-geometry (7:197). Interdendritic shrinkage is porosity constituted of small, angular, internal voids, totally enclosed by dendrites , the void size and shape being related to the dendritic grain size and not to the mold's geometry (7:197). Gas porosity occurs as small (microscopically visible) rounded voids occurring within grains or at grain boundaries, resulting from previously present insoluble gas(es), now absent through agitation or escape or phase change (7:197). Ghost porosity is an "invisible" lack of density "tapering from the shrink cavity in ingots
. . .

Some common words found in the essay are:
Reduce Porosity, Powder Coating, Diagram Brasses, Introduction Brass, Ado Close, Zn Cu, Nagy Roy, Porosity Brass, Porosity Modern, Summary Conclusions, muntz metal, phase diagram, -phase solid, zinc brass, porosity brass, metals alloys, craddock ed occasional, craddock ed, occasional paper, cementation process, 50 2000 zinc, +l +, 2000 zinc brass, ed occasional paper, paper 50 2000,
Approximate Word count = 3599
Approximate Pages = 14 (250 words per page)