Microstructure of Alpha-brass

Copper alloys have been utilized in a variety of applications throughout history. They are of use environments requiring certain types of corrosion resistance. Alloying is necessary to achieve the desired mechanical properties.

The most common of these alloys are the brasses for which zinc, as a substitutional impurity, is the predominant alloying element. The alpha phase is stable for concentrations up to approximately 35 wt% Zn. This phase has an FCC crystal structure and is relatively ductile and easily cold- worked.

The following optical micrograph shows the microstructure of a sample of alpha brass. Careful surface preparations are necessary to reveal the details of the microstructure. The specimen must first be ground and polished to a smooth and mirrorlike finish. This is accomplished by using successively finer abrasive papers and powders.

The microstructure is fully revealed by a surface treatment with an appropriate chemical reagent in a procedure known as etching. The chemical reactivity of each of the grains depends on crystallographic orientation. As seen in the microstructure below etching characteristics then vary from grain to grain and incident light is reflected differently. This is responsible for the apparent differences in grain color.

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400x Magnification