Copper alloys can be wrought or cast. Being ductile, they can be cold- or hot- rolled easily relative to other conventional non-ferrous alloy systems. Depending on the manufacturing technique and the treatment they are subjected to, one can extract several important inferences from microstructural characterization. In brass and bronze alloys for example, deformation from extruding results in extensive formation of ‘twins’ in the microstructure. The picture below shows how twins reveal themselves in a rolled brass alloy. Care has to be taken to not induce any deformation while preparing the sample.

Depending on the treatment parameters the alloy is subjected to, such as annealing temperature, grains can recrystallize or grow. When the temperature distribution in the part is not uniform, the grains sizes can vary. The same phenomenon can occur from extrusion or rolling loads. Considering that copper alloys deform easily, the grain size variation can play a critical role in deciding the mechanical properties of the final part.

Copper alloy microstructures can contain a wide range of phases represented by greek alphabets. The presence of a particular phase depends on the alloy system and the fabrication method. Among the various phases, α-phase can be considered principal as it indicates the FCC (Face centered cubic)-structure of copper at equilibrium. When all the alloying elements are dissolved in the copper matrix, which is usually the case in Cu-Ni systems, one observes a single phase of α. However, adding elements can promote formation of other phases giving rise to polyphase microstructures. For example, raising the composition of tin above 11% in cast tin-bronzes can result in polyphase microstructures with islands of δ-phase (a tin-rich FCC-structured phase). Shown below is a polyphase microstructure of a cast bronze alloy.

Intermetallic precipitates as seen in the microstructure above, in the intergranular regions, can be disastrous for structural applications. For certain applications, the precipitates are advantageous designed to refine grain sizes. Whichever the case, metallography gives critical cues in the morphology and characteristics of such precipitates.

One principal factor affecting the conductive properties of pure copper is the amount of oxygen it contains. Oxygen can also profoundly change the microstructure of the alloy. It is interesting to note that, copper and oxygen form a eutectic system like the Cu-Al alloy systems.