Microstructure of two-phase metallic materials after deformation

Introduction

The microstructure of metal materials is important for the study of their mechanical properties, such as strength and hardness. The microstructure of metal materials is affected by various factors, such as alloying elements, heat treatment, and plastic deformation. In this experiment, the effects of different levels of plastic deformation on the microstructure of two metals are studied.

Experimental methods

Two kinds of metal materials were used in this experiment. One was the Cu-Al alloy with 3.2% aluminum and 0.2% cobalt. The other was the pure copper rod with a diameter of 3mm. Both materials were electropolished with PASO before carrying out the experiment.

The plate-like samples were cut from the rod materials using friction saw. The samples were put on the compression testing machine and compressed by different levels of deformation. The deformation was calculated as the ratio of the longitudinal extension to the original length of the sample. After that, the samples were quenched in a quench tank for 10 minutes, and then annealed for 20 minutes at a temperature of 600℃. All samples were crushed by a polishing machine and then the microstructures observed under a scanning electron microscope.

Results and discussion

Figure 1 shows the microstructure of the Cu-Al alloy after plastic deformation of 10%, 20% and 30%. The grains are much finer in the 10% deformation case than in the 20% and 30% cases. This is probably due to the fact that the plastic deformation at 10% caused the dislocation density to increase and the grains to break down. The grain boundary can also be seen clearly in Figure 1, which is the boundary between two grains and is associated with the stress present in the sample.

Figure 2 shows the microstructure of the pure copper rod after the same levels of deformation. As compared to the Cu-Al alloy, the grain size of the copper rod is much finer. This is likely due to the high resistance of copper to plastic deformation. As can be seen in Figure 2, the annealing process has recrystallized some of the grains and increased the average grain size.

Conclusion

In this experiment, different levels of plastic deformation were applied to two types of metal materials and the microstructures observed. The microstructure of the Cu-Al alloy showed a finer grain size after 10% deformation than that after 20% and 30% deformation. In contrast, the pure copper rod showed a finer grain size after deformation compared to the Cu-Al alloy. This is likely due to the high resistance of copper to plastic deformation. The annealing process also caused some recrystallization of the grains, which increased their average size.

After deformation of two metallic materials, microscopic organization was observed. The two materials are aluminum and copper.

Observations showed that the two materials had a slight change in microstructure compared to their initial stages. For aluminum, the microstructure was composed of primary grains, secondary grains and grain boundaries. Under the high magnification, an array of fine-grained particles was observed within the primary grains. The grain boundaries in aluminum were identified clearly.

In copper, an irregular and sparse array of particles was observed. The grain boundaries in copper were more prominent than aluminum as well. Moreover, copper seemed to have a more jagged microstructure.

Deformation of the two materials had caused a serious refinement and uniformity in the microstructures. The grain boundaries were more defined and some of the loose particles and impurities had been removed.

On the whole, deformation of both materials was successful in inducing important changes in the microstructure. The microstructures became more uniform and refined and the grain boundaries were more defined in both materials. This indicates that these two materials can be used for a range of applications, especially for ones with high strength.