Brief Description of the Equipment/Machine:

A rolling machine is needed to roll aluminum to different strain. Furthermore, a tensile testing machine is required to obtain tensile properties of rolled aluminum.

Theory

Work hardening is the phenomenon whereby a ductile metal becomes harder and stronger as it is plastically deformed. Sometimes it is also called strain hardening, or, because the temperature at which deformation takes place is “cold” relative to the absolute melting temperature of the metal, cold working. Generally, cold working is carried out below recrystallization temperature. The strain-hardening phenomenon is explained on the basis of dislocation-dislocation strain field interactions. The dislocation density in a metal increase with deformation or cold work due to dislocation multiplication or the formation of new dislocations. Consequently, the average distance of separation between dislocations decreases. On average, dislocation-dislocation strain interactions are repulsive. The net result is that the motion of dislocation is hindered by the presence of other dislocations. As the dislocation density increases, this resistance to dislocation motion by other dislocations becomes more pronounced. Therefore, the applied stress (tensile and yield) required to deform a metal increases and ductility decreases with increasing cold work.

Fig. 1 shows the engineering stress – engineering strain curves of the aluminum at different magnitude (%) of rolling. The following can be observed: (a) Young’s modulus remains same, (b) yield strength increases from 0 % (as received) to 60 %, (c) ultimate tensile strength (UTS) increases from 0 % to 60 %, and (d) strain to failure decreases from 0 % to 60 %. The table below summarizes the properties. Fig. 2 shows the effect of cold rolling on tensile strength and ductility of different materials.




Table 1:Mechanical properties for different % of rolling