Dear Nidhi Chaubey

In general, it is expected that the Vickers hardness of a material will increase after cold rolling, as the cold working process introduces dislocations and increases the density of defects in the material. However, in the case of a material that has undergone alligatoring or other forms of severe deformation, the situation can be more complicated.

Alligatoring is a type of severe deformation that results in a wavy or zig-zag pattern on the surface of the material. This type of deformation can cause significant damage to the microstructure of the material, leading to a reduction in its mechanical properties. In the case of an Al alloy that has undergone alligatoring, it is possible that the material has suffered from cracking or other forms of damage that have reduced its Vickers hardness.

Additionally, the alligatoring process can result in changes to the texture and grain structure of the material, which can also affect its mechanical properties. Depending on the severity of the alligatoring and the specific properties of the alloy, it is possible that the Vickers hardness of the material could decrease after this type of severe deformation.

In summary, while it is generally expected that the Vickers hardness of a material will increase after cold rolling, the alligatoring defect can introduce significant damage and changes to the microstructure of the material, which can result in a reduction in its mechanical properties, including Vickers hardness.

Thank you so much sir for this helpful answer,I was also thinking the same that might be decreasing due to the rolling defect.

It is generally true that cold rolling of metal alloys leads to an increase in hardness due to the deformation and strengthening of the material. However, the appearance of alligatoring defects during cold rolling can significantly affect the mechanical properties of the material, including the hardness.

Alligatoring is a type of surface defect that can occur during cold rolling when there is a significant difference in thickness between the center and edges of the rolled sheet. This can cause the edges of the sheet to become overworked and damaged, leading to cracking and fracturing in a pattern that resembles the scales of an alligator.

The appearance of alligatoring defects can significantly reduce the strength and hardness of the material by creating areas of local deformation and damage. The extent of this effect will depend on the severity of the alligatoring and the specific alloy being used.

Therefore, it is possible that the Vickers hardness of the Al alloy could be lower after cold rolling with alligatoring defects than it was in the as-received condition. However, it is important to note that other factors, such as the grain structure, temperature, and strain rate, can also affect the hardness of the material. It would be necessary to perform further analysis, such as microstructural characterization or tensile testing, to fully understand the mechanical behavior of the Al alloy after cold rolling with alligatoring defects.