Why might heat treatment be required for certain aircraft repairs?

Heat treatment is often necessary for certain aircraft repairs primarily to restore the material properties of the metal. When metals are subjected to processes like welding or have sustained damage, their internal structure can change, leading to modifications in their mechanical properties such as strength and ductility. Heat treatment processes can help redistribute the stresses within the metal, relieve residual stresses created during welding, and facilitate the reestablishment of a molecular structure that enhances desired mechanical characteristics.

By applying heat treatment, materials can regain necessary attributes that ensure they are capable of withstanding the forces and stresses encountered during flight operations. This is critical in maintaining the overall structural integrity and safety of the aircraft. Maintaining properties like ductility allows the metal to deform without fracturing, which is vital in high-stress aviation environments. Other options, while they may relate to the broader context of aircraft maintenance, do not accurately capture the essential role of heat treatment in restoring material strength and ductility after repair processes.