Why electrical resistivity of metals alloys increases with degree of cold working?

Resistance is due to scattering of conduction electrons. A metallic crystal can be viewed simplistically as a periodic array of ions with a cloud of delocalised conduction elections. The electrons do not scatter of the ions themselves because the crystal is periodic. There are two significant causes of scattering: 1. scattering off vibrations of the atomic lattice (phonons). This contribution to the resistivity is proportional to temperature. 2. scattering off defects in the crystal. At low temperature, this is the cause of a finite 'residual resistivity'. The two terms add linearly Rtotal = R1(T) + R2 Cold working a metal will introduce defects and thus lead to an increase in R2. Conversely, annealling the metal at high temperature will remove defects and reduce the residual resistivity.