Effect of second-phase particles evolution and lattice transformations while ultrafine graining and annealing on the corrosion resistance and electrical conductivity of Al-Mn-Si alloy

Al-Mn-Si specimens were subjected to constrained groove pressing, cold-rolling and annealing, respectively. Microstructure characterizations indicated that second-phase particles were arranged along the material flow direction and did not orient at grain boundaries. Analysis of x-ray diffraction patterns exhibited that severe straining led to dynamic restoration and lattice swelling. Since findings for annealed specimens did not follow a linear trend; however, they were in good agreement with corrosion characteristics and electrical conductivity results. Outputs of electrochemical polarization test revealed that corrosion rate has direct correlation with lattice distortion and dislocation density measurements. As most of the particles have not remarkable open circuit potential with aluminum matrix along with other existent particles and also did not contain required size to act as origin of pitting corrosion, they would capable of forming the passive layer porous and subsequently could prevent encouraging uniform passive layer. In the case, they let the aggressive ions to penetrate beneath the passive layer and react with talented sites like dislocations and grain boundaries. Scrutiny of lattice d-spacing proved that by imposing deformation, electrical conductivity alters by change in d-spacing since by annealing at elevated temperature conductivity follows the winner of competition between d-spacing, lattice distortion and particles transformations.