The Study Of Heat Treatment Processing And The Mechanism Of Corrosion For3003Aluminum Alloy Cathode Foil

The influence of heat treatment process, including intermediate annealing and aging on the specific capacitance of3003aluminum alloy foil for cathode was investigated by DSC, hardness,electrical resistivity,specific capacitance measurements,XRD, OM,SEM and TEM analyses. The interaction mechanism of precipitation and recrystallization and its effect on microstructures was studied. The cohesive energies, Fermi energies and local density of states (LDOS) were calculated by the first-principles based on pseudopotential plane wave method in this paper to investigate the physical nature of corrosion of3003aluminum alloy, mechanism of electrochemical corrosion was analyzed according to the calculated electronic structure parameter. The results are as follows:(1) On annealing at360℃and480℃,a lot of precipitates occur. For the precipitation prior to recrystallization at360℃,the grains become coarse,and the precipitates are nucleated preferentially in lattice defects, such as dislocations and sub-boundaries,so the precipitation process is affected by the presence of lattice defects,i.e. higher cold reduction results in larger amount of precipitates. However,for the recrystallization at480℃prior to precipitation,the precipitation is independent of cold rolling reduction,and fine grains are obtained.(2) When the foils are aged at80℃for3h, it will increase the volume fraction of fine and dispersed Al6Mn intermetallic particles, as well as the distribution hommogeneity of dislocation,the specific capacitance of cathode foil is increased to580μF/cm.When the foils are aged at160℃,the volume fraction of coarsened intermetallic (Fe,Mn)Al6particles is increased and leading to poor corrosion property with heterogeneous etched pits, which is not conducive to the improvement of specific capacitance.(3) The stable phase in3003aluminum alloy is Al2Cu<Al6Mn<Mg2Si<ALPHA. The Fermi energy(Ef) values of these phases with Ef<(Mg2Si)<Et{Al6Mn)<Et<(ALPHA)<E,(Al2Cu) indicate that ALPHA is most likely to lose electrons while Mg2Si is difficult. LDOS result reveals that Al6Mn and ALPHA phases are unstable compared with Mg2Si in the same external conditions, they are more likely to lose electrons and easier to corrod. The difference in Fermi energy between different phases in3003aluminum alloy forms the elctrodynamic force of the electrochemical corrosion, which leads electrons to flow from the Al with higher Fermi energy to second phases with lower Fermi energy,further to corrode in3003aluminum alloy.