Study On The Effect Of Heat Treatment And Pre-deformation On Localized Corrosion Behavior Of AA2099 Al-Li Alloy

The new type aluminum-lithium(Al-Li)alloys are increasingly used in the aerospace industry,due to their low density,high strength and good processability,significantly improving the pay load and fuel effiency of the aircrafts.While,the Al-Li alloys are susceptible to localized corrosion in moist or salt-fog environment because of the adding of Li element.So far,researches on corrosion resistance of the new type Al-Li alloys are few.In this work,based on the AA2099 Al-Li alloy produced by Aloca and CHINALCO,the effect of heat treatment and pre-deformation on localized corrosion behavior of the alloy was studied though immersion testing,potential dynamical/ potentionstatic and scanning electron microscopy(SEM).The following conclusions have been drawn from the researches.1)For the Alcoa alloy,grains of solution heat treated(SHT),T3,T6 and T8 specimen are elongated along the extrusion direction.Microhardness and corrosion potentials of the specimen in order are 128.5GPa,146.3GPa,155.5GPa,188 GPa and-0.648 V,-0.653 V,-0.7V,-0.736 V respectively.The tendency of micohardness change is consisted with that of corrosion potentials,indicating that aging significant influenced the corrosion potentials of the alloy.After potential dynamical polarization,the morphology of localized corrosion of SHT and T3 samples are typical crystallographic corrosion;T6 and T8 samples are characterized by preferential corrosion of grain boundaries and grains.2)The variation of microstructure,hardness and corrosion behavior of SHT,T3,T6 and T8 specimen of the CHINALCO are similar those of the Alcoa alloy with same temper,but the microstructure of the alloy is more heterogeneous,and grains are coarser.Some grains of T8 speciman contain slipbands,with their orientation with respect to the extrusion direction being 48°,56°,66° and 77°respectively.The morphology of localized corrosions of the T8 speciman show parallel corrosion volume,this indicating that the localized corrosion in T8 sample is related to the slipbands.3)3%?6% and 9% cold stretching have little impacts on corrosion behavior of the SHT sample of the CHINALCO,microhardnesses of the stretched specimen are in average of 120 GPa,and the open circuit potentials are in average of –0.6V,the corrosion morphology of the specimen show crystallographic corrosion.4)After different time(4h,24 h,96h)of aging treatment,the microhardness of SHT sample increaes first and then decreases,the maximum microhardness is 162 GPa of(24 hours);corrosion tendancy increases in turns,open circuit potentials are-0.67 V,-0.70 V and-0.73 V respectively;discrepancy of corrosion behavior is obvious,surface denudation of(4 hours),grain boundaries and grains corrosion of(24 hours),severe alveolate grains corrosion of(96 hours).5)After different time(4h,24 h,96h)of aging treatment,the microhardness of 3% sample increases first and then decreases,the maximum microhardness is 176GPa;corrosion tendancy increased in turns,open circuit potentials are-0.68 V,-0.72 V and-0.735 V respectively;discrepancy of corrosion behavior is obvious,grain boundaries and grains corrosion of(4 hours),severe alveolate grains corrosion of(24 and 96 hours).