Effect of deformation induced precipitation on dynamic aging process and improvement of mechanical/corrosion properties AA7055 aluminum alloy

An improved low-temperature thermo-mechanical treatment (LTMT based on DYA: dynamic aging) aiming to discover the action of deformation-induced precipitation to microstructures and corrosion resistance was proposed that included a conventional T6 peak aging (120 °C/24 h) and a subsequent dynamic aging. Its influence on mechanical properties, electrochemical behavior and intergranular/exfoliation corrosion resistance of 7055 Al alloy were investigated by tensile testing, polarization curve, intergranular/exfoliation corrosion testing combined with optical microscope and transmission electron microscope observation. It shows that after the conventional T6 peak aging, the matrix precipitates were fine and dispersive while the grain boundary precipitates were coarse and continuously distributed. With the introduction of dynamic aging, the grain boundary precipitates become discontinuously distributed gradually without much coarsening of matrix precipitates. As a result, the LTMT process can improve intergranular/exfoliation corrosion resistances without sacrificing strength that could be attributed to the discontinuous grain boundary precipitates and fine dispersed matrix precipitates, respectively. The improved corrosion resistance was also confirmed by polarization curves and conductivity test. It indicates that the present LTMT process may be a good alternative to produce heat-treatable Al alloy sheets with good strength and corrosion resistance.