Effect of Build Orientation and Heat Treatment on Corrosion of Additively Manufactured Aluminum 6061 RAM2 With Boron and Titanium Additions

Additive manufacturing of high strength aluminum alloys is enabled by the addition of titanium and boron that react during manufacturing and help to rapidly stabilize the microstructure. In-situ reactions between aluminum, with the titanium and boron carbide additions, lead to the formation of boride, carbide, and aluminide precipitates that provide consistent printing and excellent mechanical performance but their impact on corrosion behavior is not yet established. In this study, the corrosion behavior of AA6061 RAM2, including effect of heat treatment and build orientation, was evaluated with immersion testing in neutral sodium chloride solutions under accelerated and non-accelerated corrosion conditions. Relative corrosion performance rankings were dependent on the testing methodology. AA6061 RAM2 exhibited more corrosion damage compared to wrought AA6061 in un-accelerated immersion conditions. However, electrochemical tests indicated that the RAM2 variants had better corrosion resistance than the wrought counterpart. Heat treated RAM2 samples were more susceptible to pitting than the as-built ones. However, build orientation and height did not have a measurable impact on corrosion behavior. The Ti and B4C additions had a minor effect on the anodic and cathodic polarization behavior which was dominated by the aluminum matrix phase. In contrast, at electrode potentials near the open circuit potential, pitting corrosion was driven by microgalvanic couple formation between the matrix and the aluminide, boride, and carbide precipitates, as well as the matrix and the unreacted/partially reacted Ti and B4C particles.