| AVS 62nd International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF-ThP |
| Session: | Thin Films Poster Session |
| Presenter: | Michael Melia, University of Virginia |
| Authors: | M.A. Melia, University of Virginia N. Birbilis, Monash University, Australia J.R. Scully, University of Virginia J.M. Fitz-Gerald, University of Virginia |
| Correspondent: | Click to Email |
The development of Mg alloys has been accelerated over the last decade due to the need for significant weight reduction of structural components. One long-standing obstacle regarding the use of Mg alloys for widespread field application is their intrinsically poor corrosion resistance and lack of surface films or oxides. Micro-galvanic induced “self-corrosion” due to alloy heterogeneity is a key concern. Therefore, chemical and structural homogenization is of long standing and great interest. Furthermore, there is a need to exploit possible benefits of low fluence LSM, local composition variations and LSM processing gas environments on corrosion behavior. Here we report on the effect of laser surface modification (LSM) on the corrosion resistance of an Mg alloy (AZ31B-H24).
Samples were processed with a pulsed excimer laser operating at 248 nm and a fluence = 1.5 J/cm2. Microstructure and composition were characterized with scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD), and energy dispersive spectroscopy (EDS). Corrosion analysis was performed in a standard three electrode corrosion cell in quiescent 0.6 M NaCl solution. Electrochemical Impedance Spectroscopy (EIS) and potentiodynamic polarization measurements were used to determine corrosion resistance, anodic/cathodic behavior, pitting potential and open circuit potential (OCP). Corrosion experiments were imaged by optical video microscopy during testing to draw conclusions regarding the breakdown of the irradiated surface.
Layered structures of nanoscale MgO, Mg3N2, andAlN constituents formed in the irradiated region as a function of process gas and proximity to the Al8Mn5 intermetallic particles (IMPs). Partial homogenization of IMPs was observed, reducing the initial particle size by 40-60% and creating large areas of Al/Mn enrichment, irrespective of process gas used (Ar, N2). The results show that a reduction in the H2 evolution reaction rate was achieved correlated with an order of magnitude decrease in the cathodic current density, as well as a 100 mV to 200 mV reduction in the open circuit potential over short immersion times of up to 4 hours, irrespective of processing gas. In addition, Impedance results support these findings with a 4 and 25 fold increase in the polarization resistance after processing in both N2 and Ar atmospheres respectively. The behavior in full immersion has not been extrapolated to long term field testing.
Acknowledgements
This material is based on research sponsored by the U.S. Army Research Laboratory and U.S. Air Force Academy under agreement number W911NF-14-2-0005 and FA7000-13-2-002, respectfully.