| AVS 65th International Symposium & Exhibition | |
| Advanced Surface Engineering Division | Tuesday Sessions |
| Session SE-TuP |
| Session: | Advanced Surface Engineering Division Poster Session |
| Presenter: | James Fitz-Gerald, University of Virginia |
| Authors: | M.A. Melia, Sandia National Laboratories L. Agnew, University of Virginia J.M. Skelton, University of Virginia J.R. Scully, University of Virginia J.M. Fitz-Gerald, University of Virginia |
| Correspondent: | Click to Email |
The widespread implementation of lightweight magnesium alloys to the automotive and aerospace industries is currently limited by its poor and unpredictable corrosion response. Of major concern is the localized corrosion of Mg alloys, driven by a uniform population of electrochemically noble secondary phases present in the chemically heterogeneous microstructure, resulting in a rapid loss of structural integrity. These microstructural heterogeneities are accentuated when Mg alloys are welded causing galvanic coupling between weld zones. A research investigation to mitigate localized corrosion of a Mg alloy (AZ31B), with and without weldments, via laser surface engineering has been conducted. Lasers operating in a nanosecond pulse duration regime are capable of melting and solidification rates on the order of 109 K/s with the ability to extend the solid solubility limit of the alloying elements. The irradiation of AZ31B with an excimer laser (FWHM= 25ns, λ= 248nm) observed significant changes in the near surface microstructure and secondary phase particle dissolution, characterized in this case by scanning electron microscopy equipped with a backscatter electron detector. The corrosion response of Mg alloy AZ31B (3wt% Al, 1wt% Zn, 0.6wt% Mn, and Mg balance) was investigated using the accelerated atmospheric test (GMW14872) for 30 wet-dry cycles. The atmospheric exposure test consists of a 24-hour cycle involving three 8-hour stages. During the first stage, samples are held at ambient temperature and humidity (25 °C, 45% RH) and are sprayed every 90 minutes with a salt solution (0.9% NaCl, 0.1% CaCl2, 0.075% NaHCO3). During the second stage the temperature is increased to 49 °C and samples are continuously sprayed with a deionized water fog (~100% RH). During the third stage temperature is increased to 60 °C and held at less than 30% relative humidity. The corrosion product was analyzed using Fourier transform infrared spectroscopy (FTIR) and grazing incident x-ray diffraction (GI-XRD). At early stages of the exposure experiments the laser processed specimens showed less corrosion product coverage than as-polished or welded specimens.