TY - JOUR
T1 - Film breakdown and nano-porous Mg(OH)2 formation from corrosion of magnesium alloys in salt solutions
AU - Brady, M. P.
AU - Rother, G.
AU - Anovitz, L. M.
AU - Littrell, K. C.
AU - Unocic, K. A.
AU - Elsentriecy, H. H.
AU - Song, G. L.
AU - Thomson, J. K.
AU - Gallego, N. C.
AU - Davis, B.
N1 - Publisher Copyright:
© The Author(s) 2015. Published by ECS.
PY - 2015
Y1 - 2015
N2 - Small angle neutron scattering (SANS) and scanning transmission electron microscopy (STEM) were used to study film formation by magnesium alloys AZ31B (Mg-3Al-1Zn base) and ZE10A (Elektron 717, E717: Mg-1Zn + Nd, Zr) in H2O and D2O with and without 1 or 5 wt% NaCl. No SANS scattering changes were observed after 24 h D2O or H2O exposures compared with as-received (unreacted) alloy, consistent with relatively dense MgO-base film formation. However, exposure to 5 wt% NaCl resulted in accelerated corrosion, with resultant SANS scattering changes detected. The SANS data indicated both particle and rough surface (internal and external) scattering, but with no preferential size features. The films formed in 5 wt% NaCl consisted of a thin, inner MgO-base layer, and a nano-porous and filamentous Mg(OH)2 outer region tens of microns thick. Chlorine was detected extending to the inner MgO-base film region, with segregation of select alloying elements also observed in the inner MgO, but not the outer Mg(OH)2. Modeling of the SANS data suggested that the outer Mg(OH)2 films had very high surface areas, consistent with loss of film protectiveness. Implications for the NaCl corrosion mechanism, and the potential utility of SANS for Mg corrosion, are discussed.
AB - Small angle neutron scattering (SANS) and scanning transmission electron microscopy (STEM) were used to study film formation by magnesium alloys AZ31B (Mg-3Al-1Zn base) and ZE10A (Elektron 717, E717: Mg-1Zn + Nd, Zr) in H2O and D2O with and without 1 or 5 wt% NaCl. No SANS scattering changes were observed after 24 h D2O or H2O exposures compared with as-received (unreacted) alloy, consistent with relatively dense MgO-base film formation. However, exposure to 5 wt% NaCl resulted in accelerated corrosion, with resultant SANS scattering changes detected. The SANS data indicated both particle and rough surface (internal and external) scattering, but with no preferential size features. The films formed in 5 wt% NaCl consisted of a thin, inner MgO-base layer, and a nano-porous and filamentous Mg(OH)2 outer region tens of microns thick. Chlorine was detected extending to the inner MgO-base film region, with segregation of select alloying elements also observed in the inner MgO, but not the outer Mg(OH)2. Modeling of the SANS data suggested that the outer Mg(OH)2 films had very high surface areas, consistent with loss of film protectiveness. Implications for the NaCl corrosion mechanism, and the potential utility of SANS for Mg corrosion, are discussed.
UR - http://www.scopus.com/inward/record.url?scp=84923343627&partnerID=8YFLogxK
U2 - 10.1149/2.0171504jes
DO - 10.1149/2.0171504jes
M3 - Article
AN - SCOPUS:84923343627
SN - 0013-4651
VL - 162
SP - C140-C149
JO - Journal of the Electrochemical Society
JF - Journal of the Electrochemical Society
IS - 4
ER -