Article

Influence of heat treatment and microstructure on the corrosion of magnesium alloy Mg-10Gd-3Y-0.4Zr

Journal of Applied Electrochemistry (Impact Factor: 2.15). 06/2008; 39(6):913-920. DOI: 10.1007/s10800-008-9739-4

ABSTRACT The corrosion of Mg alloy Mg-10Gd-3Y-0.4Zr, in the as-cast (F), solution treated (T4) and aged (T6) conditions, was investigated
in 5% NaCl solution by immersion tests and potentiodynamic polarization measurements. The as-cast (F) condition had the highest
corrosion rate due to micro-galvanic corrosion of the α-Mg matrix by the eutectic. Solution treatment led to the lowest corrosion
rate, attributed to the absence of any second phase and a relatively compact protective surface film. Ageing at 250°C increased
the corrosion rate with increasing ageing time to 193h attributed to increasing micro-galvanic corrosion acceleration of
the Mg matrix by increasing amounts of the precipitates. Ageing for longer periods caused a decrease in the corrosion rate
attributed to some barrier effect by a nearly continuous second-phase network. Electrochemical measurements did not give accurate
evaluation of the corrosion rate in agreement with the immersion tests.

1 Bookmark
 · 
211 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The bio-corrosion behaviour of Mg-3Zn-0.3Ca (wt.%) alloy in simulated body fluid (SBF) at 37°C has been investigated using immersion testing and electrochemical measurements. Heat treatment has been used to alter the grain size and secondary phase volume fraction; the effects of these on the bio-corrosion behaviour of the alloy were then determined. The as-cast sample has the highest bio-corrosion rate due to micro-galvanic corrosion between the eutectic product (Mg+Ca2Mg6Zn3) and the surrounding magnesium matrix. The bio-corrosion resistance of the alloy can be improved by heat treatment. The volume fraction of secondary phases and grain size are both key factors controlling the bio-corrosion rate of the alloy. The bio-corrosion rate increases with volume fraction of secondary phase. When this is lower than 0.8%, the dependence of bio-corrosion rate becomes noticeable: large grains corrode more quickly. Copyright © 2014 Elsevier B.V. All rights reserved.
    Materials Science and Engineering C 03/2015; 48:480-6. DOI:10.1016/j.msec.2014.12.049 · 2.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This review investigates the current application limitations of Mg and Mg alloys. The key issues hindering the application of biodegradable Mg alloys as implants are their fast degradation rate and biological consideration. We have discussed the effect of some selected alloying element additions on the properties of the Mg-based alloy, especially the nutrient elements in human (Zn, Mn, Ca, Sr). Different grain sizes, phase constituents and distributions consequently influence the mechanical properties of the Mg alloys. Solution strengthening and precipitation strengthening are enhanced by the addition of alloying elements, generally improving the mechanical properties. Besides, the hot working process can also improve the mechanical properties. Combination of different processing steps is suggested to be adopted in the fabrication of Mg-based alloys. Corrosion properties of these Mg-based alloys have been measured in vitro and in vivo. The degradation mechanism is also discussed in terms of corrosion types, rates, byproducts and response of the surrounding tissues. Moreover, the clinical response and requirements of degradable implants are presented, especially for the nutrient elements (Ca, Mn, Zn, Sr). This review provides information related to different Mg alloying elements and presents the promising candidates for an ideal implant.
    09/2013; 7(3). DOI:10.1007/s11706-013-0210-z
  • [Show abstract] [Hide abstract]
    ABSTRACT: Microstructure, mechanical and corrosion properties of four alloys, Mg–2Gd–2Zn, Mg–2Gd–6Zn, Mg–10Gd–2Zn and Mg–10Gd–6Zn (all are in weight percentages), prepared by gravity permanent mold casting were investigated. The results indicated that the intermetallic phases in the Mg–2Gd–2Zn alloy consisted mainly of (Mg, Zn)3Gd phase whereas the Mg–2Gd–6Zn alloy consisted of both I (Mg3Zn6Gd) and (Mg, Zn)3Gd phases. In addition, few Mg–Gd and Mg–Zn binary phases were also present in both the alloys. Lamellar long period stacking ordered (LPSO) phase was observed in alloys containing high concentrations of Gd (Mg–10Gd–2Zn and Mg–10Gd–6Zn alloys) in addition to the continuously distributed (Mg,Zn)3Gd phase along the interdendritic regions and grain boundaries. A small fraction of X phase (Mg12ZnGd) was also present in Mg–10Gd–2Zn alloy. Mg–10Gd–xZn alloys (x=2,6) exhibited higher yield strength due to the higher solute contents and the presence of LPSO phase in the matrix, but showed poor elongation due to the coarse continuous second phase at the boundary. Low Gd-containing alloys showed better elongation to failure and moderate strength due to the lower volume fraction of fine scale second phases. Corrosion resistances of the alloys decreased with increase in the total amount of alloying elements. Increase in Zn content from 2% to 6% in Mg–2Gd–xZn alloys did not alter the corrosion properties much; however, this increase in the high Gd-containing alloys had significant detrimental effects on the corrosion properties due to the significant increase in the volume of the second phases. In all the alloys, galvanic corrosion due to the second phase and filiform corrosion dominated the earlier stages of corrosion, and after long immersion times, the second phase, (Mg,Zn)3Gd, was found to become unstable and dissolved, leading to intergranular corrosion.
    Materials Science and Engineering A 02/2014; 595:224–234. DOI:10.1016/j.msea.2013.12.016 · 2.41 Impact Factor