Effect of Magnesium Content on the Corrosion Behaviors of Gr f /Al Composite
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DUCTION
RECENTLY, great attention has been paid to graphite-fiber-reinforced aluminum composites (Grf/ Al) because of their high specific strength, high specific modulus, low density, and excellent wear performance.[1] The microstructure and mechanical properties of Grf/Al composites have been widely studied.[2,3] It is well known that the extensive reactant Al4C3 at the C/Al interface is unfavorable to strength.[4] Several methods have been developed to inhibit the deleterious interface reaction, such as alloying, fiber surface modification through passive oxidation,[5] metallic or ceramic coating on fibers,[6] and optimization of process parameters, and among these methods, alloying seems to be a promising way because of its convenience. In our previous study, the addition of magnesium in an Al matrix alloy would decrease the C/Al reaction and improve the mechanical properties of the Grf/Al composite.[7] However, the effect of magnesium content on the corrosion behaviors of the Grf/Al composite has not been reported. In the present study, corrosion behaviors of the Grf/Al composite with different magnesium contents (from 0 to 8.5 wt pct) were studied by potentiodynamic polarization measurements, immersion tests, and electrochemical impedance spectroscopy (EIS) analysis. The corrosion morphology was analyzed by scanning electron microscopy (SEM), and its effect on magnesium was discussed. XU WANG and QIANG GUO, PhD Students, GUOQIN CHEN, Lecturer, WENSHU YANG, Master’s Student, GAOHUI WU and DAMING JIANG, Professors, are with the School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China. Contact e-mail: wx1979875@ hotmail.com Manuscript submitted May 10, 2010. Article published online October 22, 2010 3458—VOLUME 41A, DECEMBER 2010
II.
EXPERIMENTAL
The Grf/Al composites were fabricated with the pressure infiltration method, and the chemical compositions of the matrix of four composites are given in Table I. The weight loss of different composites samples was evaluated by immersion testing in 3.5 wt pct NaCl solution at room temperature. The specimens were weighed by a BP211D analytic balance (Sartorius AG, Go¨ttingen, Germany) with an accuracy of 1 9 105 g. The electrochemical measurements were performed in a flat cell. The diameter of the exposure area of the sample was 10 mm. An Ag/AgCl electrode was employed as the reference electrode. The potential of this electrode with respect to the standard hydrogen electrode is +0.197 V; the auxiliary electrode was graphite. Potentiodynamic polarization measurements were performed in 3.5 wt pct NaCl solution in atmospheric air. EIS measurements were performed by applying a sinusoidal potential perturbation of 10 mV. The impedance spectra was measured with a frequency sweep from 100 kHz to 10 MHz in a logarithmic increment. All electrochemical experiments were performed after stabilization of the free corrosion potential at room temperature.
III.
RESULTS AND DISCUSSION
Figure 1 shows the potentiodynamic curves of four
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