**2.1 Alloys and metal matrix composites preparation**

Zinc-Aluminum (ZA) alloys of different compositions were prepared from zinc (99.98 wt pct), aluminum (99.94 wt pct), and composites were prepared by adding SiC and Al2O3 particles to the alloys. The compositions of the alloys and composites prepared and directionally solidified are: Zn-27wt%Al, Zn-50wt%Al, Zn-27wt%Al + 8vol%SiC, Zn-27wt%Al + 15vol% SiC, Zn-50wt%Al + 8vol%SiC, Zn-50wt%Al + 15vol%SiC, Zn-27wt%Al + 8vol%Al2O3, Zn-27wt%Al + 15vol%Al2O3.

The chemical compositions of the commercially pure metals used to prepare the alloys are presented in Table 1. The molds were made from a 23 mm i.d. and 25 mm e.d. PYREX (Corning Glass Works, Corning, NY) tube, with a flat bottom, a cylindrical uniform section and a height of 200 mm. The sample was a cylinder 22 mm in diameter and 100 mm in height.

Corrosion Resistance of Directionally Solidified Casting Zinc-Aluminum Matrix 39

A conventional three-compartment glass electrochemical cell with its compartments separated by ceramic diaphragms was used. The test electrodes consisted of sections of the ZA ingots (see Figure 1) were positioned at the glass corrosion cell kit (leaving a rectangular area in contact with the electrolyte). The potential of the test electrode was measured against a saturated calomel reference electrode (0.242 V vs NHE), provided with a Luggin capillary

Voltammograms were run between preset cathodic (open circuit potential -1.500 V) and anodic (Es,a = -0.700 V) switching potentials at potential sweep rates (v), at 0.002 V.s-1. Impedance spectra were obtained in the frequency range of 10-3 Hz and 105 Hz at open

For comparison purposes, experiments using pure metals and aluminum-based alloys with different structures were conducted under the same experimental conditions. All the corrosion tests experiments were triplicate and the average values and graphical outputs are

Fig. 1. Experimental device for electrochemical tests. (f) A glass corrosion cell kit with a

platinum counter electrode and a sutured calomel reference electrode (SCE).

tip. The Pt sheet was used as a counter electrode.

circuit potential.

reported.


Table 1. Chemical composition of the Zn and Al used to prepare the alloys.
