The Effect of Ag Addition on the Corrosion of Zn-22wt%Al Alloys
- PDF / 521,919 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 83 Downloads / 174 Views
Z3.4.1
The Effect of Ag addition on the corrosion of Zn-22wt%Al Alloys 1 2 2 2 Flores M. *, Huerta L.2, Casolco S. R. , Muhl S. , Torres-Villaseñor G. , and Luna J.A.1
1. Departamento de Ingeniería de Proyectos, CUCEI, Univ. de Guadalajara, A. P. 307, Zapopan, Jal., 45101, México. 2. Instituto de Investigaciones en Materiales, UNAM, A. P. 70-360, México D.F., 04510, México. * E-mail: [email protected]
ABSTRACT A new Zn–Al-Ag alloy (ZINAG) with mechanical superplastic properties has been developed. In this work four of the Zn–22wt%Al eutectoid alloy doped with between 0.5 to 4.24 wt% Ag have been studied. The superplastic behavior can be explained as a consequence of the fine grain distribution induced during the deformation process. Here the corrosion resistance of these alloys was studied by means of potentiodynamic polarization and measurements of the temporal evolution of the corrosion potential, in a 0.5 M NaCl solution. The corrosion products in the sample surface were analyzed by Rutherford Backscattering Spectrometry (RBS), X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). It was found that the corroded surface had lost more Zn than Al. The surface was examined by SEM and it was seen that the corrosion products adhered to the surface cracks. It was found that the alloy with 2.12 wt% concentration of Ag had the best corrosion resistance in the electrolyte used, but no clear tendency with the Ag concentration was found. INTRODUCTION The Zn-22wt%Al-2wt%Cu alloy called Zinalco is a superplastic material previously developed by one of the authors and whose superplastic behavior and deformation mechanisms have been extensively studied [1-2]. In Zinalco the mechanical and physical properties of the superplastic eutectoid Zn-Al alloy were enhanced by the addition of copper [3,4]. In this study an evaluation has been made of the influence of the substitution of the copper by silver on the corrosion resistance in a saline solution, the mechanical properties will be reported elsewhere. Previously, the corrosion of Zn-22wt%Al-2wt%Cu in a 0.5M NaCl solution was studied and it was reported that the corrosion potential was –1050 mV after 60mins of immersion in the electrolyte. [5]. Since Ag is a more noble metal than Cu it might be expected that Zn–Al-Ag (Zinag) alloy would have a similar or more noble corrosion potential than Zinalco. This work is the first report on the corrosion resistance studies of the Zn-Al alloys and the analysis of the corrosion products in the surface. EXPERIMENT AND METHODS The specimens were prepared by melting 99.9% pure Al, special high grade Zn and 99.95% pure Ag in a graphite crucible in air and casting into 24 mm thick ingots. The casting was warm rolled at 350ºC to a thickness cubic of 10 mm. After testing, selected specimens were mechanically polished and examined by SEM. Two groups of samples were used for this study: one was used for the electrochemical corrosion and corrosion products analysis and other for the analysis of the natural atmospheric oxida
Data Loading...
