The effects of tellurium as the alloying element on the Al-Zn-In sacrificial anodes have been investigated in NaCl solution. Scanning electron microscopy, energy-dispersive x-ray analysis, and inductively coupled plasma mass-spectrometry have been employed to study the morphology and corrosion behavior of improved anodes. The corrosion of the Al-Zn-In-Te anode initiates at the segregations where Te is enriched. With the addition of Te as the alloying element, the Al-Zn-In anodes exhibit lower harmful impurity content, inhibition of self-corrosion, and higher current efficiency, which are desirable for sacrificial anodes.Aluminum alloy is used as sacrificial anodes because of its low electrode potential, high current capacity, and low weight. 1 It is well known that there are natural oxide films on the surface of pure Al. 2 Numerous investigations have improved properties of the oxide film by the anodizing process. [3][4][5][6][7][8][9] For activating the oxide film of Al, the elements have been added as alloying components such as Zn, In, Hg, Sn, Ga, Mg, The electrochemical activity of the oxide film was explained by taking into account the existence of highly conductive defective sites. 19 Especially, the Al-Zn-In anode was used in marine cathodic protection because of its excellent performance. 20,21 For better knowledge of the corrosion mechanism, some Al-Zn-In series anodes were surveyed, such as the Al-Zn-InMg-Ti-Mn alloy. 22 However, a study on Te as the alloying element of Al alloys is lacking. This paper describes the effects of Te on the electrochemical properties and the microstructure of Al-Zn-In alloy anodes. Al-Zn-In anodes are conspicuously improved by Te as the alloying element for excellent electrochemical properties as sacrificial anodes. Meanwhile, the Al-Zn-In-Sn-Te anode is investigated for better properties.
ExperimentalThe preparation of materials and electrodes.-The materials were prepared with pure Al ͑99.76%͒, high purity Zn ͑99.99%͒, In ͑99.999%͒, Sn ͑99.99%͒, and Te ͑99.99%͒. Nine species of alloys were used with nominal compositions Al-5Zn-0.015In ͑sample no. 1͒, Al-5Zn-0.015In-0.05Te ͑sample no. 2͒, Al-5Zn-0.015In-0.1Te ͑sample no. 3͒, Al-5Zn-0.015In-0.15Te ͑sample no. 4͒, Al-5Zn-0.015In-0.2Te ͑sample no. 5͒, Al-5Zn-0.015In-0.1Sn-0.05Te ͑sample no. 6͒, Al-5Zn-0.015In-0.1Sn-0.1Te ͑sample no. 7͒, Al5Zn-0.015In-0.1Sn-0.15Te ͑sample no. 8͒, and Al-5Zn-0.015In-0.1Sn-0.2Te ͑sample no. 9͒. The actual compositions of the alloys were determined by inductively coupled plasma-mass spectrometry ͑ICP-MS, Perkin-Elmer͒ analysis, as shown in Table I. The Al and Zn ingots were melted in a 1 kg capacity clay-graphite crucible in an electric resistance furnace. When the temperatures of the melt reached 760°C, the ingots containing other alloying elements were wrapped by the Al foil and were added into the melt with stirring and scumming. Finally, the molten metals were poured into a small cast iron cylindrical mold ͑⌽20 ϫ60 mm͒. Cylindrical rod electrodes were polished with 800 grade emery paper and 0...