PVD法에 의한 Zn-Mg 合金 薄膜의 製作과 電氣化學的 耐蝕特性

Abstract

The Zn coatings have been well known as the most suitable surface modification for the corrosion protection metal. Recently, however, severe corrosive environments issue came with great attention, hence, development of better corrosion resistant Zn coating method became to be required. That is, the Zn coatings have occasionally some limitations which restrict its use in certain applications. Although undamaged Zn coating on steel gives a good corrosion resistance, the protection is not so good because the corrosion can occur at an accelerated rate if the coatings are scratched or otherwise damaged. Thus coatings offering a better galvanic or sacrificial protection for steel are desirable than offering by pure Zn. To this end, Zn-Mg alloy coating films were studied.

In this study, the Zn and Mg alloy thin films were prepared onto the cold-rolled steel(SPCC) substrates by vacuum evaporation and ion plating method. Moreover, the influence of gas pressures and substrate bias voltage, on composition ratio, morphology and crystal orientation of the Zn-Mg alloy thin films were investigated by energy dispersive X-ray spectroscopy(EDX), scanning electron microscopy(SEM) and X-ray diffraction(XRD), respectively. From the experimental results, (100-x)ZnㆍxMg alloy films are prepared onto cold-rolled steel substrates

where x ranged from 0 to about 38 atomic%. The alloy films show microcrystalline and grain structures respectively in accordance with preparation conditions such as composition ratio of Zn and Mg or gas pressures etc.. And X-ray diffraction analysis indicates not only the presence of the Zn-Mg thin films with forced solid solution but also the one of MgZn2 alloy films partly.

In addition the influence of Mg in the alloy film, morphology and crystal orientation of the Zn-Mg alloy films on corrosion behavior is evaluated by electro-chemical anodic polarization tests in deaerated 3% NaCl solution. From the measured results, all the prepared Zn-Mg alloy films obviously showed good corrosion resistance compared with 99.99% Zn and 99.99% Mg ingots for evaporation metal. It is, therefore, thought that Mg element in the Zn-Mg films, produces smaller and denser grain structure so that they may improve the formation of homogeneous passive layer in corrosion environment.