Galvanized steels with different thicknesses of coatings were exposed to the wet-dry cycles in the presence of NaCl. The degradation of galvanized steels was investigated at different exposure times by electrochemical impedance spectroscopy. Further, the degradation is categorized into four characteristic stages, including tau(1): dissolution of zinc, tau(2): galvanic protection by metallic zinc, tau(3): barrier protection by zinc corrosion products, and tau(4): onset of the underlying steel corrosion, respectively. The underlying steel was protected by the zinc corrosion products for a relatively long time even after the metallic zinc coating was completely corroded (i.e., the tau(3) stage).

过去20年，国际上成功商业化了热浸镀锌铝镁镀层。该镀层以Zn、Al、Mg三元合金为主，按Al含量的范围，可分成“低铝”、“中铝”、“高铝”3大类。因锌铝镁镀层具有高平面耐蚀性和高切口耐蚀性的特点，在建筑业和家电业得到了广泛的应用。同时锌铝镁镀层还具有摩擦因数低且稳定、以及镀层冲压磨损量少等特性，因此近年来在汽车工业的应用也正在逐渐拓展。简要回顾了锌铝镁镀层的发展历程，重点围绕镀层成分、组织、性能、应用等方面进行了介绍，并探讨了锌铝镁镀层未来发展趋势。

In situ time-lapse optical microscopy was used to examine the microstructural corrosion mechanisms in three zinc-magnesium-aluminium (ZMA) alloy coated steels immersed in 1% NaCl pH 7. Preferential corrosion of MgZn(2) lamellae within the eutectic phases was observed in all the ZMA alloys followed by subsequent dissolution of Zn rich phases. The total extent and rate of corrosion, measured using time-lapse image analysis and scanning vibrating electrode technique (SVET) estimated mass loss, decreased as Mg and Al alloying additions were increased up to a level of 3 wt% Mg and 3.7 wt% Al. This was probably due to the increased presence of MgO and Al(2)O(3) at the alloy surface retarding the kinetics of cathodic oxygen reduction. The addition of 1 × 10(-2) mol dm(-3) Na(3)PO(4) to 1% NaCl pH 7 had a dramatic influence on the corrosion mechanism for a ZMA with passivation of anodic sites through phosphate precipitation observed using time-lapse image analysis. Intriguing rapid precipitation of filamentous phosphate was also observed and it is postulated that these filaments nucleate and grow due to super saturation effects. Polarisation experiments showed that the addition of 1 × 10(-2) mol dm(-3) Na(3)PO(4) to the 1% NaCl electrolyte promoted an anodic shift of 50 mV in open circuit potential for the ZMA alloy with a reduction in anodic current of 2.5 orders of magnitude suggesting that it was acting primarily as an anodic inhibitor supporting the inferences from the time-lapse investigations. These phosphate additions resulted in a 98% reduction in estimated mass loss as measured by SVET demonstrating the effectiveness of phosphate inhibitors for this alloy system.

Along with the increasing pace of marine resource development and strategic deployment of China, the infrastructure materials and deployed aircraft were facing severe salt fog corrosion during the construction process of the South China Sea. Materials damage in this environment is much more serious than that in other marine atmospheric environment. Owing to its location near the equator and the direct impact of solar radiation, Nansha marine atmosphere is a representative and typical climate with high temperature, high humidity, high salinity and high radiation. However, there has been lack of material corrosion data and relevant fundamental research until now. Carbon steel is usually one of the most widely used infrastructure materials and reference materials, and its corrosion data exposed to Nansha Islands marine atmosphere is much more important. These corrosion data can not only provide important basis for environmental corrosivity category, but also provide reference for indoor accelerated corrosion test. Therefore, in order to obtain useful information on selected construction materials, adopting the appropriate corrosion protection methods, and predicting the life of metallic structures under service, the exposure test was conducted on carbon steel Q235 and weathering steel Q450NQR1 in Nansha Islands for 2 and 5 months. Thickness loss analysis, macroscopic observation, SEM, XRD, optical profiler and tensile tests were conducted to study the initial corrosion behavior on both sides of Q235 and Q450NQR1 in Nansha marine atmosphere. The results showed that the initial corrosion behavior of both steels at this site was more serious than those at most areas, such as Wanning and Xisha Islands, and the corrosion of skyward of both steels was more serious than that of field-ward. The rust layer formed on field-ward was easier to fall off. After exposure for 2 months, the thickness loss of Q235 was the same as that of Q450NQR1, and corrosion products on both sides were mainly composed of γ-FeOOH, α-FeOOH and Fe3O4; while after 5 months' exposure, the thickness loss of Q235 was much larger than that of Q450NQR1, and corrosion products were mainly composed of γ-FeOOH, α-FeOOH, Fe3O4 and β-FeOOH. The relative composition of β-FeOOH and γ-FeOOH was fewer on the field-ward, and the relative composition of Fe3O4 was fewer on the skyward.

采用腐蚀失重法、宏观形貌观察法、SEM、XRD、白光干涉及拉伸实验等分析手段对碳钢Q235和耐候钢Q450NQR1在南沙大气环境下的初期腐蚀行为进行了研究。结果表明，Q235和Q450NQR1在南沙大气环境中的初期腐蚀比万宁及西沙等海洋大气环境中的腐蚀严重，2种钢的朝天面都比朝地面腐蚀严重，朝地面的锈层更容易脱落。暴晒2个月时，Q235和Q450NQR1的腐蚀失厚相近。暴晒5个月时，Q235的腐蚀失厚明显高于Q450NQR1的腐蚀失厚。2种钢在暴晒2个月时，朝天面和朝地面的腐蚀产物都主要为γ-FeOOH、α-FeOOH和Fe₃O₄；而暴晒5个月时，朝天面产物中出现了β-FeOOH，而朝地面β-FeOOH极少。朝天面的产物中Fe₃O₄相对含量少于朝地面，γ-FeOOH的相对含量多于朝地面。

Many countries have begun to focus on the development and utilization of marine resources, involving ports, docks, oil production platforms, cross-sea bridges, large ships, and other marine engineering facilities, since beginning of the 21st century. Marine atmospheric corrosion issues encountered during construction put the safety of these marine engineering facilities in jeopardy. The Nansha Islands, which are located in the southernmost part of the South China Sea, are in a typical tropical marine atmosphere environment with no long-term corrosion data. The steel used in marine engineering is the premise of expanding marine space and exploiting marine resources, as well as the guarantee of enhancing marine national defense strength and safeguarding maritime rights and interests. Because of its poor corrosion resistance, the service life has certain limitations. As a result, studying the corrosion mechanism of carbon steel in this typical atmospheric environment after long-term exposure is crucial for engineers. The corrosion behavior of low carbon steel Q235 and weathering steel Q450NQR1 was investigated using the corrosion loss method, macroscopic morphology observation, SEM, XRD, and electrochemical and tensile tests after 34 months of exposure in the Nansha atmospheric environment. The results show that the corrosion dynamic of the two sheets of steel in the marine atmosphere of Nansha Islands can be divided into two stages. The corrosion rate of the second stage is smaller than that of the first stage. Weathering steel Q450NQR1 has demonstrated better corrosion resistance in a short exposure time. The rust layer on the skyward and field-ward sides of mild steel Q235 is thicker than that of weathering steel Q450NQR1 after 21 and 34 months of exposure, and there are more cracks in the rust layer, which could promote oxygen and chloridion diffusion to the substrate and speed up the corrosion process. The main components of corrosion products are γ-FeOOH, α-FeOOH, β-FeOOH, and Fe3O4, the relative contents of each product were different with the extension of exposure time. Furthermore, corrosion on the field-ward sides of the two steel sheets was worse than corrosion on the skyward sides. This is because the rust layer on the field-ward side was easily removed, resulting in a weakened resistance to corrosive medium. With the extension of exposure time, the thickness of the rust layer on the skyward side of carbon steel Q235 and weathering steel Q450NQR1 is increasing, and the tensile strength was gradually reduced. That is, Q235 and Q450NQR1 are more likely to fail owing to the thickening of the rust layer during use resulting in safety accidents.

采用腐蚀失重法、宏观形貌观察法、SEM、XRD、电化学及拉伸实验等分析手段对Q235和Q450NQR1在南沙大气环境中暴晒21和34个月后的腐蚀行为进行研究。结果表明，2种钢在南沙海洋大气环境中腐蚀动力学过程分为2个阶段，第二阶段腐蚀速率较第一阶段小。耐候钢Q450NQR1在短期内就已体现出更好的耐蚀性。暴晒21和34个月后，Q235朝天面和朝地面的锈层均比Q450NQR1的厚，且锈层中的裂纹更多，利于O₂和Cl^-向基体扩散，加速腐蚀过程。2种碳钢朝天面和朝地面锈层的主要成分组成为γ-FeOOH、α-FeOOH、β-FeOOH和Fe₃O₄，各产物的相对含量随着暴晒时间的延长都有一定的差异。此外，2种钢的朝地面均比朝天面的腐蚀严重，这是由于朝地面的锈层极易脱落，使其对腐蚀介质的阻碍作用减弱。随着暴晒时间的延长，碳钢Q235和耐候钢Q450NQR1表面锈层不断增加，抗拉强度逐渐降低。即在使用过程中随着锈层的增厚，Q235和Q450NQR1钢越容易失效，引发安全事故。