Chromic acid (Cr⁶⁺) anodization process is widely used for the corrosion protection of aircraft aluminium alloys. Hexavalent chromium being toxic in nature need to be phased out by eco-friendly alternatives. In the present study modified tartaric-sulphuric acid (TSA) process has been developed followed by sealing in permanganate based bath to obtain 4 to 6 µm thick anodic oxide layer on 2024-T3, 6061-T6 and 7075-T6 aluminium alloys. The process was carried out using a pilot scale anodizing plant. The anodized specimens were characterized for visual observation, thickness, adhesion, electrical breakdown voltage, corrosion resistance and tensile behaviour. All the tests were carried out as per MIL-A-8625F specifications. The specimens were also subjected for about 800 hrs to real time corrosion testing, 200 metres away from sea shore at Mandapam Camp, Rameshwaram, India. The performance of the permanganate sealed TSA anodized aluminium alloys are comparable with that of the conventional chromic acid anodized coatings. This chromic acid-free anodization process has been qualified to airworthiness regulating standards by Indian military certification authorities. Efforts are in progress to commercialize this technology for use on aero platforms.

中文翻译：

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航空级铝合金无铬酸阳极氧化工艺的开发与认证

铬酸（Cr ⁶⁺) 阳极氧化工艺广泛用于飞机铝合金的腐蚀防护。六价铬本质上是有毒的，需要通过环保替代品逐步淘汰。在本研究中，已开发出改良的酒石酸-硫酸 (TSA) 工艺，然后在高锰酸盐基浴中密封，以在 2024-T3、6061-T6 和 7075-T6 铝合金上获得 4 至 6 µm 厚的阳极氧化层。该过程使用中试规模的阳极氧化设备进行。阳极氧化试样的特征在于目视观察、厚度、附着力、电击穿电压、耐腐蚀性和拉伸行为。所有测试均按照 MIL-A-8625F 规范进行。在距离拉梅什瓦拉姆曼达帕姆营地海岸 200 米的地方，样本还接受了大约 800 小时的实时腐蚀测试，印度。高锰酸盐密封 TSA 阳极氧化铝合金的性能与传统铬酸阳极氧化涂层的性能相当。这种无铬酸阳极氧化工艺已通过印度军事认证机构的适航监管标准认证。正在努力将该技术商业化以用于航空平台。