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Abstract: A pointless conversion film was prepared using 6063 aluminum alloy as the substrate in a conversion slag composed of fluorosilicate and ammonium fluoride. The effect of conversion solution composition and process conditions on the corrosion resistance of the fluorosilicate conversion film was studied based on the uncorroded area fraction of the sample after 168 hours of salt spray test. The optimized process parameters for fluorosilicate conversion were Na2SiF63-5 g/L, NH4F 5-7 g/L, pH 5.5-6.5, and temperature 25-35. C. During the conversion process, a dense chromium free conversion film composed of F, Al, Na, O, and Si was obtained on the surface of the aluminum alloy after being treated with fluorosilicate for 12-16 minutes. The self corrosion potential of the aluminum alloy significantly shifted forward, and the corrosion resistance was improved. Keywords: aluminum alloy; Fluorosilicate: conversion membrane; Durability Chinese Library Classification Number: TQ153.6 Literature Identification Code A Article number: 1004-227X (2012) 05-0037-04 Preface China is a major country in the production and use of aluminum alloys, which are widely used in industries such as aerospace, automotive electronics, machinery and food. Due to the standard electrode potential of aluminum alloy being -1.67 V and its active chemical properties, corrosion can occur under acidic or alkaline conditions, affecting the normal use of aluminum alloy. Therefore, industrial applications often require anti-corrosion treatment of aluminum alloys. Commonly used treatment techniques include anodizing, micro arc oxidation, chemical conversion, and coating techniques [1-3]. Due to the economic and effective advantages of chromate conversion, it has been widely used for a long time. However, due to the carcinogenic toxicity of hexavalent chromium, countries and regions have successively legislated to prohibit the use of chromate metal surface treatment technology. Currently, trivalent chromium conversion technology is widely used as a transitional technology to replace chromate conversion. However, trivalent chromium is still toxic and there is a risk of oxidation to hexavalent chromium. Therefore, it is urgent to study new environmentally friendly chromium free chemical conversion treatment technologies with good anti-corrosion performance and stable process operation. Shi Tie et al. [4-7] have conducted research on rare earth conversion coatings on the surface of aluminum alloys and achieved positive results, but the process stability still needs to be improved. Wang Cheng et al. [8-9] studied the passivation effect of molybdate and manganese salt on aluminum titanium, but the corrosion resistance of molybdate conversion film and the stability of manganese salt need to be strengthened. M. A, Smit et al. [11-13] added organic compounds to treat aluminum alloys in fluorotitanic acid or fluorozirconic acid to obtain a conversion film with good corrosion resistance. However, this technology requires high pre-treatment requirements for aluminum alloys and is only applicable to ordinary aluminum alloys. N.N. Voevodin et al. of the US Air Force Materials Preparation Research Institute [14] prepared SiO2 coating with good corrosion resistance on 2024 aluminum alloy surface by sol-gel method. There are very few studies and reports on chemical conversion membranes of fluorosilicates in China. This article conducts a preliminary study on the film formation of fluorosilicates. 2 Experiments 2.1 Experimental Materials Using 3.5cmxl.5cmxO.1cm 6063 aluminum sheet as the matrix, its main components (mass fraction) are: Si 0.20%~0.60%, Fe 0.35%, Cu O.10%
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