Aluminum And Its Alloys Electrochemical Ceramic Processing Research

This paper investigated the surface reinforcement of aluminum and its alloys systematically using electrochemical deposition ceramic film(EDCF) technology in mixed organic carboxylic acid solutions. The properties, contents appearances and structures of the obtained films were examined by HVS-1000 sclerometer- 7503 vortex flow thicknessmeter EDS XRD and SEM etc. The process and mechanism of EDCF were also discussed. Additionally, the equipments and process of medium-sized test of EDCF technology were also tentatively studied in this paper.In mixed carboxylic acid solutions, smooth lustrous and yellow coffee violet-black etc analogous ceramic films could be deposited on L3 aluminum using EDCF technology under following conditions: film-formation complexing solvent 7.5-30g/L,film-formation additive 1.25-2.25 g/L, Na2W04 0.5-3.0g/L, peak current density 6-15A/dm2,weak agitation. The obtained films show a thickness of 10-60u m, a micro-hardness of 400-600HV and excellent stability in acid and alkaline. In the mixed electrolytes that organic carboxylic acid acts as main salts, and some activator were added, a smooth homogeneous and gray or yellow analogous ceramic films could be obtained on ZL108 and LY12 aluminum. The analogous ceramic films show a thickness of 15-40um, a micro-hardness of 300-510HV The best film-formation condition is that: organic acid 3-15g/L, film-formation additive 2-4.0g/L, Na2WO4 0.75-3.5g/L, activator 0.2-1.0g/L, peak current density 10-18A/dm2, pulse frequency 3-5Hz, circuit through/break ratio l:3-4,time 8-9min,weak agitation, T 30-40.The EDS results show that the content elements of the cast aluminum films are 0, Al, P, S, C and Si. XRD investigation shows that the films of cast aluminum and hard aluminum were both non-crystal films. The aluminum oxides hydroxides and their hydrates are the main composition phases together with some organic or inorganic elements that are P S C and some complicated compounds that formed by Si and P S C. The surface SEM characteristics of the cast aluminum and hard aluminum films show that the films are coacervated and deposited by number of circular pellets with the diameter of 0.1-0.3 u m. Further SEM study of cross section shows that the film consists of a double-layer structure. The outer loose layer is about 10 u m, the inner compact layer is 20-25 U m and connects with the substrate tightly by themicro-irregular of the substrate. There are many groove micro-cracks in the compact layer.Electrochemical and SEM studies show that the process of cast aluminum analogous ceramic film formation could be divided into four stages, namely initial anodization and deposition stage, rapid growth stage, slow growth stage and deposition-dissolution dynamic equilibrium stage. The growth of the analogous film mainly occured in the second stage with a growth rate of 8 u m/min. The cast aluminum no-crystal analogous ceramic film with special structures and properties formed in weak acid mixed electrolytes can be explained by a film growth mechanism that includes the following steps under the surface chemical electrochemical and Joule-heat interactions: (a) formation and accumulation of anion polymer particles in the interface of cast aluminum and electrolytes, (b) deposition and enrichment of these particles on the anode, (c) high-temperature dehydration and rapid refrigeration in the deposition layer.Additionally the equipment and process parameters such as pretreatmenU contents of electrolytes, concentration peak current density reaction time etc. in the medium-sized test of EDCF technology are tentatively investigated. The problems arised during the test and the resolving measure are also discussed.