Research Of The Multifunctional Ceramic Coatings On The Surface Of Aluminum Alloys

Aluminum alloys are widely used in aerospace, automobile, electronics andshipbuilding industries, for they possess high specific strength, low density and excellentprocessing performance. In spite of this, with rapid development of industry fields, there isan increasing need for high quality aluminum products with preferable surface properties.Metal-based inorganic ceramic coatings, combining high temperature resistance, goodwear resistance and adequate corrosion resistance, has been successfully applied on thesurface of steels. However, until now the research of ceramic coatings on the surface ofaluminum alloys is still limted, so further study is indispensable and essential.In the present work, the ZL104alloy was selected as the based alloy, the preparationporcess and compositions of the multifunctional ceramic coatings on were alsosystematically studied. The main component of the base-coating-slurry is listed as follow:ceramic powder （SiO₂, Al₂O₃, Cr₂O₃, Al etal）, silicon-chromium composite, additives（Na₂SiO₃, Na₂SO₄, CaO etal） and composite add materials （FeO and Cu₂O）. SiO₂possesses high wear resisitance and corrosion resistance and its melting point is low; as ahigh-intensity phase, Al₂O₃has crystal lattice effect with the oxide film on substratesurface; as a high abrasion phase, Cr₂O₃has the function of corrosion inhibition; as acommon binder, Si-Cr composite sol could also improve the sintering activity after a largeamount of nanoscale particles were introducted. The volume expansion of themiddle-price-oxide, FeO and Cu₂O and Al powde after heat treatment could offset thevolume shrinkage of the ceramic coating during sintering process, so that the coatingachieved densification.The preparation progress about ceramic coating is: with water as the carrier liquid,composite sol as a binder, add a variety of metal inorganic oxide, mix and mill them fullyto get dispersed ceramic slurry, then coat it on the surface of ZL104alloy, after sintered ata certain temperature, a layer of inorganic ceramic coating with a certain thichness waspreparaed. With the means of scanning electron microscopy （SEM）, energy dispersivespectrometer （EDS）, X-ray diffraction （XRD）, the structure and morphology of the coating were analyzed, the mechanism was also explored. The best pretreatment process andpreparation process was found via comparing different sample’performance. The bestpretreatment process is: surface leveling�'ultrasonically cleaned in acetone�'Boilingwater bath processing. The preparation process is: coating�'dry film at roomtemperature�'heated at520℃with a heating rate of10℃/s�'With furnace cooling.The study found that when FeO content is under5%（wt%）, coating with goodsintering properties, good compactness, high hardness, thermal shock resistance, wearresistance and good water resistance can be preparaed. New phases like Fe₂O₃、Fe₂SiO₄、（Cr,Fe）2O₃、Al₂SiO₅etal. generated at the interface and coating inside shows that theintroduction of FeO into coating can promote the solid phase sintering among differentceramic particles and at the interface between substrate and coating， which can improvethe coating strength and interface binding. However， with the addition of FeO increasing,coating becomes porous, water resistance decreasing, composition reunion and and theemergence of low hardness particles during the sintering process also make the wearresistance, the surface hardness and thermalshock resistance and other performance of thecoating decrease, so FeO content should be controlled below5%（wt%）.The study also found that when the Cu₂O content is20%to25%（wt%） can thecoating get the optimal performance. New phases like CuO、CuSiO₃、CuCrO₂、CuAlO₂、Al₂SiO₅etal. generated at the interface and coating inside shows that the introduction ofCu₂O into coating can promote the solid phase sintering among different ceramic particlesand at the interface between substrate and coating， which can improve the coatingstrength and interface binding. While the Cu₂O content is more than25%, someperformances of the coating like water resistance, compactness, wear resistance, surfacehardness and thermal shock resistance decline. So the Cu₂O content should be controlledbetween20%to25%. To further enhance the performance of the coating, sealing study ofthe ceramic coating shows that, after sealed by polytetrafluoroethylene （PTFE）, smoothcoating with good hydrophobic, anti-moisture absorption, self-lubrication and otheradvantages can be acquired.A layer of dense inorganic ceramic coating on the surface of the aluminum alloy substrate can be achieved by low-temperature sintering, it has good combination withmatrix, good performance, thus, shows a very broad prospects of development in practicalapplications.