Influência de parâmetros de processo sobre a morfologia de camadas de fosfato e desempenho de aços fosfatizados e pintados

• Ano de defesa: 2005
• Autor(a) principal: Cynthia Helena Soares Boucas
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Engenharia Metalúrgica e de Minas; Engenharia metalúrgica; Engenharia de minas; Ciência dos materiais
• Link de acesso: http://hdl.handle.net/1843/BUOS-8DWG47

The influence of process parameters on phosphate coating morphology and corrosion performance of phosphated and painted samples is presented in this work through study of the relationship among process parameters, structure, properties and corrosion performance. The process parameters evaluated were phosphating methodology andconcentration of refiner bath. The coating morphology was evaluated concerning its structural properties: phase, coating mass and crystal size and also its porosity. The performance of phosphated and painted materials was evaluated by corrosion tests. The results showed with regard to process parameters, the phosphating methodology influences the phase formation, crystal size, coating mass and the porosity. The carbon steel phosphated by immersion process produced a structure more rich of phosphophyllite phase than hopeite one, which resulted in formation of cubic crystals. On the other hand, the carbon steel phosphated by spray process produced preferentially hopeite phase and galvanized steel produced exclusively that phase, which resulted in formation of platelet type crystals. Crystal size was fine and mass coating was low for materials processed by spray. For this reason, materials processed by spray presented more porosity and corrosion. The morphology of phosphate coatings was influenced besides by concentration of refiner bath with regard to size crystal, mass and coatingporosity. It was observed that the crystal size increased with reduction of concentration of refiner. Coating mass presented different behaviors for carbon steel and galvanized steels. In the case of carbon steel, coating mass decreased with reduction of concentration of refiner. On the other hand, the coating mass of galvanized steels increased with the reduction of concentration of refiner, presenting values above usual ones in the condition without refining. These variations affected porosity and corrosion resistance of phosphated and painted materials. The coating porosity increased with reduction of concentration of the refiner for carbon steel, hot-dip galvanized and galvannealed steel. For the electrogalvanized steel, porosity changed a little with the concentration of the refiner. In spite of that, the increasing of corrosion with increasingcoating porosity was maintained. Therefore, the coating porosity also plays an important role specially on performance of phosphated and painted materials.