The production of galvanized steel with zinc (GI) presents great challenges due to the high demand for surface quality required for its applications. The automotive segment is one of the largest consumers of this type of product. In hot dip galvanizing lines, the main defect that affects the surface quality of the coatings is the dragging of dross particles. Some studies have already been carried out to understand the formation of these particles inside the zinc bath, however little is known about the trajectory of these particles in relation to the pot layout. In this study, two types of layout were simulated to assess how this interferes with the flow of zinc. In the results it was verified that, the position of the heating inductor significantly modifies the trajectory of the dross particles.
The production of hot-dip galvanized steel presents great challenges, because it is currently the main raw material in the manufacturing of automobiles, and its surface quality is fundamental for the construction of automobiles. Obtaining the best surface appearance in galvanized steels is directly related to understanding the phenomena involved in the galvanizing process. In this process, achieving thermal and chemical stability of the galvanizing pot means keeping topdross formation under control. The top-dross is the main problem to be controlled, because it impacts the surface quality of coated steel. Some studies have been conducted to understand the formation of top-dross particles into the zinc bath, but little is known about the path of the particles formed from the melting ingots. In this study, the trajectories of these particles were simulated. It has been found that, depending on the immersion depth, dross particles may have different destinations.
ResumoA crescente demanda por aços galvanizados com alta lubricidade tem impulsionado o desenvolvimento de pós-tratamentos que, aplicados sobre a superfície dos revestimentos, reduzem o atrito entre o ferramental e a chapa durante o processo de estampagem de peças críticas na indústria automotiva. Diante disso, a Usiminas desenvolveu, em parceria com a Quaker, a aplicação do pós-tratamento tipo microfosfato denominado Primecoat Z Auto, com a função de melhorar a estampabilidade de aços galvanizados a quente do tipo GI (Zn puro). Nesse estudo foi avaliada a Razão Limite de Estampagem (RLE) de um aço GI destinado a produção de peças críticas, após aplicação desse pós-tratamento em escala de laboratório. Adicionalmente, foram caracterizadas a morfologia e a constituição química do microfosfato, e o desempenho do aço quanto à fosfatização, à pintura automotiva e à resistência a corrosão. Concluiu-se que o filme de pós-tratamento é amorfo, constituído por Zn, P, Al e Mg, promovendo um excelente ganho de lubricidade ao aço GI, sem interferir nos processos subsequentes de fosfatização e de pintura nas montadoras. Além disso, o material apresentou excelente desempenho quanto à resistência à corrosão. Palavras-chave: Aço galvanizado; Estampabilidade; Pós-tratamento; Lubricidade. DEVELOPMENT OF HOT DIP GALVANIZED STEEL (GI) WITH APPLICATION OF POST-TREATMENT TO INCREASE LUBRICITY AbstractThe growing demand for galvanized steels with high lubricity has driven the development of post-treatments for reducing the friction between the stamping tools and the steel during the processing of critical parts in the automotive industry. Therefore, Usiminas has developed, in partnership with Quaker, the application of a micro-phosphate post-treatment called Primecoat Z Auto for improving the formability of hot dip galvanized steel GI (pure Zn). In this study the Limit Draw Ratio (LDR) of a GI steel for the production of critical parts, with application of this post-treatment in laboratory scale, was evaluated. It were also characterized the morphology and chemical composition of the micro-phosphate, and the performance of the steel as regards of phosphating, automotive paint and corrosion resistance. It was concluded the film of post-treatment is amorphous, consisted of Zn, P, Mg and Al, providing an excellent gain of lubricity for GI steel, without interfering in automaker's subsequent process of phosphating and painting. In addition, the material showed excellent performance in terms of corrosion resistance.
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