In the present work, an innovative iron-based aluminium anodizing process was studied. The concept was born form the necessity to find an alternative to the Duralti process developed by Gruppo Gaser, an italian company specialized in the surface treatments of metals. The peculiarity of this process lies in the embedding of titanium dioxide into the aluminium oxide coating through the addition of potassium titanium oxalate in the bath, giving outstanding hardness, corrosion resistance and photo-catalytic properties. However, its high operating cost and poor aestethical appearance limit the commercial appeal of the treatment. Therefore, this thesis aims to develop an alternative process by replacing potassium titanium oxalate with a similar compound based on iron i.e., ammonium iron oxalate (AIO), in order to provide comparable mechanical properties and, at the same time, introducing the possibility of color customization. As a matter of fact, AIO is largely used as a dyeing agent in a post-anodizing treatment. Instead, in this case the coloring was performed during the anodizing process, saving time. In addition, AIO is cheaper respect to the titanium compound used in the Duralti process, leading to a significative cost reduction. The research has been organized in phases: firstly, the impact of each reagent present in the bath was investigated. Then, a similar evaluation was done by assessing the effects on the mechanical and microstructural properties of the main process parameters, namely temperature, voltage, anodizing time and electrolyte concentration. To demonstrate the competitiveness of the new treatment, a comparison with the Duralti process was performed, mainly in terms of hardness and oxide microstructure. This detailed phase of study has paved the way for the preindustrialization of the iron-based process, in which different sets of parameters were tested according to their performances. The obtained results were particularly interesting, showing an hardness in the order of 450-500 HV, very similar to the one obtained with the Duralti process. Moreover, comparable results were obtained in terms of corrosion resistance, roughness and respect of the geometric tolerances.
Nel presente lavoro, è stato studiato un innovativo trattamento di anodizzazione dell'alluminio basato sul ferro. L'idea è nata dalla necessità di trovare un'alternativa al processo Duralti sviluppato da Gruppo Gaser, un'azienda italiana specializzata nei trattamenti superficiali dei metalli. La peculiarità di questo trattamento risiede nella presenza di biossido di titanio all'interno dello strato di ossido di alluminio, ottenuta mediante l'aggiunta di potassio titanio ossalato nel bagno, donando eccellente durezza, resistenza a corrosione e proprietà fotocatalitiche. Tuttavia, gli alti costi operativi e lo scarso aspetto estetico ne limitano l'appetibilità commerciale. Pertanto, questa tesi si pone l'obiettivo di sviluppare un processo alternativo sostitutendo il potassio titanio ossalato con un composto simile basato sul ferro, ovvero l'ammonio ferro ossalato (AFO), in modo da garantire proprietà meccaniche comparabili e allo stesso tempo introducendo la possibilità di modificare la colorazione. Inoltre, l'AFO è più economico rispetto al composto di titanio usato nel processo Duralti, portando ad un significativo abbattimento dei costi. La sperimentazione è stata organizzata in fasi: in primo luogo, è stato valutato l'impatto di ogni singolo reagente presente nell'elettrolita. Successivamente, una valutazione simile è stata fatta riguardo agli effetti su proprietà meccaniche e microstruttura dei principali parametri di processo, ovvero temperatura, voltaggio, tempo di anodizzazione e concentrazione dell'elettrolita. Per dimostrare la competitività del nuovo trattamento, è stato eseguito un confronto con il processo Duralti, principalmente in termini di durezza e microstruttura dell'ossido. Questa dettagliata fase di studio ha fatto da apripista alla preindustrializzazione del processo basato sul ferro, nel quale differenti set di parametri, scelti in base alle loro prestazioni, sono stati testati. I risultati ottenuti sono stati particolarmente incoraggianti, mostrando una durezza nell'ordine dei 450-500 HV, molto simile a quella ottenuta dal processo Duralti. Inoltre, risultati simili sono stati ottenuti in termini di resistenza a corrosione, rugosità e rispetto delle tolleranze geometriche.
Development of an innovative anodizing process based on oxalate compounds
Ibrahim, Federico
2019/2020
Abstract
In the present work, an innovative iron-based aluminium anodizing process was studied. The concept was born form the necessity to find an alternative to the Duralti process developed by Gruppo Gaser, an italian company specialized in the surface treatments of metals. The peculiarity of this process lies in the embedding of titanium dioxide into the aluminium oxide coating through the addition of potassium titanium oxalate in the bath, giving outstanding hardness, corrosion resistance and photo-catalytic properties. However, its high operating cost and poor aestethical appearance limit the commercial appeal of the treatment. Therefore, this thesis aims to develop an alternative process by replacing potassium titanium oxalate with a similar compound based on iron i.e., ammonium iron oxalate (AIO), in order to provide comparable mechanical properties and, at the same time, introducing the possibility of color customization. As a matter of fact, AIO is largely used as a dyeing agent in a post-anodizing treatment. Instead, in this case the coloring was performed during the anodizing process, saving time. In addition, AIO is cheaper respect to the titanium compound used in the Duralti process, leading to a significative cost reduction. The research has been organized in phases: firstly, the impact of each reagent present in the bath was investigated. Then, a similar evaluation was done by assessing the effects on the mechanical and microstructural properties of the main process parameters, namely temperature, voltage, anodizing time and electrolyte concentration. To demonstrate the competitiveness of the new treatment, a comparison with the Duralti process was performed, mainly in terms of hardness and oxide microstructure. This detailed phase of study has paved the way for the preindustrialization of the iron-based process, in which different sets of parameters were tested according to their performances. The obtained results were particularly interesting, showing an hardness in the order of 450-500 HV, very similar to the one obtained with the Duralti process. Moreover, comparable results were obtained in terms of corrosion resistance, roughness and respect of the geometric tolerances.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/175596