This Thesis was carried out at Leonardo Helicopters at Cascina Costa plant. The aim of this work was to carry out the experimental activity needed for the characterization of a REACH compliant chemical conversion treatment of Aluminium alloys (hereinafter called as “Process B”) alternative to the chromate conversion treatment (CCC) (“Process A”) currently used in Leonardo Helicopters. Aluminium alloys are widely used in aerospace applications thanks to their low weight and high mechanical properties combined with a low cost. To increase corrosion resistance of aluminium alloys and to improve paint adhesion, different surface treatments are used; among them, chromate conversion treatment is one of the most adopted. It is based on Chromium trioxide (Cr(VI)) that has been classified as Substance of Very High Concern (SVHC) by the article 57 of REACH regulation. This substance is currently included in the Annex XIV of REACH regulation (“Authorization List”) and a sunset date has been established. Process B is a new generation conversion treatment based on Cr (III), Zr and rare earth element followed by a passivation to increase the corrosion resistance of the coating. For both processes, A and B, two application methods were used to prepare the samples to be tested: immersion and brush-on. Leonardo Helicopters defines qualification requirements in accordance with internal and military specifications (MIL-DTL-81706 and MIL-DTL-5541). Therefore, the following properties of Process B were studied in comparison with Process A: corrosion resistance (as treated and painted samples), paint adhesion with two primers, electrical resistance, coating weight, axial fatigue behaviour. The pre-treatments of Process B applied by brush-on were optimized after the failure of corrosion test carried out on the first set of samples. SEM analyses were carried out on as-treated samples to study the surface morphology of both processes. The first results obtained by means of this characterisation make Process B a promising alternative to the current CCC.
Questo lavoro di tesi è stato svolto presso lo stabilimento Leonardo Elicotteri di Cascina Costa. Lo scopo del lavoro è quello di svolgere le attività sperimentali necessarie alla caratterizzazione di un processo di conversione chimica dell’Alluminio REACH compliant (chiamato Processo B) alternativo alla conversione di cromatazione (CCC) (Processo A) attualmente utilizzata da Leonardo Elicotteri. Le leghe di Alluminio trovano ampio utilizzo in applicazioni aerospaziali grazie a un basso peso ed elevate proprietà meccaniche combinate ad un basso costo. Per aumentarne la resistenza a corrosione e l’adesione delle vernici, sono utilizzati diversi trattamenti superficiali; uno dei più diffusi è la conversione di cromatazione. Essa è basata sul triossido di cromo, classificato come SVHC (Substance of Very High Concern) dall’articolo 57 della normativa REACH. Questa sostanza è attualmente inserita nell’Annex XIV della normativa REACH (“Authorization list”) ed è stata stabilita una sunset date. Il Processo B è un processo di conversione di nuova generazione basato su Cr(III), Zr e terre rare seguito da una passivazione volta a incrementare la resistenza a corrosione del rivestimento. Per entrambi i processi, A e B, due metodi di applicazione sono stati utilizzati per preparare i provini: a immersione e a pennello. Leonardo Elicotteri definisce i requisiti di qualifica in accordo a specifiche interne e militari (MIL-DTL-81706 e MIL-DTL-5541). Di conseguenza, le seguenti proprietà del Processo B sono state studiate per confronto con il Processo A: resistenza a corrosione (provini solo con il trattamento di conversione e provini verniciati), adesione di due primer di verniciatura, resistenza elettrica, coating weight, comportamento a fatica assiale. Il pretrattamento del Processo B applicato a pennello è stato ottimizzato in seguito al fallimento dei test di corrosione svolti sul primo set di provini. Analisi al SEM sono state eseguite su provini con il solo rivestimento per studiare la morfologia di entrambi i processi. I primi risultati ottenuti da questo lavoro indicano il Processo B come una promettente alternativa al processo CCC attualmente utilizzato.
REACH compliant Cr(III) based conversion coating of aluminium alloys for aerospace applications. A two step process for the replacement of Cr(VI) based conversion coating
CAIELLI, MARCO
2016/2017
Abstract
This Thesis was carried out at Leonardo Helicopters at Cascina Costa plant. The aim of this work was to carry out the experimental activity needed for the characterization of a REACH compliant chemical conversion treatment of Aluminium alloys (hereinafter called as “Process B”) alternative to the chromate conversion treatment (CCC) (“Process A”) currently used in Leonardo Helicopters. Aluminium alloys are widely used in aerospace applications thanks to their low weight and high mechanical properties combined with a low cost. To increase corrosion resistance of aluminium alloys and to improve paint adhesion, different surface treatments are used; among them, chromate conversion treatment is one of the most adopted. It is based on Chromium trioxide (Cr(VI)) that has been classified as Substance of Very High Concern (SVHC) by the article 57 of REACH regulation. This substance is currently included in the Annex XIV of REACH regulation (“Authorization List”) and a sunset date has been established. Process B is a new generation conversion treatment based on Cr (III), Zr and rare earth element followed by a passivation to increase the corrosion resistance of the coating. For both processes, A and B, two application methods were used to prepare the samples to be tested: immersion and brush-on. Leonardo Helicopters defines qualification requirements in accordance with internal and military specifications (MIL-DTL-81706 and MIL-DTL-5541). Therefore, the following properties of Process B were studied in comparison with Process A: corrosion resistance (as treated and painted samples), paint adhesion with two primers, electrical resistance, coating weight, axial fatigue behaviour. The pre-treatments of Process B applied by brush-on were optimized after the failure of corrosion test carried out on the first set of samples. SEM analyses were carried out on as-treated samples to study the surface morphology of both processes. The first results obtained by means of this characterisation make Process B a promising alternative to the current CCC.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/139566