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INTEROGATION OF THE MANUFACTURING ROUTE OF ALUMINIUM AA 1050 USED IN LITHOGRAPHIC APPLICATION

Witkowska, Malgorzata Danuta

[Thesis]. Manchester, UK: The University of Manchester; 2013.

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Abstract

The aluminium AA1050 alloy, known as commercially pure aluminium, contains 99.5% Al, together with Fe and Si as major alloying elements. During fabrication of aluminium substrates for lithographic printing plates in Bridgnorth Aluminium Ltd, the AA 1050 aluminium alloy proceeds through various stages of thermomechanical processing, with the conditions at each processing stage influencing the microstructure of the final coil. Because of its specific gravity, tensile strength, surface performance and coating adhesion behaviour, the AA 1050 aluminium alloy is one of the preferred materials for offset printing, which has been the dominant printing process for years. During manufacturing of the offset plate, the AA 1050 alloy is subjected to alkaline etching, electrograining and anodizing. Reactivity of the material to those chemical and electrochemical processes depends on various alloy properties, the thickness and composition of oxide film over the macroscopic alloy surface, cold work applied and the presence of second phase particles, which influence properties and quality of the final product.During the project, the main objectives were to understand the process in the production of the final product from slab to coil as well as to investigate some microstructural changes during the following stages of the production process and, finally, the performance behaviour of the final product.The set of experiments, including microstructural observation and electrochemical tests, has been developed to investigate the AA 1050 aluminium sheet in accordance with the objective of this study. Four homogenisation trials in the industry environment were performed to enable sample collection from the real production line; also, samples from each processing stage were examined with the special attention paid to those collected during the plant experimental homogenisation trials. It was found that the microstructure of the aluminium changed throughout the different production stages and influences the material response in the alkaline solution used for etching. Furthermore, the conditions of homogenisation (time and temperature) have impact on the properties like the electrochemical behaviour in alkaline and acid solutions, as well as the microstructure of the final aluminium sheet. Differentiation between the behaviour of final gauge samples was possible in terms of characterisation of the second phase particles characterisation (distribution and composition) present in the resultant alloy product.