Randomization of Recrystallization Textures in an Experimental Al-5%mg Alloy and Aa6111

This dissertation, "Randomization of recrystallization textures in an experimental Al-5%Mg alloy and AA6111" by Sin-ting, Cynthia, Chang, 張倩婷, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Randomization of Recrystallization Textures in an Experimental Al-5%Mg Alloy and AA6111 Submitted by Chang Sin Ting Cynthia for the degree of Doctor of Philosophy Department of Mechanical Engineering at The University of Hong Kong in October 2005 This study investigates two aluminium alloys, Al-5%Mg and AA6111. They are both candidate materials for automobile body panels. The aim of study is to investigate the effect of different parameters on the recrystallization textures through different thermo-mechanical processing routes. The ultimate aim is to produce aluminium alloy sheets which have high drawability after recrystallization ensuring good press shop performance during car body production. For the Al-5%Mg alloy, the hot band materials were cold rolled 95% at two rolling o o speeds and annealed at 300 C in an air furnace and at 450 C in a salt bath. To investigate the effect of rolling strain on the recrystallization textures, intermediate annealing was added in between the rolling processes. Also, asymmetric cold rolling was performed. The recrystallization textures of Al-5%Mg were mainly affected by the annealing temperatures. At low annealing temperature, the major recrystallization textures were Cube and R/S. For high annealing temperatures, Cube, ND Rotated Cube and Q components are dominant. The strength of the Cube texture is governed by four important factors; nucleation rate, volume fraction of Cube material, distribution and growth range of Cube nuclei. The R/S texture originates from the internal necks that were produced during cold rolling. The S grains formed internal necks and had scattered orientations, and from these orientations a subset of nucleus having a 40 provided the successful recrystallised grains of orientation R/S. For the AA6111, the hot band was divided into two batches. The first batch was directly cold rolled 80%. For the second batch, the hot band was first solution heat treated (SHT) before the cold rolling. The cold rolled samples were then annealed at o o o three different temperatures (450 C, 500 C and 540 C) in an air furnace. The recrystallization textures of AA6111 were strongly affected by the initial precipitation states before anneal. The samples after SHT, which were in the supersaturated solid solution state before annealing, produced precipitates mostly along grain boundaries and sub-boundaries during the anneal. These small precipitates hindered both particle stimulated nucleation (PSN) and other nucleation sites, but the pinning involved in PSN was more severe. Therefore the final recrystallization textures did not contain any textures arising from PSN. For the sample without SHT, precipitates were aligned parallel to the rolling plane balanced after cold rolling, thereby producing planar arrays of precipitates. These precipitates proved capable of pinning the Cube nuclei but not nuclei associated with PSN, and therefore PSN textures were more dominant after recrystallization. The main aim of this study was to produce weak or near random textures. A rather weak Cube in a mixture of other texture components produced balanced and weak recrystallization textures in Al-5%Mg when intermediate rolling was used. A very weak texture in AA6111 was also obtained by employing SHT treatment before cold rolling. These processing routes were successful in producing