Study of mechanical properties of aluminium-based sheets for structural applications : role of processing parameters

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Study of mechanical properties of aluminium-based sheets for structural applications : role of processing parameters

 

Author: Cheung, Ka Po
Title: Study of mechanical properties of aluminium-based sheets for structural applications : role of processing parameters
Degree: Ph.D.
Year: 2014
Subject: Aluminum alloys -- Mechanical properties.
Metallic composites
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: xx, 207 leaves : illustrations (some color) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2757531
URI: http://theses.lib.polyu.edu.hk/handle/200/7525
Abstract: Interest in nanomaterials has been increased in recent years because of their superior properties such as high strength, compared with their coarse grained counterparts. The sample sizes of nanomaterials are often too small for practical use due to the limitations of current fabrication methods. Nevertheless, because of the increasing demand for high strength materials for their aviation and industrial applications over the last two decades, a wide variety of metal alloys such as aluminium has been investigated recently. The present study systematically investigates the relationship between constitutive behaviour and localised structure in aluminium-based alloy which has been exposed to surface mechanical attrition treatment (SMAT), in conjunction with warm/cold rolling technology. Among these two methods, SMAT is the more promising synthesis methods to fabricate nanostructured materials in bulk form with superior yield strength at low cost. However, adopting SMAT alone always results in rather low ductility. Hence, the processing techniques and routes that have been currently adopted to improve their mechanical properties are then addressed. In this work, other preliminary studies and current topic related to surface nanocrystalline (SNC) of materials were reviewed. The process of fibre metallic glass laminates (FMGLs) production was also studied, with a view to enhancing ductility. FMGL, composed of Al-based metallic glassy ribbons and fibre/epoxy layers (prepreg), was developed to address the need of high performance lightweight structures with excellent mechanical properties. A new method for manufacturing FMGLs with bulk material is emerging as a result of the demand for more efficient and lightweight materials in automotive and aerospace industries. This concept induces excellent strength-to-weight ratio comparing with pure metals through tension and flexure. Extensive experiments were carried out to analyses the physical and mechanical properties for characterize the behaviour of the working processes. The findings are significant in 4 aspects: (1) the strengths of aluminium sheets are successfully enhanced after SMAT, (2) the effect of SMAT produced not only the nanostructured layer, but also some compressive stress on the surface layer of the aluminium sheets, (3) the higher the percentage of reduction in thickness during the rolling process, the higher the strength of the rolled samples that could be obtained, and (4) the ductility of FMGL is improved under both tensile and bending conditions compared to monolithic metallic-based bulk metallic glasses (BMGs). These provide a good insight into the influence of the structure after severe deformation caused by surface mechanical and heat treatment. After the surface nanocrystallization technologies and hot working processes, the treated material exhibits remarkably high strength and exceptional ductility as a result. The combination of these aspects makes aluminium alloys a strong candidate for aerospace applications such as enhancing the future structural design of aircraft fuselage. The present study might provide a research direction for future development of such materials.

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