04-13-2018, 03:33 AM
Aluminum alloy has played an important role in lightening automobiles with hydroformed aluminum tubes making it possible to create lightweight parts with spatial structures and complex sections that can replace steel in high-end cars, and achieve energy savings and emission reductions. The first aluminum alloy rear axle subframe made by hydroforming was used in the 5-series BMW(Bayerische Motoren Werke), with its total weight of only 11.5 kg achieving a significant weight reduction when compared to steel . Audi have since manufactured roof rails by hydroforming 6014 aluminum alloy and used these in their A2 and A8 series vehicles to reduce their body weight by 40%
Surface roughening occurs on the surface of aluminum alloy tubes during hydroforming deformation, and when the surface roughening is severe enough, it produces surface defects such as “orange peel” or ridging and roping that affects the industrial production negatively [9,10,11]. It is widely accepted that such materials have an anisotropic behavior and different crystal orientations, which leads to incompatibilities of deformation arising from interactions between neighboring grains. The surface roughening behavior attributable to the deformation of individual grains can generally be observed on a grain scale , and so the most basic influential factors include internal factors (mainly grain size) and external conditions (mainly strain) .
The factors that influence surface roughening have mostly been investigated through tensile deformation, bending experiments and also cup drawing tests . Under a uniaxial stress state, the surface roughness first increases then decreases slightly with increasing strain, but increases linearly with increasing grain size [15,19]. Other studies have found that the surface roughness increases linearly with both increasing grain size and strain [17], but very few reports have paid attention to surface roughening under biaxial stress conditions. One study investigated the relationship between surface roughness and strain using numerical simulation, but this was neither verified by relevant experiments, nor did it consider the relationship between microstructure and surface roughness of tube during hydroforming .
In this study, bulging tests were carried out using 6063 aluminum alloy tubes with different microstructures to determine the quantitative relation between surface roughness, strain and grain size under biaxial stress. For this, tubes with different grain sizes and textures were prepared by spinning and annealing, and different strains were obtained by changing the area of the bulged tube. Measurements of surface roughness and observations of surface topography were also carried out using a confocal scanning laser microscope. Microstructural information was obtained using electron back-scattered diffraction (EBSD).
Surface roughening occurs on the surface of aluminum alloy tubes during hydroforming deformation, and when the surface roughening is severe enough, it produces surface defects such as “orange peel” or ridging and roping that affects the industrial production negatively [9,10,11]. It is widely accepted that such materials have an anisotropic behavior and different crystal orientations, which leads to incompatibilities of deformation arising from interactions between neighboring grains. The surface roughening behavior attributable to the deformation of individual grains can generally be observed on a grain scale , and so the most basic influential factors include internal factors (mainly grain size) and external conditions (mainly strain) .
The factors that influence surface roughening have mostly been investigated through tensile deformation, bending experiments and also cup drawing tests . Under a uniaxial stress state, the surface roughness first increases then decreases slightly with increasing strain, but increases linearly with increasing grain size [15,19]. Other studies have found that the surface roughness increases linearly with both increasing grain size and strain [17], but very few reports have paid attention to surface roughening under biaxial stress conditions. One study investigated the relationship between surface roughness and strain using numerical simulation, but this was neither verified by relevant experiments, nor did it consider the relationship between microstructure and surface roughness of tube during hydroforming .
In this study, bulging tests were carried out using 6063 aluminum alloy tubes with different microstructures to determine the quantitative relation between surface roughness, strain and grain size under biaxial stress. For this, tubes with different grain sizes and textures were prepared by spinning and annealing, and different strains were obtained by changing the area of the bulged tube. Measurements of surface roughness and observations of surface topography were also carried out using a confocal scanning laser microscope. Microstructural information was obtained using electron back-scattered diffraction (EBSD).