Severe plastic deformation by linear flow splitting

Abstract

Due to the new linear flow splitting forming process the production of bifurcated profiles from sheet metal without lamination of material becomes feasible. The continuous production of such structures takes place incrementally in a modified roll forming machine. By producing those complex parts process-related changes in the material properties occur as a result of the cold forming. Thus, the assumption of homogeneous properties in the processed part is not valid and a reliable analysis of structural durability is only possible by considering changes in material properties. Investigations on linear flow split profiles show large gradients in the microstructure and properties over the profile cross section. In the areas of low plastification the degree of deformation and the flow stress can be determined by microstructure and hardness measurements. In the severely deformed areas, like the upper flange surface, this determination becomes doubtable. Therefore the electron backscattered diffraction method was used to investigate, if an ultrafine-grained structure is occurring as it evolves in the processes of severe plastic deformation. Thus, the aim of this paper is the numerical analysis of the linear flow splitting process, the metallographic characterisation of bifurcated profiles and the numerical evaluation of the structural durability with consideration of the gained insights

Properties of UFG HSLA Steel Profiles Produced by Linear Flow Splitting

“…Thus, the local strength can only be calculated from the hardness. Earlier investigations on the correlation of hardness and yield strength in bifurcated HSLA steel profiles processed by linear flow splitting led to an empirical equation derived from the well known Ludwik-equation [3]: Table 1 shows the good compliance between measured and calculated yield strength with a maximum deviation of less than 4%. Thus the strength in the region with the smallest grain size close to the flange surface can be calculated with adequate accuracy to ~1000 MPa.…”

“…Earlier investigations have shown that linear flow splitting induces severe plastic strain which leads to the formation an ultrafine grained (UFG) microstructure in the regions of strongest plastic deformation, i.e. the splitting center and the flange surface [3]. In contrast to typical severe plastic deformation (SPD) processes as equal-channel angular pressing (ECAP) [4,5] or high pressure torsion (HPT) [5,6], linear flow splitting is characterized by inbuilt deformation gradients in the processing zone and a change in geometry of the semi-finished part.…”

Influence of Gradients in the Elastic Anisotropy on the Reliability of Residual Stresses Determined by the Hole Drilling Method

“…Earlier investigations on HSLA steels have proven this method to be a suitable approximation [10]. Grain orientation measurements using EBSD were carried out at the corresponding positions of the hardness measurements in order to obtain textures and elastic properties.…”

Mechanical properties of the AlSi1MgMn aluminium alloy (AA6082) processed by gradation rolling

“…Accordingly the formation of thin ultrafine-grained layers is achieved. Popular methods are the surface mechanical attrition treatment [13], linear flow splitting for flat products [14] or spin extrusion for tubes [1,15].…”