Transformation of Surface Roughness of Mg Alloy Tubes During Laser Dieless Drawing

Abstract

The paper investigates the transformation of surface roughness of tubes made from magnesium and magnesium alloys as a function of their longitudinal strain during laser dieless drawing. Experimental studies on three materials (AZ31, MgCa08, and pure Mg) have shown that the dependence of roughness on the longitudinal strain is nonlinear and exhibits a minimum. The proposed explanation for this is that the transformation of surface roughness occurs following two mechanisms. The first mechanism involves stretching of the tube and the decreasing of existing roughness with the increasing elongation. The second mechanism is based on the strain-induced surface roughening phenomenon. This mechanism leads to an increase in roughness with the increasing elongation. To analyze these mechanisms, a numerical model of roughness formation is used. It is experimentally shown that the position of the minimum roughness concerning the tube longitudinal strain is correlated with the stress-strain curve of the material under laser dieless drawing conditions. The obtained results provide a practical way to reduce surface roughness of tubes produced by the laser dieless drawing process. According to the proposed method, to achieve minimum roughness, it is necessary to keep the longitudinal strain under a specific value. This value is close to the strain, which corresponds to the maximum stress on the stress-strain curve of the material for temperature and strain rate, corresponding laser dieless drawing conditions.

Experimental and Numerical Study of Surface Roughness of Thin Brass Wire Processed by Different Dieless Drawing Processes

“…Each grain can have individual mechanical properties. Interpolation of unknown quantities inside grains (displacements and stresses) is based on the fundamental Kelvin solution, transformed for the two-dimensional problem of visco-plastic deformation of an incompressible material [26] expressed by equations:…”

“…Each grain can have individual mechanical properties. Interpolation of unknown quantities inside grains (displacements and stresses) is based on the fundamental Kelvin solution, transformed for the two-dimensional problem of visco-plastic deformation of an incompressible material [ 26 ] expressed by equations: where , , —stresses in nodes on grains boundaries; , —forces that result in increments of displacements and stresses in Kelvin′s fundamental solution; , —displacement increments in nodes on grains boundaries; ν —Poisson’s ratio (for an incompressible material equal to 0.5).…”

“…Failure to show the method of model calibration and insufficient verification of its results are serious shortcomings of this paper. The model calibration methodology using results of nanoindentation measurements has been proposed by Milenin et al [ 26 ]. It was assumed that the statistics in the dispersion of the nanoindentation results over the cross-section of the material can be transferred to the statistics of the flow stress distribution in grains of the microstructure.…”

Achieving thin wall and high surface quality of magnesium alloy tubes in combined process of hollow sinking after die-less mandrel drawing

“…The aim of this study is to achieve a thin wall and low surface roughness in the fabrication process of Mg alloy tubes. Although die-less mandrel drawing is suitable for fabricating thin-walled microtubes, it often increases the outer surface roughness [24,25]. Kishimoto et al reported that the slip deformation of the pyramidal slip system was mainly responsible for the roughening of the outer surface in die-less mandrel drawing [26].…”

Investigation of the workability and surface roughness of thin brass wires in various dieless drawing technologies

“…That is why the study of texture and microstructure was also necessary to explain the strain-induced roughness changes. The roughness problem was a subject of our previous study by theoretical [21] and experimental [22] methods, but an effect of MPDD on the product roughness has been omitted in the literature. Thus, this effect was a part of the present study.…”