Transformation of Surface Roughness of Mg Alloy Tubes During Laser Dieless Drawing
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JMEPEG https://doi.org/10.1007/s11665-020-05234-6
Transformation of Surface Roughness of Mg Alloy Tubes During Laser Dieless Drawing Andrij Milenin
, Tsuyoshi Furushima, and Jirˇı´ Neˇmecˇek
Submitted: 3 July 2020 / Revised: 27 September 2020 / Accepted: 10 October 2020 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. Keywords
boundary elements method, magnesium alloys, roughness
dieless
drawing,
1. Introduction The process of dieless drawing consists of local heating of the material to the temperature of hot deformation with simultaneously controlled stretching. During stretching, the heating zone moves along the length of the workpiece and stretching appears along the entire length of the sample (except the fixing points). Weiss and Kot proposed this process in 1969 (Ref 1) for the elongation of a wire. The dominant features of this process are the absence of a deforming die and lubrication, which lowers the production costs. The dieless drawing was used by Sekiguchi et al. (Ref 2) for the deformation of bars. They noticed another advantage of this method—the absence of friction. This simplifies the processing of materials with low workability. Extending this idea, Furushima and Manabe (Ref 3) applied a dieless drawing to the elongation of microtubes in superplastic conditions for AZ31 and Zn-Al alloys. Kustra et al. (Ref 4) demonstrated that the dieless drawing process allows achieving a significant elongation of the workpiece in one pass (up to 60%) for MgCa08 magnesium alloy with increased biocompatibility. Supriadi et al. (Ref 5) showed that the dieless Andrij Mileni
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