The Properties And Microstructure Of Pure Magnesium Wire During Cold Drawing Process

Pure magnesium has low density, high specific strength, specific stiffness, goodconductivity and conductive-heat performance, vibration reduction performance andelectromagnetic shielding effectiveness, etc, which makes pure magnesium wirehave extensive application as functional materials in the aerospace, communications,transportation industry. Drawing forming is suitable to processing tube rod wireespecially under Φ2mm wire with high mechanical performance, dimensionprecision and surface quality. But the plastic forming ability of pure magnesium islow at room temperature, and average cold drawing deformation per pass isgenerally not more than10%with frequent annealing treatment in the process ofdrawing, so the production efficiency is low. In this paper, Φ0.625mm puremagnesium wire was obtained from Φ2.0mm magnesium wire by multiple-passdrawing with small deformation per pass without any annealing treatment, andsevere plastic deformation of90%had been obtained. A series of investigationswere discussed such as the effect of deformation in per pass(3%,5%,8%) andcumulative deformation(10%~90%) on microstructure, texture and mechanicalproperties by means of optical microscopy, conductivity tests, electron back scatterdiffraction (EBSD), microhardness and tensile tests at room temperature.With cumulative deformation increasing, the microstructure changes in threedifferent stages. When cumulative deformation is smaller than30%, the number ofdeformation organization increases gradually. When cumulative deformation issmaller than70%, deformation organization gradually reduces. When cumulativedeformation exceeds70%, there is almost no change in the number of deformationorganization, and grain boundary is clear, elongated along the drawing direction.The text of pure magnesium wire transfers to deformation texture fromrecrystallization texture with the increase of accumulative deformation. When thecumulative deformation is90%, average Schmid factor along the drawing directionis0.144, forming a strong fiber texture.The change of pure magnesium wire microhardness can also be divided intothree intervals along with the increase of cumulative deformation. In the first stage,the microhardness increases significantly. In the second stage, microhardnessgradually reduces, and the greater single-pass drawing deformation is, the moreslowly microhardness decreases. In the third stage, the microhardness has notobviously changed. When single-pass drawing deformation is3%,5%and8%, thecumulative deformation at the end of the first stage increases gradually, followed by25%30%35%respectively and the corresponding microhardness increases slightly. Microhardness increases gradually with single-pass drawing deformation increasingat cumulative deformation of70%and90%.The change of pure magnesium wire yield strength can also be divided intothree stages along with the increase of cumulative deformation. In the first stage,yield strength increases to170MPa significantly. This is because strong workhardening, a degree of fine-grain strengthening and texture strengthening. In thesecond stage: when single-pass drawing deformation is3%, yield strength decreasesgradually; When single-pass drawing deformation is5%, yield strength changeslittle; When single-pass drawing deformation is8%, yield strength rises lightly. Thecumulative deformation at the beginning of the second stage increases graduallyalong with the increase of single-pass drawing deformation. This can be explainedthat continuous dynamic recrystallization softening materials occurs. The greatersingle-pass drawing deformation is, the more fully continuous dynamicrecrystallization develops, then the faster yield strength decreases. In the third stage,yield strength increases obviously. And yield strength has been improved to214MPaat cumulative deformation of90%because of strong fiber texture.