| As a common magnesium alloy, Mg-Mn alloy is widely used. It has goodcorrosion resistance in saline solution, and easy to welding. The room temperature andhigh temperature mechanical property of the magnesium alloy is greatly improved withthe addition of Ce. Among those, MB8and ME21are the typical alloys. The MB8canbe used as high-temperature alloy, and the ME21was used as wrought alloy in Germanywhich can be deformed at at high temperature so as to reduce equipment cost andproduction cost due to the increasing of extrusion speed and reducing of the extrusionpressure. ME21magnesium alloy is mostly used as low cost sheet at home recentlyyears which could be produced by extrusion and rolling. As a commercial alloy used forextrusion product, there is no report about the investigation on influence of extrusionprocess on microstructures and mechanical properties in China. In this paper, thehomogenization process of ME21magnesium alloy was optimized by industry test,the hot deformation behavior was investigated by hot torsion test, and the influence ofextrusion temperature on microstructures and mechanical properties of extruded rod andextruded plate was analyzed.The results are following:The homogenization process with temperature of380℃，420℃and460℃, time of8h,12h,16h and24h was investigated. The results show that homogenizationtemperature has influence on the grain size of alloy. It can get highest and lowesthardness at380℃×8h and460℃×24h respectively. After different homogenizationtreatments, the samples were subject to hot extrusion which can get the highest roomtensile strength with380℃×8h and the highest room plastic with420℃×12h.The hot torsion test was done on the NWS500computer controlled hot torsionmachine. The flow behavior of ME21magnesium alloy was investigated with thetemperature range of300~450℃and the strain rate range of0.0001s-1~0.01s-1. Thedynamic recrystallization occurs obviously at high temperature. The results show that atthe torsion temperature450℃and equivalent strain rate0.01s-1, its equivalent strain isover1.1before fracture. That means the alloy is suitable for high temperature highspeed deformation. The constitutive equation for high temperature deformation ofME21magnesium alloy by hot torsion test was established on statistical regressionanalysis using Zener-Hollomon parameter. The relationship between recrystallized grainsize and strain rate compensation parameter Z, and the microstructure differences at different positions on the same cross section caused by different degree of deformationwere investigated.The extrusion experiment was under500T extrusion machine. The extrusionproducts were φ16mm rod and3*60mm sheet, the extrusion ratio are28and31.5respectively. The extrusion temperatures of extruded rods were350℃，380℃，410℃，430℃,450℃,and the sheet were350℃，380℃，410℃，440℃. The results show thatextruded rods can get the highest tensile strength at lower temperature350℃and thehighest elongation at higher temperature450℃. The mechanical properties differencesfrom three directions of sheets products are very huge. For the extrusion temperature380℃, the mechanical properties from three directions of the extruded sheet are good.The range of tensile strength is from252MPa to264MPa, the yield strength is from219MPa to223MPa, and the elongation is from16.2%to23.0%. At the direction of90°, the tensile strength is the highest, while at the direction of45°the elongation isthe highest. The annealing treatment process was at the temperature350℃and400℃，and the annealing time was1h,2h,3h and4h. After the annealing treatment, theelongation had different degrees improvements. Proper annealing treatments can reducethe anisotropy both strength and elongation. When the annealing temperature of400℃and the annealing time of2h were adopted， IPA of the tensile strength and theelongation were reduced to3.8%and7.8%. It shows that400℃×2h is the best choiceto reduce the anisotropy. |
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