Study Of Volume Effect On The Plastic Flow Behaviors Of Metal

The metal plasticity index is usually associated with a deformable body size （ordimension）, namely, the existence of the so-called " volume effect". For example, somestudies show that，within a certain range, the deformation body volume is bigger, themacro plastic expression is low; and when the volume reaches a critical value, theplastic will no longer with the volume increase and reduce. In addition, the deformationresistance will also as volume decreases. The practice of plastic processing, especiallysome "large" or "ultrafine" parts of the forming, need to consider the difference of thematerial properties of this volume of different sizes.This paper focuses on the relationship between the deformation of the volume andmetal plasticity index. We do series of mechanical properties test with different volumeratio of metal material sample to proved size on metal plastic indexes. At the same time,combination of numerical simulation analysis of high temperature deformation process.By45steel,AZ31magnesium alloy and aluminum alloy6061three kinds of metalmaterials at high temperature hot compression simulation test found that, at a strain rateunder0.1s^-1conditions, true stress will increase as the sample size increases. In view ofthis phenomenon, from the macroscopic deformation geometry size and microstructurewere analyzed. Discovery of deformation geometrical inhomogeneities of bigger, testthe calculated stress value is increasingly big, deviate from the true values far;microstructure not only in the same sample was irregular, but also in the proportion inwhole volume sample difference. Combined with finite element numerical simulation,analysis of microstructure change on true stress effect.High temperature tensile tests showed that cross-sectional area of large specimensof the maximum stress is large, but for the indicators of metal-plastic elongation andarea reduction, it is the cross sectional area of small sample values larger.Experiments show that,45steel and AZ31magnesium alloy at room temperaturecompression deformation resistance decreases as the volume increases, while the6061aluminum alloy at room temperature compression deformation resistance increases withthe sample size did not change significantly. The room temperature tensile test of thetrue stress-true strain curve with no significant difference, but the variation ofelongation and area reduction rate is the same as the high temperature tensile.