In Situ EBSD Studies Of The Plastic Deformation Within Grain/Subgrain Of Aluminum Alloys

Aluminum alloys were selected to be the proper candidate for use in fabricatingof high speed train, because of its high strength/density ratio, good resistance tocorrosion and good shaping ability. During its working process of high speed train, thecomplex stress applied on the body and components will cause fatigue or even failurein local region after long time serve which is harmful to the safety traffic. Thelongitude stress generated during start and break, the transverse stress generated whenpassing through tunnel and train crossing will introduce plastic deformation in the keycomponent. Therefore, study of the plastic deformation of Aluminum alloy willsupply experimental and theoretical principle for the safety traffic of high speed train.Study of the deformation texture is one of the main consideration of materialsscientist. The texture of materials evolves under the effect of strain stress. Forspecimen subjected to tensile or compressive deformation, the restriction of grips andneighboring grains will alter the orientation of grain and consequently the texture ofspecimen. Until now, many models such as Sachs, Taylor and self-consistent modelsare raised up and can predict the main texture of materials, with errors on someorientations. The theoretical models lie in the effect of initial orientation, the numberof slip system active, the interaction among slip systems. In situ tensile deformation ofmetallic materials gives up an opportunity to study the plastic deformation behaviorswithin individual grain or subgrain and can supply experimental and theoreticalprinciples in set up models of texture evolution and plastic deformation of materials.Using a tensile stage and electron backscatter diffraction equipped in a scanningelectron microscopy, the plastic deformation behaviors within individual grain andsubgrain of a commercial Al-Mg-Si alloys were in situ studied to reveal the grainrotation behaviors and its corresponding crystallographic mechanism. The mainconclusions can be drawn in the following:1) Evident rotation of grain orientation was observed during plastic deformation ofAluminum alloys. The orientations distributed around <101> and in the center ofthe inverse pole figure mainly rotate towards the line of <001>-<111> and part ofthem rotates toward <111> direction.2) For specimen subjected to tensile deformation, there are three plastic deformationand rotation behaviors observed in the selected grains: a. dislocations slip on onemain slip system and corresponds to only one rotation trend; b. dislocations slipon two or more slip systems and corresponds to two or more rotation trends; c.the orientation of grain rotates in a trend opposite to the theoretical prediction.The results indicate that the plastic deformation of individual grain has toaccommodate the deformation of its neighboring within and among grains.3) The Kernel average misorientation (KAM) increases with increasing external strain with a higher value on the grain boundary than inside the grain. The KAMvaries within grain and among grains. The results indicate that plastic strainincreases with increasing external strain. The deformation strain on the grainboundary is higher than inside of grain. The plastic deformation isinhomogeneous within grain and among grains.4) The rotation of grain orientation leads to the increase of the angle (θ) between theorientation parallel to the loading axis and the normal direction of slip plane anddecrease of the angle (φ) between loading direction and the shear direction.Therefore, the rotation of grain orientation can either leads to increase or decreaseof Schmid factor depending on the initial orientation and angles between thenormal direction of slip plane and the shear direction. The evolution of Schmidfactor within grain can also show different evolutions among different parts.5) In part of the grains, dislocations active on only one main slip system with themaximum Schmid factor, without excluding slip of dislocations on other slipsystems without clear traces on the grain surface which satisfying the Sachsmodel. Slip of dislocations in most of the grains is on2main slip systems whichis between the Sachs and Taylor models. Slip of dislocations in minor grains is onmore than2slip systems, which satisfying the Taylor model. Dislocation slips on2or more slip systems is attributed to the plastic deformation accommodationrequirement of neighboring grains to make the stress/strain consistency amongdifferent parts of grains or within grains.6) For grains with similar initial orientations, the lattice can rotate in different trendswhich is influenced by the accommodation effect of neighboring grains.