Study On The Character Of Orientation Of Ultrafine-grained Aluminum Alloy Prepared By Friction Stir Processing

At high stain rate and forced cooling condition, ultrafine-grained aluminum alloy isproduced by friction stir processing The orientation of grain and grain boundary mustbe different from coarse grain material and other ultrafine-grained material processedby other methods. Grain orientation and grain boundary orientation have an importantinfluence for macroscopic property of material, furthermore, the distributions of grainorientation and grain boundary orientation can reflect deformation mechanism ofmaterial to a certain extent.Ultrafine-grained aluminum alloy was prepared by friction stir processing incirculating water. cooling conditon The microtextures of friction stir processed regionswere detected. The character and evolution of grain during friction stir processing wasstudied. The tensile test with different initial angle and detection of macrotexture weretaken for ultrafine-grained aluminum alloy. The effect of grain orientation onmechanical property of ultrafine-grained aluminum alloy was analyzed. Hightemperature tensile test and detection of microtexture before and after deformationwere taken. The mechanism of high temperature deformation was studied throughanalysis of grain orientation and character of grain boundary. The major findings are asfollows: Using friction stir processing technology in circulating water cooling medium canprepare ultrafine-grained material whose the average grain size is0.64um.Ultrafine-grained aluminum alloy located stir zone exists {113}<110> preferredorientation. The distribution of misorientation present bimodal phenomenon which are3°and47°, respectively. Its proportion of high angle grain boundary is86%. Inthermo-mechanically affected zone, the {001}<110>R-cube is preferred orientationand the proportion of high angle grain boundary is37%. The {124}<211>R preferredorientation exists in the base metal that the proportion of high angle grain boundary is95%in. The continuous dynamic recrystallization is the main mechanism of grainrefinement in stir zone.(332)[110] texture existed in ultrafine-grained aluminum alloyresults in the anisotropy of mechanical property. The hot deformation mechanism ofultrafine-grained aluminum alloy is mainly divided into three phases:(1)150℃to250℃: the main deformation mechanism is dislocation glide. Dynamic recovery ismain softening mechanism.(2)250℃to400℃: the main deformation mechanism isdislocation glide, supplemented by grain boundary sliding. Dynamic recrystallizationis main softening mechanism. Subgrain superplasticity occurrs.(3)400℃to450℃:the size of grain growth rapidly and is uneven. Because grain boundary is soft interface,that intergranular-ductile fracture take place.