The Deformation Behavior And Microstructure Evolution Of5A06Aluminium Alloy Under Complex Stress Conditions

Complex components were always under complex stress states in their process offorming or service. When we study the deform, streess or strain state and limit carrryingcapacity of a component, comprehensive and accurate data of material properties andmicrostructure is needed. The deformation behavior and microstructure evolution of5A06aluminium alloy under complex stress state has been systematicly studied in thisthesis. The experiments mainly include three aspects. First was about pre-loading ontwo different direcion, including rolling direcion and perpendicular to rolling direction.Pre-loading on perpendicular to rolling direction was achieved through tensile test ofwide plate. Second was about cruciform biaxial tensile test and the third was forminglimit experiments under room temperature and high temperature. These three aspectssimulated three different complex stress state suffered by materials. Mechanical test,EBSD, SEM, TEM were adopted to analysis the deformation behavior andmicrostructure evolution of5A06aluminium alloy under complex stress state.Pre-loading on the two direction had significant influence on mechanical propertiesand microstructure of the samples and they had consistent trend with the change ofpre-strain. The yield stress increased and the elongation decreased with the increasing ofpre-strain, while the tensile stress changed little. But the two ways of pre-load had a bigdifference on the degree of influence. If the pre-loading was on the transverse directionand the subsequent loading was on the rolling direction, the variation of yield stress andelongation was smaller than pre-load on the rolling direction. With aspect to the tensilestress, the samples of pre-loading on transverse direction had higher value. Thedifference of mechanical properties was mainly caused by the motion path and plugways of dislocation. As regard to bi-direction tensile test,5A06aluminium alloy underdifferent load paths had different stress-strain relationship and different yield locus.When the load on the two direction were equal, the reinforcement effect of material wasthe highest. when pre-loading on two direction at the same time, materials had higheryield stress and lower elongation, while the maginitude was less than pre-loadinguniaxially.Forming limit experiments under room temperature and high temperature werealso studied. The forming limit experiment under room temperature obtained conclutionthat the ultimate strain of samples varied with the sample width. When the stress state was closer to equal tensile, samples had bigger deformation. According to the results ofmicrostructure analysis, different locations of FLD samples had different strain, andtheir microstructure was also different. The samples with different width also haddifferent microstructure. The difference of microstructure mainly existed inmicrostructure morphology of grain boundary, grain misorientation angle, pole figureand the dislocation morphology. The results of tensile test and forming limit test on hightemperature had showed that5A06aluminium alloy had better forming performanceunder high temperature. The TEM results showed that dislocation reply happened whendeforming under high temperature, sub-grain and small-angle grain boundaries can beclearly observed. On the other hand, EBSD results showed that the orientation of grainshave changed.According to the results of research above, we can have a better understanding ofthe stress-strain relationship and microstructure evolution of5A06aluminium alloyunder complex stress state, and it can lay a foundation to the optimization of formingprocess and compents shape.