Experimental Study On Micro-isothermal Extrusion And Forming Mechanism Of ZL101Alloy In Semi-solid Zone

With the rapid development of electronic industry, telecommunication,medical equipments and exact mechanism, the miniaturization of machines isalready a trend. As a rising technology, microforming technology has obviousadvantages of high material utilization and stable property of products. Also itwill play an important role in the mass production and efficient production ofmicro devices. As the microforming technology is still in the primary stage of itsdevelopment, there are so many unknown in the aspects of forming theory,forming process, manufacturing of equipments, precision control and so on.Therefore there is still a long way to go before this kind of technology isintroduced into commercial production.In this thesis, the widely used aluminum alloy ZL101was chosen as theraw material and the effect of different process parameters on forming loadduring micro extrusion was studied. At the same time, micro structurerevolution，forming mechanism and liquid phase segregation during the formingprocess were also discussed.The experimental mould for micro extrusion was designed regarding to thecharacter of isothermal micro extrusion. High temperature ceramic heater wasused to heat the raw material. During the process, the AT-908artificialintelligence temperature control device was chosen to monitor the formingtemperature exactly. When required temperature is arrived, CMT-4000electricuniversal testing machine was used to complete the extrusion. Different solidfraction (deformation temperature), extrusion ratio and extrusion velocity wereselected. As it can be found from experimental results, solid fraction, extrusion ratio and extrusion velocities are all key factors that wound affect theload-displacement curves of micro extrusion. The maximum extrusion forcesteadily rises as the extrusion ratio and extrusion velocities rise. Also themaximum extrusion force rise with the decrease of solid fraction. However,there is no severe load fluctuation or unusual rise during forming process as theforming feature approach the grain size.Through analysis based on load-displacement curve, micro structure ofextruded part and remaining billet, the structure evolution model, formingmechanism and liquid phase segregation were demonstrated. Extrusion velocityaffects the liquid phase segregation seriously. This defect would be relieved withthe rise of extrusion velocity. The α-phase would undergo the melting of grainboundary, aggregation, ripening and globalization during the reheating process.And unlike the forming mechanism of upsetting, both slippage and rotation ofsolid phase with lubrication of liquid phase and plastic deformation of solidphase contributes during micro extrusion of ZL101.Visco-plasticity finite element analysis technology was also introduced inthis thesis. Material model of ZL101aluminum alloy at semisolid state wasdefined on the software platform of DEFORM-2D V9.01. Then micro-part bymicro extrusion was analyzed and comparison between the analytical results andexperimental results was done. It shows that, analog results are of directed andreferential meaning.