Analysis Of Superplastic Uniaxial Tensile Mechanics And Structure

For more than half a century, scientific researchers have carried out extensive researches in superplasticity mechanism,metallurgy,mechanical properties and application of technology of materials. Started observing superplastic phenomenon with certain metals and alloys,and study its mechnical properties in further,the reacher of superplastic has traversed a long time. But there are many areas haven't been developed or fully developed in superplastic deformation mechanisms and materials. Superplasticity of application still has a great room for expansion.The superplastitiy of Zn-Al alloy is very high. You can use this characterisitic to form instrument and other part of electrommunication. It also used in artwork. This kind of alloy has wide superplastic deformation temperature range and wide speed range. The alloy will appear an extension of more than 2000 and low flow of stress under the condition of superplasticity. So we can forming pieces shell and other parts by squeezing or gasing. The structure of Znic aluminum eutectic alloy is extended after rolling and can be applied directly to superplastic forming. This is because of that the structure complted the refining process by dynamic recrystallization during deformation. Zinc aluminum eutectic alloy is a typical superplastic materials.The plasticity of Al-Si alloy is not very good. Aothough this kind of alloy can get fine equiaxed grains, Si particles grew up and the formation of the hole limited the development of plastic during the thermal deformation. Since the plastic of this kind of alloy is limited, so it only be used in foundry products.In the researching of superplasticity, the research of invariable temperature occupied important positions. The characteristics of superplastic under invariable temperature are: strain rate sensitivity, no yielding stress and no strain hardening. Therefore wuperplasticity tensile parameters the strain rate sensitivityindex, strain hardening index and stressrelaxation index are important mechanical indicators.Plastic of metal changes with its organizations and its deformation conditions. Firstly introduce and analysis the structure changes briefly during superplastic deformation. On this basis, make a discussion on a representative micro-theory. The reason of structure changed when superplastic deformation is the common result of the stress and heat activation. Research the structure changes of superplastic deformation in order to predict the mechanical properties and access certain basic information of micro-mechanism.This dissertation mainly analyse the mechanical parameters and microstructure in the state of instability by the experiment of superplastic tensile deformation. And then try to connect the macro-mechanical parameters with the micro-mechanism.The measuring methods of mechanical parameters in superplastic tension and the judgement of tension instability in the dissertation are carried out on the basis of existing theories,which is invented by CAMS.Song Yuquan.Combining the experimental,push the theoretical analysis to a high level.The dissertation is mainly composed by five chapters which includes alladvanced subjects of superplastic tension such as the main parameters'smeasuring methods in tension and analyse the curves which we got inexperiment,instability judgement of quantitative analysis and analysis themicro-mechanism and so on.In the introduction,mainly introducted the thingsrelated with superplastic.The main contents are as follows.1.. Introduction: Introduce criterion of plastic, physical basis of deformation,superplastic deformation mechanism and the development and feature ofsuperplastic. So we can derive the significance. And indicate the paper's content.2 The theoretical foundation of macro-mechanical parameters: Introduce the measure methods of three mechanical parameters respectively, strain rate sensitivity index m, strain hardening index n and stress relaxation index x. Provide the theoretical bases to the further researching of measuring the mechanical parameters.3 The measurement of mechanical parameters: firstly determine the experiments process then adjustment the equipment. Choose typical superplastic material Zn-5%A1 and lower elongation material Al-15%Si as the test material. In the certain temperature make the tensile experiments under constant speed and constant strain rate and the experiments of stress relaxation. According the test curves we have got to confirm the rule of m, n andτchanges and analysis them in theoretically.4 Determine the point of instability and analysis the microstructure ofinstability. Make a connection between macro-mechanical parameter andmicrostructure, by observing the microstructure of the point of instabilityusing metallography.This study just a part of the connection between superplasticitymacro-mechanical regularity and micro physical mechanism. The purpose isthat provide theory basis for the future new materials designing.