Study On Size Effect Of Asynchronous Electric Rolling AZ31B Magnesium Alloy Foil

During the rolling of AZ31B magnesium alloy strip,the work hardening caused by grain size effect becomes more and more significant with the increase of rolling passes,which makes it difficult to carry out subsequent processing.When the AZ31B magnesium alloy strip is thinned to a certain extent,the grain size effect often causes defects such as edge crack of magnesium alloy foil.In this study,the size effect phenomenon in the rolling of magnesium strip(thickness 0.6mm)and magnesium foil(thickness 0.1mm)with three grain sizes(5μm,15μm,40μm)was studied.Using different rolling methods and introducing pulse current,the effects of rolling methods and pulse current on the size effect were investigated,and the electroplastic asynchronous rolling process of magnesium alloy foil was explored.Firstly,based on the uniaxial tensile test at room temperature,the influence of grain size on the mechanical properties and fracture characteristics of magnesium strip and magnesium foil in different directions was studied.In the tensile test,there is a size effect phenomenon in the flow stress of magnesium tape and magnesium foil in all directions.The flow stress of magnesium tape and magnesium foil increases with the decrease of grain size,and the smaller the stronger the size effect.With the decrease of grain size,the fracture mode of magnesium strip and magnesium foil finally transforms into dimple fracture.Secondly,the effects of grain size on the rolling performance and micro deformation mechanism of magnesium strip and magnesium foil,as well as the effects of asynchronous rolling and pulse current on grain size effect were investigated by synchronous rolling,asynchronous rolling and asynchronous electric rolling experiments on magnesium strip and magnesium foil with three grain sizes.In the experiment,the synchronous rolling force has obvious size effect,showing’fine grain strengthening’effect;the anti-Hall-Petch effect occurs after the reduction rate of 7%and 5%respectively in asynchronous rolling and asynchronous electric rolling.EBSD experiments showed that the number of secondary twins increased with the increase of grain size,and asynchronous rolling and asynchronous electric rolling could effectively reduce the number of secondary twins.By comparing the mechanical properties and deformation mechanism caused by grain size effect under three rolling methods,it is shown that asynchronous rolling and pulse current can weaken the influence of size effect.In the experiment,asynchronous electric rolling can reduce the rolling force difference caused by size effect to 0.4k N.Finally,based on the interaction between size effect and asynchronous electric rolling,the electric rolling experiment was carried out.The inflection point of texture weakening and anisotropy weakening of continuous electric rolling was proved by controlling the grain size of rolling inlet by controlling pulse current.In the experiment,synchronous electric rolling and asynchronous electric rolling appeared the points of texture weakening and anisotropy weakening at the current density of 28.5A/mm~2 and 27.9A/mm~2 respectively,and the microstructure was improved during the rolling process to achieve the effect of rapid plasticization modification.Finally,the asynchronous electric rolling of magnesium foil was realized,and 0.07mm magnesium foil was successfully prepared.Exploring the influence law of the size effect of magnesium alloy foil and strip rolling and the influence of electric pulse on the size effect,and studying the efficient asynchronous electric rolling process of magnesium alloy foil and strip are helpful to promote the mass production of magnesium alloy foil and strip,and promote the magnesium alloy to the precision equipment market.