Research On Mesoscopic Forming Limit Of GH4169 Alloy Sheet

With the rapid development of electronics and precision machinery in recent years,the forming of fine parts is becoming more and more important.With the development of miniaturization of structure,the demand for micro parts will be increasing,and the forming technology of producing micro parts with high precision and low price will be very promising.Due to the existence of size effect in microforming,the technology of forming microparts is still limited in industrial production.That is,with the decrease of characteristic size t/d,the sheet material is prone to produce uneven plastic deformation and early strain concentration,and the forming limit shows an obvious downward trend and the fluctuation of the limit strain data increases.The macroscopic forming limit prediction model can not consider the influence of size effect,so there is a big deviation in predicting the forming limit of sheet metal.However,nickel-based superalloy sheet has complex microstructure and strengthening mechanism,and the existence of precipitates affects the forming limit size effect at meso-scale.How to construct the forming limit model of nickel-based superalloy sheet at meso-scale is of great significance for its application in microforming.In this paper,Holmberg and Marciniak experiments were carried out on the meso-scale forming limit of GH4169 nickel base superalloy sheet.The influence of size effect and precipitation on forming limit was investigated,and then a prediction model of meso-scale forming limit of GH4169 nickel base superalloy sheet was established.The core content of this paper is mainly divided into three parts:(1)Experimental study on mesoscopic forming limit of GH4169 alloy sheetBased on the meso-scale Holmberg and Marciniak experiments,the forming limit diagram of the thin sheet of GH4169 nickel-based superalloy with different grain sizes and ???/?? phase content was obtained by Digital image correlation(DIC)technique.The effects of different grain sizes and precipitates ???/?? on the ultimate strain,strain path and deformation process under different loading paths were analyzed.The results show that the ultimate strain decreases with the increase of grain size,but increases when the grain size increases to a certain extent,and the fluctuation of the ultimate strain data increases significantly,showing obvious size effect.In addition,the existence of ???/?? phase can significantly reduce the ultimate strain of the sheet and affect the forming limit size effect of GH4169 alloy sheet.(2)Modeling of mesoscopic forming limit of GH4169 alloy sheetBased on the macroscopic forming limit prediction model,the forming limit diagram of GH4169 alloy sheet was obtained,and the feasibility of prediction model for GH4169 alloy sheet was analyzed.The matrix phase constitutive equation and???/??phase constitutive equation of GH4169 nickel base superalloy sheet were used to modify the M-K model.The forming limit model of GH4169 alloy sheet was modified based on the constitutive equation of GH4169 alloy sheet and the experimental results were predicted.The results show that the prediction accuracy of the modified GH4169 alloy sheet forming limit model is better than that of the macro forming limit prediction model.(3)Study on mesoscopic microbulging process of GH4169 alloy sheetThe micro-bulging experiments of GH4169 nickel-based superalloy sheet were carried out to analyze the effects of grain size and ???/?? phase content on the thickness reduction,maximum bulging depth and maximum bulging load of the bulging parts.The results show that the maximum thickness of bulging parts decreases with the increase of grain size,and increases when grain size increases to a certain extent.The grain size increases gradually,the maximum bulging depth decreases first and then increases,and the pressure required for forming the same height decreases gradually.