Study Of The Room Temperature Formability Of Al-Cu Alloy Sheet

Resources and environment problems become more and more severe in currentsociety. The automotive lightweighting technology is one of the important ways torealize saving energy and protecting environment, and people pay close attention toaluminum alloy which have a series of excellent properties. Besides the pricefactors, however, the forming property of Al sheet materials at room temperature isgreatly decreased by the serrated yielding phenomenon, which limits their furtherapplication in the automobile field. In this paper, the influence of chemicalcomposition, rolling process and heat treatment process on the microstructure,mechanical property, room temperature formability and the serrated yieldingphenomenon of Al-Cu alloy sheet were investigated. The main conclusions are asfollows:(1) Dispersed phase particles exert a tremendous influence to serrated yieldingphenomenon of Al-Cu alloy, and with increasing the copper content, the serratedyielding phenomenon gradually weaken until disappeared. With increasing coppercontent, the mean stress drop amplitude and mean drop duration is on a decliningcurve, but the mean reloading time gradually increases. Critical strain reaches itsmaximum value when the copper content is5.7%.With increasing copper content, the tensile strength and yield strength ofAl-Cu alloy sheet increase and then decrease, reaching the maximum at5.7%copper content, and meanwhile the limit drawing coefficient and the earing rate areminimum. In summary, the Al-5.7%Cu alloy sheet has the better room temperatureformability.(2) The mean stress drop amplitude, reloading time and mean drop duration ofAl-4.9%Cu alloy sheet appear extreme value point when the total cold processingratio of finished goods is60%, and otherwise they vary little. Critical strain isrelatively large when the total cold processing ratio of finished goods is60%and66.7%.The tensile strength, yield strength and elongation of Al-Cu alloy sheet reachtheir extreme points when the total cold processing ratio of finished goods is60%,while when the total cold processing ratio of finished goods is30%and50%, thecomprehensive mechanical properties are better. With increasing total cold processing ratio of finished goods, the Erichsen number increases and thendecreases, but they are not much different. The favorable total cold processing ratioof finished goods of Al-4.9%Cu alloy sheet is30%or50%.(3) Al-4.9%Cu aged alloy sheet have no serrated yielding phenomenon whenuniaxial tension. The relationship between precipitate and the crystal structure ofmatrix have great effect on properties of Al sheet materials. With increasing agingtemperature, the tensile strength and yield strength increase and then decrease.When the aging temperature is less than or equal to150℃, the tensile strength,yield strength and the elongation are higher than those at aging temperature above150℃. When the aging temperature is110℃, the erichsen number is maximum.Thus for Al-4.9%Cu alloy sheet soluted at500℃for2hours, the favorable agingtemperature and time are150℃and3hours.