| At present,the 6000 series Aluminum Alloy is one of the hotspot of research and application in lightweight automobile field.the application in the proportion of cars is on the rise because they can well meet the requirements of the car on the shell,especially for the sheet after heat treatment(such as T4,T6,T8X).But the preparation process is complicated and verbose.They usually producted though casting,sawing,milling,homogenizing,hot rolling and cold rolling(including intermediate annealing).In this paper,6016 aluminum alloy sheet was prepared by twin roll casting and subsequent heat treatment was studied.First two kinds of sheet were successfully prepared by twin roll-casting with or without electromagnetic field in the laboratory.The microstructure and tensile properties of the two sheet were compared and analyzed to confirm the effect of the electromagnetic field.Then cold roll the sheet roll-casting with electromagnetic field to0.9~1.2mm after annealing.Next the mechanical properties of T6 state after solid solution quenching at different temperatures and the effect of different pre-aging processes on the hardening properties of the paint were investigated.The target is to develop a suitable heat treatment process to make the 6016 cast rolled sheet meet the requirements of the enterprise in terms of stamping formability and baking hardening performance after processing.Based on the experimental conditions conclusions are as follows:(1)There is an obvious segregation zone in the metallographic structure of the 6016 aluminum alloy cast rolling sheet without electromagnetic field,and the main alloying elements Mg and Si enrichment at the grain boundaries,causing seriously impact on the various performances of the board.After the electromagnetic field was applied,the intermediate segregation of cast rolled plates decreases or even disappears.Mg and Sidistribute more dispersed in the matrix,which effectively improves the microstructure and properties.(2)Compared with conventional roll casting sheet,the grain size of the twin roll-casting sheet was refined,and the grain boundary became more regular,otherwise the coarse dendrites were reduced and the zone of equiaxial crystals was broadened,second phase particle distribution was more uniform and the mechanical properties were enhanced.what is more,comparing the tensile properties of conventional twin roll-casting sheet and electromagnetic sheet,we can know that the tensile properties of electromagnetic casting sheet in three directions of TD,45 ° and RD have little difference,which is more conducive to further rolling process.(3)The twin roll-casting sheet was subjected to different quenching treatment,The suitable solution treatment process of the sample was 550°C×30min,referring to metallographic structure,scanning microstructure,fracture analysis,and T6 state mechanical property test.The mechanical properties after T6 treatment reached Rm: 350 MPa,Rp: 290 MPa,and A: 15%.(4)It can be seen from the natural aging hardening curve of the 6016 twin roll-casting sheet that the hardness of the cast sheet gradually increased during the natural aging process,from the quenched state of 62 Hv to 89 Hv 7 days later,which is not conducive to the stamping process.Besides the paint hardening effect was not satisfactory and could not meet the requirements of the manufacturers.Therefore,proper pretreatment was required to improve the sheet forming performance and the baking hardening performance.(5)Comparing the mechanical properties of different pre-aging process,the best pre-aging process was 160°C×5min,after which the properties reach Rm: 242 MPa,Rp:118MPa and A: 26.6%.Otherwise it could be seen from the DSC curve that the formation of the ? " precipitation peak was forward,what means the ?" phase was more easily precipitated and the performance after the paint baking was greatly improved. |
PDF Full Text Request