Study On Recrystallization Mechanism During Annealing And Formability Of AA6014 Aluminum Alloy

With the wide using of 6xxx aluminum alloy on forming automotive,many researches have been carried on 6xxx aluminum.6xxx sheet used for automotive outer panels require a microstructure that will produce a good combination of strength and formability.Researches on its annealing process and recrystallization are few.Annealing process was studied in this research.Relationships between the mechanical properties,microstructure and texture were also analysed.Center?C?and edge?E?materials from AA6014 sheet was annealed between200^oC and 300^oC with 50°C/h heating rate to studied the recrystallization behavior.A series of C samples were annealed at 200^oC,300^oC,400^oC,500^oC,560^oC with heating rate between 50°C/h and 1.26×10⁶°C/h.HV,grain structure,texture and second phase of samples were characterized by hardness,OP,XRD,EBSD,SEM and TEM.Tensile results from 3 different test directions were used as input to VPSC model to predict r-values and FLD in this study.The results are as follows:?1?The recrystallization behavior of material C and E were different.E recrystallization started at a lower temperature than C,but the recrystallization did not make much difference.The recrystallization mechanisms of the two materials were different during annealing with slow tempering,which leads to the strong preference orientation?Cube?of E materials,and grains were more flat and larger than C material.?2?Recrystallization mechanism and grain size were affected by heating rate.Cube texture oriented nucleation and growth and PSN played a leading role in recrystallization nucleation mechanism of C material at slow heating rate.Rapid heating rate had finer grain size.?3?Mg₂Si precipitates and hardness were effaced by the heating rate.Change tendency of the Mg₂Si content in slow heating rate was stronger than that of rapid heating rate.The hardness of recrystallized grain was controlled by recrystallization softening,the second phase strengthening and the solid solution strengthening.?4?Mg₂Si precipitates with a size less than 1?m can inhibit recrystallization,while Mg2Si with larger than 1?m can promote nucleation by PSN.PSN,grain boundary pinning and grain boundary migration together affected the grain growth.?5?Texture correlated strongly with the differences in r-values and FLD.45^o direction showed a lowest r-value because of the strong Cube texture.VPSC model showed a favorable prediction on r-values.