Effect Of Rolling Geometry On The Inhomogeneity Of Microstructure,Texture And Hardness In Cold Rolled And Annealed Aluminium Alloys AA1050 And AlSi10Mg

During cold rolling,the texture of the metal may become inhomogeneous and vary through the sample thickness,due to shearing in the roll gap.The roll-gap geometry is the dominant factor in determining the strength of shear deformation.Although there have been numerous studies showing that the rolling geometry causes inhomogeneities and through-thickness texture variations of the plates after deformation,it has not yet to be systematically investigated how this inhomogeneity change after subsequent annealing.The effect of this inhomogeneity on the mechanical properties is also not yet clear,and it is also worth exploring whether materials with a heterogeneous microstructure can be obtained by modulating the rolling geometry.In this thesis,the effects of rolling geometry on the microstructure,texture and mechanical properties of commercial pure aluminium AA1050 prepared by conventional methods and Al Si10 Mg manufactured by selective laser melting(SLM)were investigated after cold rolling and annealing of the samples.The commercial pure aluminium AA1050 cold rolled with low,medium and high draughts to 50% and 80% reduction in thickness.Through-thickness variation of the microstructure,texture,and mechanical properties of the plates were studied by electron backscatter diffraction(EBSD),X-ray diffraction(XRD)and microhardness.The recrystallization kinetics and the fully recrystallized state of commercial pure aluminium AA1050 were also investigated.For the Al Si10 Mg manufactured by SLM,through-thickness microstructure,texture,second particles and hardness variations after printing,cold rolling and annealing were investigated by scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),energy dispersive spectroscopy(EDS)and microhardness.The major results of this work can be summarized as follows.(1)While the rolling geometry was found to strongly affect the deformation texture and significant through-thickness texture gradients were observed for rolling with small and large draughts,the results showed that the change in rolling geometry did not create through-thickness gradients in neither microstructure and nor hardness.(2)Even slight deviations from homogeneous rolling do produce through-thickness texture inhomogeneities in the commercial pure aluminium AA1050 plates,but these inhomogeneities have little effect on the recrystallization kinetics.After complete recrystallization,through-thickness texture inhomogeneities still are present,but weaker compared to the rolled state.(3)SLM-manufactured Al Si10 Mg cold rolled with low draught to 10% reduction in the thickness resulted in a significant deformation zone in the surface layer at a depth of approximately 430 ?m and a bit strong Goss texture in this region,while the center region away from the surface layer showed no significant change in deformation microstructure and texture as compared to the printed state.10% cold rolling process resulted in an increase in the microhardness of the Al Si10 Mg manufactured by SLM from 130 HV to 151 HV.(4)After a two-stage heat treatment of SLM manufactured Al Si10 Mg cold rolled10%,annealed at 525°C for 4 h water-quenched and finally annealed at 165°C for 7 h,abnormal grain growth and consequently a strong {124}<0 2 1> texture developed in the surface layer.The microstructure and texture at the center layer is not significantly different from that of the printed and annealed sample.The hardness of the cold rolled sample after heat treatment was maintained at 103 HV,which is a 47% increase in hardness compared to the sample annealed directly after printing.