Effect Of Aging Treatment On Mechanical Properties And Strain Inhomogeneity Of Al-1Mg-0.3Si Alloys

Under the requirements of automobile lightweight,6XXX series aluminum alloys have been widely used due to their excellent comprehensive performance.Aging is one of the most common strengthening mechanisms for Al-Mg-Si alloys.However,the aging treatment will reduce the plasticity while increasing the strength of the alloy,which limits its application to some structural parts that have high requirements on strength and plasticity.Therefore,studying the effect of aging on the mechanical properties and deformation mechanism of aluminum alloy is of great significance to improve the mechanical properties of the alloy.In this paper,quasi-2D polycrystalline samples were cut from the Al-1Mg-0.3Si columnar structure obtained by directional solidification.With the help of micro hardness tester,tensile machine,electron backscatter diffraction,scanning electron microscope,and other equipment,digital image correlation method(DIC)is used to characterize the surface strain fields of alloys with different aging condition at different strain levels.The influence of aging conditions on the strain heterogeneity is studied in combination with grain orientation.The slip trace analysis method is used to determine the partially activated slip system.With reasonable heat treatment processes,the plasticity of the alloy can be improved while maintaining or even increasing the strength: Yield strength and elongation of 175°C-9h state respectively is 158 MPa and 14.5%;Yield strength and elongation of 225°C-0.5h state respectively is 155 MPa and 10%;Yield strength and elongation of 175°C-16 h state respectively is 192 MPa and 8%;Yield strength and elongation of 225°C-1h state respectively is 196 MPa and 5%.175°C-9h state comparing with 225°C-0.5h state,the yield strength is similar but the elongation increased by 31%;175°C-16 h state comparing with 225°C-0.5h state,the yield strength is similar but the elongation increased by 44.9%.This paper focuses on the analysis of the strain distribution of the above two groups of comparative samples and solid solution samples.The DIC results show that obvious deformation bands are observed in all samples and the maximum plastic deformation is preferentially generated in this grain.This is because under the premise that the grain orientation is similar,the less the grains are restricted by the grain boundaries,the smaller the resistance of dislocation movement,and the more likely to be plastic deformation.The strain distribution and evolution of the solid solution sample are more uniform than that of the aging samples.On the one hand,the color distribution of the strain map of the solid solution sample is more uniform than that of the aging samples.On the other hand,the global strain increment is more uniform than the aging samples.Compared with 225°C-0.5h and 225°C-1h,the better plasticity of 175°C-9h and 175°C-16 h may be related to its large deformation area.The 225°C-0.5h and 225°C-1h samples with poor plasticity have more discrete distribution of large deformation regions,while the 175°C-9h and 175°C-16 h samples with better plasticity have more continuous deformation regions and can bear more more plastic deformation.The DIC method can be combined with slip traces to analyze the slip system activated in the grain.The parallel strain lines and deformation bands observed in the DIC strain distribution pattern can be regarded as the actual slip trace direction,and then combined with the theoretical slip trace obtained by Euler angle,the corresponding activated slip system can be determined.According to the activated slip system and the deformation coordination factor between the grains,the deformation coordination between the grains can be analyzed and the activation sequence of the slip system can be determined.