The Control Mechanism Of The Microstructure Via Novel Thermo-mechanical Treatment In Al-Cu-Mg Alloy

In response to the demand for high-performance Al-Cu-Mg alloys in aerospace,a novel thermo-mechanical treatment(NTMT)process based on solution treatment-hot rolled-quenched process and asymmetric rolling/cyclic strengthening was proposed.The effects of the NTMT on properties and microstructure evolution of Al-Cu-Mg alloys were investigated by room temperature tensile testing,fatigue crack growth(FCG)rate testing,transmission electron microscope(TEM),X-ray diffraction(XRD),scanning electron microscope(SEM),electron backscatter diffraction(EBSD)and three-dimensional atomic probe(3DAP).The main research findings are as follows.(1)The NTMT enables Al-Cu-Mg alloys to obtain a good combination of strength and ductility.The ultimate tensile strength and yield strength of alloys reach up to 528.5 MPa and 477.7 MPa,respectively,which are 9.8% and 27.5% higher than those of the T6 state while maintaining a good elongation.(2)The main reason of the NTMT to improve the strength and toughness of the alloy is the synergistic modulation of co-clusters,dislocation morphology and texture configuration.The co-cluster strengthening plays an important role,and the contribution of co-clusters to the critical resolved shear stress of the alloy can reach 114.0 MPa.(3)The process of controlling the evolution of the microstructure in the alloy via the NTMT is shown below.Defects such as dislocations and vacancies in the oversaturated hot-rolled structure are obtained by solution treatment-hot rolled-quenched process,followed by low-temperature pre-ageing to control the uniform formation of Cu-Mg co-clusters.Lots of dislocations are introduced during asymmetric rolling,and co-clusters interact with defects such as dislocations and vacancies during plastic deformation.The final ageing promotes the further segregation of Cu and Mg atoms.(4)The NTMT can obtain Al alloys with high tensile properties and good FCG resistance.The Cu-Mg co-clusters reduce fatigue damage accumulation by relieving the stress concentration generated by dislocation slip,which is one of the reasons for the lower fatigue crack growth rate of NTMT treated alloys.(5)The regulation of grain orientation by the NTMT is an important mechanism to improve the FCG resistance of alloys.The texture evolution process of NTMT treated alloys includes the formation and transformation of recrystallized textures such as Cube,Goss and P texture,the formation of rolled textures such as Brass,Copper and S texture,and the formation of shear textures such as R-Cube texture.Shear texture and Goss grains reduce the FCG rate by affecting the deflection of fatigue cracks.