Regulating Microstructure And Properties Of Magnesium Aluminum Alloys By Coupling Aging And Deformation

This work aims to regulate the microstructure and properties of Mg-Al alloys by coupling aging and twinning deformation.AZ80 and AZ91 magnesium-aluminum alloys were used as the model materials.Various samples were obtained by combining heat treatment and different deformation processes.Electron backscatter diffraction(EBSD),scanning electron microscope(SEM)and transmission electron microscope(TEM)techniques were used to study the influences of the heat treatment and various deformation processes on the microstructure,texture and mechanical properties,and their underlying mechanisms.(1)The effects of coupling pre-aging treatment and rolling on the microstructure evolution and mechanical properties of AZ80 alloys were investigated.Pre-aging at 200^oC for 30h(the peak-aging condition),followed by rolling at 200^oC to different reductions(10-40%)were carried out.The experimental results show that coupling pre-aging and rolling can significantly enhance the mechanical properties of AZ80 alloys.Particularly,the sample subjected to pre-aging and rolling by 30%reduction exhibits the optimal yield strength(350 MPa for tension and 280 MPa for compression).The orientation relationship(OR)between Mg₁₇Al₁₂ precipitates and Mg lattice was also analyzed by transmission electron microscope(TEM).Two new ORs were revealed in the AZ80 alloy subjected to pre-aging and side-rolling,which are described as[11-20]?//[-111]?,(0002)?5^ofrom(211)?and(0001)?//(3-11)?,[10-10]?//[011]?.(2)The effects of peak-aging and torsion deformation on the microstructure and mechanical properties of an extruded AZ91 alloy were investigated.Comprehensive microstructure analyses were performed on the samples subjected to different deformation and peak-aging routes.The experimental results show that reversing the sequence of the applied deformation and peak-aging treatment on the AZ91 sample significantly influences its mechanical properties.The sample subjected to peak-aging and subsequent torsion deformation has higher yield strength compared to the sample subjected to pre-torsion deformation and subsequent aging treatment,meaning that it is more effective to strengthen AZ91 alloys by applying peak-aging prior to torsion deformation.Some precipitates exhibit irregular shapes due to the interaction with twin boundaries.The precipitates found in twins have the OR of(0001)_t 6^o from(-11-2)?and[2-1-10]_t//[-111]?with the?-Mg lattice.(3)Aging prior to extrusion was used to regulate the microstructure and mechanical properties of AZ91 alloys were investigated.The results showed that pre-aging can induce numerous precipitates in Mg matrix to refine the recrystallized microstructure during hot extrusion of AZ91 alloys.After extrusion,most precipitates distributed at grain boundaries,suppressing grain growth.Thus,coupling pre-aging and hot extrusion can effectively enhance the yield strength of AZ91 alloys and maintain considerable plasticity(>15%)simultaneously.By contrast,the improvement in mechanical properties is not so effective by direct extrusion and subsequent heat treatment.Although the subsequent aging(T6 treatment)can induce dense precipitates inside grains,generating strong precipitation hardening,it badly reduce the tensile ductility (to 6.3%).