Mechanical And Damping Properties Of Fine-Grained Al-Mg And Al-Mg-Sc Alloys

Al-Mg alloys have been widely used in aerospace,marine transportation and other fields due to its good specific strength,processing formability,corrosion resistance and weldability.Al-Mg alloys are typical non-aging strengthening alloys.Its strength can be improved by increasing dislocations and microalloying,but this often weakens the plasticity of the alloys.Studies have shown that aluminum alloys with fine equiaxed crystal structures usually exhibit good plasticity.In addition,the excellent grain boundary slipping ability of fine grain（FG）structure can effectively improve the damping performance of Al-Mg alloys,thus expanding the application range of the alloys.In this paper,the mechanical and damping properties of fine-grained Al-Mg and Al-Mg-Sc alloys with different Mg contents are explored,and the grain boundaries（GBs）slip behavior is studied.The deformation behavior of the above alloys at room temperature and high temperature was analyzed,which provides a reference for the development of Al-Mg alloys with high plasticity,high strength and excellent damping properties.In this paper,Al-Mg and Al-Mg-Sc alloys with different Mg contents were prepared by self-melting and casting.The alloys were subjected to friction stir processing（FSP）and subsequent heat treatment process to obtain fine-grained structural alloys with different grain size ranges.The microstructure,mechanical properties and damping properties of fine-grained Al-Mg and Al-Mg-Sc alloys were studied by means of optical microscope,transmission electron microscope,electron backscatter diffraction,universal mechanical testing machine and dynamic thermomechanical analyzer.The results show that among the fine-grained（FG）,medium-grained（MG）and coarse-grained（CG）Al-Mg alloys prepared by FSP with different heat inputs,the FG-structured Al-6.9Mg alloy exhibits higher strength than other Al-Mg alloys with composition and state due to higher dislocation and solid solution strengthening effects.The plasticity of Al-Mg alloys with FG structure also increases with the increase of Mg content and the decrease of grain size.The high content of Mg solid solution atoms and fine equiaxed grains can increase the work hardening rate and improve the stress distribution of Al-Mg alloys during tensile process.Therefore,the yield strength,tensile strength,uniform elongation and total elongation of fine-grained Al-6.9Mg alloy can reach 188 MPa,341 MPa,30%and 35%,respectively.The Al₃Sc phase can further refine the grains of Al-Mg-Sc alloys after FSP.The increase of Mg content and grain refinement improve the strength and high temperature damping value of Al-Mg-Sc alloys.The FG structure Al-6.9Mg-0.25Sc alloy has higher work hardening ability and better plasticity.The grain boundary pinning effect of Al₃Sc phase improves the damping stability of FSP Al-Mg-Sc alloys.The unannealed FG structure Al-6.9Mg-0.25Sc alloy exhibits the best comprehensive properties,including excellent mechanical properties,high damping value and high damping stability.In addition,the solution treatment does not destroy the fine equiaxed crystal structure of the Al-Mg-Sc alloys in the FSP state,and eliminates the segregation of Mg element and dislocation.Therefore,the alloys can be used to study the low-temperature Hall-Petch relationship and high-temperature grain boundary slip behavior of Al-Mg-based alloys.The results show that the k value in the Hall-Petch equation of Al-Mg-based alloys increases with the increase of Mg content,and the relationship between k value and Mg content is given in this paper.Grain refinement and high Mg content can not only reduce the GBs slipping temperature of Al-Mg-Sc alloys during high temperature deformation,but also improve its high temperature GBs slipping capacity.