Study On Microstructures And Damping Properties Of Three Kind Of Aluminum Alloys

Aluminum alloy used in some special fields need not only excellent mechanicalproperties, but also high damping capability to improve their hidden ability, sensitivity andlife span. This thesis studies the structure and internal-friction properties of three kinds ofAl alloys by microstructure observation, mechanical properties tests and internal-frictionproperties tests.Al-Mg-Mn alloy has wide application in naval vessel because of its highcorrosion-resistance and internal-friction properties. The first part of this thesis studies theeffects of trace Sc, Zr on the microstructure under various state (casting, homogeneousannealing, cold working and annealing), recrystallization processing and the internal-frictionproperties. Following results have been obtained:(1) Trace Sc, Zr(0.21wt.%Sc, 0.15wt.%Zr) can fine the casting microstructure ofAl-6.0Mg-0.5Mn. The Al₃Sc_1-xZr_x particles pin dislocation, grain boundary, and sub-grainboundary strongly. So Al₃Sc_1-xZr_x particles can stabilize the microstructure ofAl-6.0Mg-0.5Mn, and prohibit the alloy's recrystallization.(2) After 54% cold deformation, the Al-6.0Mg-0.5Mn-0.21Sc-0.15Zr alloy has beenannealed at 250℃for 2h. The alloy shows non linearity internal-friction character. Theinternal friction increases with the increase of temperature and decrease of test frequency.This alloy shows a internal-friction peak at 326℃in heating Q^-1-T curve tested underfriquence 1Hz,strain amplitude 4.6×10^-5. This internal-friction peak is induced bydislocation interact with fine precipitation particle Al₃Sc_1-xZr_x, and can be explained by themechanism of dislocation pull-off from the pinned Al₃Sc_1-xZr_x particle.(3) Damping spectrum can be used to design heat treatment parameters. Stronglydeformed Al-6.0Mg-0.5Mn-0.21Sc-0.15Zr alloy (deformation ratio 54%) showsinternal-friction peak at about 430℃, which means occurrence of recrystallization, so fineand uniformly distributed grains are gotten when heated to～450℃at 2℃/min andquenching.Al-Fe-Si alloys as heat-resistance materials used in aero-space craft are also needsome damping capability, the second part of this thesis studies the microstructure andinternal-friction properties of spray—deposited Al-3.3Fe-10.7Si samples, and the relationbetween internal-friction properties and ductility of extruded spray—depositedAl-3.3Fe-10.7Si samples are also studied, the main conclusions are: (1) Spray deposited Al-3.3Fe-10.7Si alloy and its extruded samples appearinternal-friction peak at 60～250℃, this internal-friction peak is introduced by grainboundary relaxation, the Al₁₂Fe₃Si particle and Al-Fe intermetallic compound distributed atgrain boundary block the sliding of grain boundary.(2) When annealed at 360℃, The internal-friction peak height of extrudedAl-3.3Fe-10.7Si alloy begin to fall with the annealing time, but after annealed 500min, theheight of internal-friction peak almost fixed. At the early stage of annealing, Al-Fe-Si orAl-Fe particles which have not been precipitated entirely mainly precipitated at grainboundary, and can fortify pinning function to the sliding of grain boundary.(3) The place of internal-friction peak shows the highest ductility in low-plasticityAl-3.3Fe-10.7Si alloy. The reason of the alloy's ductility enhancement is that grainboundary sliding to deplete the vibration energy at this internal-friction peak place.Al—Zn alloy has superplastic and high damping property, but the effects of So,Zr onthe structure, superplastic and damping property of Al—Zn alloy haven't been reported.The third part of this thesis studies the effects of trace Se,Zr on the structure, superplasticand internal-friction property of Al—Zn eutectoid alloy, and main conclusions are:(1) Trace Sc,Zr (0.55wt.%Sc; 0.25wt.%Zr) can increase Al—78Zn eutectoid alloy'sdamping property greatly within 20～250℃, also, So,Zr can stabilize Al—Zn eutectoidalloy's damping property at room temperature, reduce the height of grain boundaryinternal-friction, and decrease the Al—Zn alloy's internal-friction peak about 20K. Al₃ (Sc,Zr) particles can pin grain boundary strongly to block grain boundary sliding and migration, which can reduce the height of grain boundary internal-friction peak. With longer annealingtime, Al—Zn alloy's grain does not coarsen nearly, which can improve the stabilization ofinternal-friction properties at room temperature.(2) The grain boundary internal-friction peak activation energy of Al—Zn eutectoidalloy is 104 kJ/mol. This is nearly equal to Al grain boundary self-diffusion activationenergy which is 101 kJ/mol. The temperature of grain boundary internal-friction peak(499K) is the same as the temperature with largest superplastic. So the Al—Zn eutectoidalloy's superplastic deformation and grain boundary internal-friction peak are all mainlycaused by the grain boundary sliding of Al diffusion.