Study On The Structure And Properties Of Mg-9Y-1MM-1Zn-0.6Zr Alloy

With the continuous progress of science and technology,the development of space shuttle,high-speed missiles and civilian vehicles is advancing rapidly.How to reduce the vibration hazards generated during the use of high-speed operating equipment has also gradually become a research hotspot.Magnesium alloys have excellent damping properties among metallic materials and become the most promising vibration damping materials.However,the strengthening theory of magnesium alloys and the dislocation damping mechanism have conflicting relationships at present,while the strength of magnesium alloys decreases significantly at high temperatures,which limits the further expansion of magnesium alloy applications,therefore,how to achieve a synergistic balance between the two aspects is one of the hot spots of current research.To solve the above problems,the thesis designed Mg-9Y-1MM-1Zn-0.6Zr alloy.Microstructures of as-cast,as-homogenized,as-extruded and peak-aged alloys were investigated.The room-temperature and high-temperature mechanical properties and damping capacity of the alloys were analyzed and the internal relations between microstructure and properties were established,which provided reliable experimental data and theoretical support for the development of high-strength and high-damping magnesium alloys serving in high-temperature environments.The as-cast WE91B alloy strengthening phases included Mg24Y5,Mg3MM and Mg12YZn phases(LPSO phases).The optimum homogenization regime for alloy was 520℃-48 h.And the Mg24Y5 phase re-dissolved,Mg3MM phase transformed to Mg12MM phase,and the 18R-LPSO phase transformed into 14H-LPSO phase after homogenization.The as-cast WE91B alloy had low comprehensive mechanical properties and exhibited typical characteristics of intergranular brittle fracture;After homogenization,the tensile strength of the alloy increased to 210 MPa due to the re-dissolution of the eutectic organization,and the fracture mode was mix-fracture of transcrystalline fracture and intergranular fracture.Dynamic recrystallization occurred after the alloy extrusion,and the Mg-MM phases and LPSO phase were distributed within the alloy,and stacking faults appeared within the grains.The tensile strength,yield strength and elongation of as-extruded WE91B alloy were 333 MPa,273 MPa and 10.0%,respectively.After peak aging treatment at 200℃-84 h,a large amount of β’ phase precipitated inside the alloy and the tensile strength reached 425 MPa.Meanwhile,the peak-aged WE91B alloy showed excellent high-temperature mechanical properties with a tensile strength of 380 MPa at 250℃.The fracture of asextruded alloy showed a large number of dimples and exhibits mixed tough-brittle fracture.After peak aging,the number of dimples in the fracture of the alloy decreased.The variation of damping capacity with strain amplitude at room temperature for WE91B alloys in different states could be approximated by the G-L dislocation pinning theory.The alloy damping capacity gradually increased with the temperature.The peak-aged WE91B alloy had the Q-1 value of 0.16 at 250℃ and exhibited excellent damping properties.The damping mechanism of the alloy at room temperatures was mainly dislocation damping mechanism,and at high temperature were dislocation damping mechanism and the interfacial damping mechanism.The peak-aged WE91B alloy can achieve a synergistic balance of strength and damping capacity at high temperature.