Studies On The Microstructure And Damping Capacity Of Fly Ash Cenosphere/AZ91D Magnesium Alloy Composites

With the development of modern industry,the harm caused by vibration and noise is more and more outstanding.The development and applications of suitable high damping and high-performance Mg alloys are considered as an effective way to eliminate unwanted vibrations and acoustic noises.In this paper,the fly ash cenosphere/AZ91D?FAC/AZ91D?magnesium alloy composites were prepared by the method of Stirring-Melt Casting.The microstructure evolution of Mg alloy composites after FAC particles were added was observed using OM and SEM.The phase composition of Mg alloy composites was analyzed using XRD and EDS.The effects of solid solution and semi-solid isothermal heat treatment on the microstructure and properties of Mg alloy composites were studied.The damping behaviors of as-cast and heat treatment state FAC/AZ91D Mg alloy composites were analyzed with dynamic mechanical thermal analyzer?DMA?.Finally,the damping mechanisms of FAC/AZ91D Mg alloy composites were discussed.The effects of the content and particle size of FAC on the microstructure and damping capacity of as-cast Mg alloy composites were studied.The results show that the interfacial reaction occurred between FAC and AZ91D Mg alloy and formed two new phases of Mg₂Si and MgO,while the grain of Mg alloy matrix was refined.The damping capacity of FAC/AZ91D Mg alloy composites was superior to that of AZ91D Mg alloy matrix,and it increases with the increase of the temperature and strain amplitude in the test.At room temperature,Mg alloy composites with high content and large particle size of FAC have a better damping capacity.The damping-temperature curves of the composites exhibit a damping peak at approximately 150?,and its mechanism is the dislocation induced damping.The interfaces between Mg alloy matrix and FAC significantly affect the damping capacity of the composites.If the reaction product of Mg₂Si particles wraps the wall of FAC without uniform distribution,the interface damping will decrease,resulting in the deterioration of the damping capacity of the composites.The effects of the solid solution time on the microstructure and properties of FAC/AZ91D Mg alloy composites were studied after heat treatment.After solution treatment,?phase(Mg₁₇Al₁₂ phase)was decomposed,and a large number of Al atoms were dissolved into the matrix,thereafter the grain boundary became more distinguishable,and the fine Mg-Al phase was precipitated out eventually.The solid solution treatment can improve the quasi-static compressive properties of the composites,and the quasi-static compressive properties of the composites increase with the increase of the solid solution treatment time.The compression fracture of the composites belongs to the brittle fracture of cleavage fracture.At room temperature,the damping capacity of the composites with shorter solid solution time is better,while the composites with longer solid solution time show a better damping capacity at high temperature.After the semi-solid isothermal treatment of FAC/AZ91D Mg alloy composites,the effects of the semi-solid heat treatment on the microstructure and properties of the composites were studied.The results show that with the increase of the time and temperature of the semi-solid isothermal heat treatment,the grain size grew gradually,then the grain boundaries became more and more distinguishable,and the small liquid pool became large in the grain,finally the size and shape factor of Mg₂Si particle increased.The semi-solid isothermal heat treatment improves the quasi-static compression performance of FAC/AZ91D Mg alloy composites.At room temperature,the composites with low heat treatment temperature show a better damping capacity,while the composites with high heat treatment temperature have a higher damping capacity at high temperature.After heat treatment,the damping capacity of the composites with different FAC content was significantly different from that of as-cast composites.It can be found that the damping of the composites mainly originate from the interface damping,the dislocation damping and the grain boundary damping through the analysis of the damping behaviors of FAC/AZ91D magnesium alloy composites in as-cast and heat treatment state.The damping of the composites depends on the number and the mobility of the interfaces,dislocations and grain boundaries.With the increase of the applied stress or temperature,interfaces,dislocations and grain boundaries start to move in turn,thus damping capacity of FAC/AZ91D Mg alloy composites is constantly improved.