Studies On The Preparation And Damping Capacities Of Fly-Ash Cenospheres/AZ91D Mg Alloy Composites

Magnesium(Mg)and its alloys have broad application prospects in aerospace,transportation and elecronics industries owing to their low density,high specific strength,excellent machinability and superior damping capacity.Many engineering structure applications produced substantial dynamic vibrations during their normal operation,which highlights increasingly the hazards of vibration and noise.As structural materials,Mg alloys have gained an increasing attention due to their ability in noise reduction and vibration attenuation.However,relatively inferior hardness and strength of Mg alloys have limited their further utilization in structural applications.Mg-matrix composites are promising materials which can not only improve the mechanical properties of Mg alloy but also eliminate vibration and noise.In this study,using the fly-ash cenospheres(FAC)as reinforcement,the FAC/AZ91D Mg alloy composites,ball-milled FAC/AZ91D Mg alloy composites and Mg₂Si/AZ91D Mg alloy compo sites were fabricated by the method of stirring-melt casting.The phase composition of Mg alloy composites was analyzed using XRD and EDS.The microstructure evolution of Mg alloy composites after adding FAC particles was observed using OM and SEM.The effect of solution treatment on the microstructure and properties of Mg₂Si/AZ91D Mg alloy composites was studied.The damping capacities of the three AZ91D Mg alloy composites were studied with dynamic mechanical analyzer(DMA),the damping mechanisms of AZ91D Mg alloy composites were discussed.Finally,the thermal stress relaxation in AZ91D Mg al oy composites was studied.Firstly,the influences of the mass fraction and particle size of FAC on the microstructure and damping capacity of FAC/AZ91D Mg alloy co mposites were studied.The results show that the chemical reaction occurred between FAC and AZ91D Mg alloy and formed two new phases of Mg₂Si and Mg O,while the grain of Mg alloy matrix composites reinforced FAC was more refined than unreinforced AZ91D Mg alloy.With the increase of FAC mass fraction,the internal coarse dendrites in the FAC/AZ91D Mg alloy composites gradually disappeared,and the FAC distribution was more uneven and agglomeration increased.With the increase of FAC particle size,the grain size of the FAC/AZ91D Mg alloy composites becomes coarse.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,FAC/AZ91D Mg alloy composite with 10 wt.%mass fraction and particle size 146?m of FAC has superior damping capacity in the tested specimens,while at higher temperature,the composite with lower FAC mass fraction has a better damping capacity.Secondly,the influences of the particle size of ball-milled FAC on the microstructure and damping capacity of ball-milled FAC/AZ91D Mg alloy composites were studied.The results show that with the decrease of FAC particle size,the more refine for microstructure and more even with no aggregation for FAC distribution of ball-milled FAC/AZ91D Mg alloy composites.The damping capacity of ball-milled FAC/AZ91D Mg alloy composites was superior to that of FAC/AZ91D Mg alloy matrix,and it increases with the increase of the strain amplitude and temperature in the test.At room temperature,the ball-milled FAC/AZ91D Mg alloy composite with particle size 146?m of ball-milled FAC has superior damping capacity in the tested specimens.The ball-milled FAC/AZ91D Mg alloy composite with smal er FAC particle size has a better damping capacity.Thirdly,the influence of FAC mass fraction,stirring time,tested frequency and solution treatment on the microstructure and damping capacity of Mg₂Si/AZ91D Mg alloy composites were studied.The dynamic Young moduli of Mg₂Si/AZ91D Mg alloy composites at high temperature were discussed.The results show that Mg₂Si/AZ91D Mg alloy composites mainly consist of?-Mg,?-Mg₁₇Al₁₂and Mg₂Si.With the increase of FAC mass fraction,the grain of Mg₂Si/AZ91D Mg alloy composites becomes more refine.Mg₂Si phase mrphology transforms from the block to crosswise and polygon.And with the increase of stirring time,Mg₂Si phase mrphology transforms from the coarse block to multi-angle small block.The damping capacity of Mg₂Si/AZ91D Mg alloy composites increases with the increase of the strain amplitude and temperature in the test.At room temperature,Mg₂Si/AZ91D Mg alloy composite with 10 wt.%mass fraction of FAC and 6 min stirring time has superior damping capacity in the tested specimens.Mg₂Si/AZ91D Mg alloy composites have higher damping capacity at lower test frequency.At room and higher temperature,Mg₂Si/AZ91D Mg alloy composite after solution treatment has higher damping capacity than those of as-cast state.The damping capacity-temperature curves of Mg₂Si/AZ91D Mg alloy composites exhibit a damping peak at 100 ^oC-200 ^oC,and the peak has obvious thermal activation characteristics.At the same time of increasing the damping capacities of Mg₂Si/AZ91D Mg alloy composites,the loss of stiffness is caused.The dynamic Young's moduli of Mg₂Si/AZ91D Mg alloy composites decrease with the increasing temperature.Finally,the thermal relaxation of FAC reinforced AZ91D Mg alloy composites was studied.By using the viscous friction and solid friction model,the relationships between the transient damping value and T/?of the AZ91D Mg alloy and FAC/AZ91D Mg alloy composites at 300 ^oC have been obtained,and the parametersC_K and C_?0as a function of the temperature were fitted according to the model.