| Aluminium alloys are widely used for their excellent properties such as low density,high strength and corrosion resistance.High damping performance means that the material has a good vibration and noise reduction function.The application of highly damped structural materials can reduce the design of vibration damping structures,which can effectively save costs and reduce weight.However,the current low damping properties of commercial aluminium alloys limit their application in the field of vibration and noise reduction.The use of a highly damped reinforcing phase to prepare aluminium matrix composites can effectively improve the damping properties of aluminium alloys.NiTi alloy has excellent intrinsic damping and phase-transition damping characteristics.In this paper,NiTip/1060Al,NiTip/6061Al and NiTip/7075Al composites were prepared by Friction Stir Processing(FSP)using NiTi particles in different ageing states as the reinforcing phase and three commercial aluminium alloys,1060Al,6061Al-T6 and 7075Al-T6,as the matrix,and their microstructure,phase-transition behaviour,tensile properties and damping behaviour were investigated.The results show that the NiTi particles are uniformly distributed in the aluminium matrix and the interface with the aluminium matrix is well bonded,with no reaction products generated at the interface and only slight diffusion of elements.FSP is effective in refining the grain size of the aluminium matrix.Composites all exhibit phase-transition characteristics similar to those of their NiTi-reinforced particles.The aging treatment did not change the phase-transition temperature and phase-transition behavior of the NiTip/6061Al and NiTip/7075Al composites,but the T6 treatment changed both the phase-transition temperature and phase-transition behavior of the composites.The aging state of NiTi particles has almost no effect on the tensile properties of the composites.The tensile strengths of NiTip/1060Al and NiTip/6061Al composites are 11.1%and 16.1%higher than FSP-1060Al and FSP-6061Al alloys,respectively,and the strength of NiTip/7075Al composite is not much different from FSP-7075Al alloy.Aging and T6 treatment of NiTip/6061Al and NiTip/7075Al composites can significantly improve their strength.The phase-transition internal friction peaks caused by the phase boundary motion in the NiTi particles appear in all the composites,and the change in the aging state of the NiTi particles changes the temperature of the phase-transition internal friction peaks in their composites.Peak internal friction of as-NiTip/1060Al composites reached0.012 when cooled down to-52 ~oC,which represents a 200%increase in internal friction value compared to FSP-1060Al alloy under the same conditions.Peak internal friction of 0.01 for the as-NiTip/6061Al-T6 composite when warmed to 30 ~oC,which is 135%higher than the internal friction value of the FSP-6061Al alloy.During the cooling process,the 350 ~oC-NiTip/7075Al composite has a high damping plateau related to R phase in the range of-43 ~oC to-100 ~oC,and the internal friction value in the damping plateau interval is stable at 0.0078.The aging treatment hardly affected the damping behavior of NiTip/6061Al and NiTip/7075Al composites.The T6treatment will significantly change the damping behavior of the composites,causing the change of the phas-transition internal friction peak.The use of NiTi particles with different aging states as reinforcements can not only effectively improve the damping properties of the composites,but also regulate the phase-transition damping temperature region of the composites according to the actual needs,which is expected to realize the functionalization and customization of high damping aluminum matrix composites. |
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