Research On Damping And Shape Memory Effect Of MnCu Alloys Fabricated By Selective Laser Melting

MnCu alloy is an excellent high damping alloy.Nowaday,MnCu alloy is usually fabricated by conventional casting and forging technologies,but it’s rather difficult to manufacture the MnCu alloy parts with high manganese contents or complex shapes.Selective laser melting(SLM)technology can directly realize the manufacture of refractory,high-strength,high-hard,difficult-to-machine materials and almost any complex structural metal parts,which is an advanced method to solve the manufacturing problem of MnCu alloys.Therefore,based on Mn and Cu mixed elemental powders,SLM technology was applied to manufacture MnCu alloys in this study.The formability,microstructural features,mechanical properties,damping properties and shape memory effect of the fabricated MnCu alloys were investigated.Also,the heat treatments were developed to regulate and control the microstructure and properties.The main results are summarized as follows:(1)SLM technology can realize manufacturing MnCu alloys with high density.The highest density of the SLMed MnCu alloys can reach 99.8%.The pores are the main metallurgical defect in the SLMed MnCu alloys.With the increase of the Mn content from60% to 85%,the SLM processing window becomes narrower and the forming quality becomes worse.The microstructure of the SLMed MnCu alloy is mainly composed of single phase γ-MnCu solid solution,and the center of grains are rich in Mn element and the boundary of grains are rich in Cu element.Only the 85Mn15Cu alloy can undergo the Fcc-Fct martensitic transformation at room temperature,but the MnCu alloys with medium manganese can achieve the Fcc-Fct martensitic transformation through subsequent aging treatment.But the second phase of α-Mn is precipitated during aging treatment.(2)with the increase of the Mn content,the tensile properties of SLMed MnCu alloysbecome worse.The elongation of MnCu alloy will become poor after aging heat treatment.After solution heat treatment,MnCu alloy has the highest elongation but the strength is poor.MnCu alloy has better comprehensive tensile properties after solid solution+aging heat treatments.The values of tensile strength,yield strength and elongation of the SLMed70Mn30Cu alloy followed by solution and aging heat treatment at 900 ℃×1 h+400 ℃×2h can reach 622 MPa,379 MPa,and 19.5% respectively,which are beyond the stangard of casting.(3)with the increase of the Mn content,the damping properties of the SLMed MnCu alloy increase.But only the 85Mn15Cu alloy reaches the level of high damping.Heat treatment can significantly improve the damping properties of MnCu alloys,which can reach the level of high damping.The optimized heat treatment regime for the SLMed60Mn40 Cu alloy is solid solution at 900 ℃ for 1 hour and aging at 430 ℃ for 2 hours with a Tanδ of 0.050.The optimized heat treatment regime for the SLMed 70Mn30Cu alloy is solid solution at 900 ℃ for 1 hour and aging at 430 ℃ for 1 hour with a Tanδ of0.071.And the optimized heat treatment regime for the SLMed 85Mn15Cu alloy is solid solution at 900 ℃ for 1 hour and aging at 400 ℃ for 2 hours with a Tanδ of 0.036.(4)Different from the MnCu alloys with medium manganese,the SLMed 85Mn15Cu alloy showes a shape memory effect at room temperature with the maximum one-way recoverable strain of 1.12% and the maximum two-way recoverable strain of 0.49%,which are beyond the standard of casting.Heat treatment can also improve the shape memory effect of the MnCu alloy,but the shape memory effect of the 60Mn40Cu alloy is still below the standard of casting.However,the shape memory effect of 70Mn30Cu and85Mn15Cu alloys can rearch the standards of casting after solid solution+aging heat treatment.In general,the SLMed 70Mn30Cu alloy followed by solution and aging heat treatment at 900 ℃×1 h+400 ℃×2 h can realize a good comprehensive properties of mechanics,damping and shape memory effect.The tensile strength,yield strength andelongation can reach 622 MPa,379 MPa and 19.5%,respectively.Tanδ can reach 0.054 at an amplitude of 100 μm.The maximum one-way recoverable strain and the maximum two-way recoverable strain can reach 1.25% and 0.55%,respectively.