Characteristics And Its Regulating Exploration Of Cu-Al-Mn Shape Memory Alloys Fabricated By Additive Manufacturing With Powder Core Wire

Cu-Al system shape memory alloys have become a research hotspot due to their excellent memory properties and thermal stability.The introduction of the Mn element is outstanding in coordinating the contradiction between memory properties and brittleness of Cu-Al system shape memory alloys.At the same time,additive manufacturing of Cu-Al system shape memory alloys is an excellent development direction for Cu-based shape memory alloys.Based on the above considerations,this article selects Cu-Al-Mn shape memory alloy with excellent development potential as the research object;uses arc additive manufacturing with high forming efficiency,high material utilization rate,low cost,and low sensitivity to metal materials as the research method;and selects powder core wire with a"leather powder" damage resistance structure and easy composition control as the additive manufacturing material.The research is around the characteristics and regulation exploration of the Cu-Al-Mn memory alloy produced by additive manufacturing technology with powder core wire,intended to clarify the process,microstructure,and properties characteristics of the Cu-Al-Mn alloy.And on this basis,explore the regulatory effect of the fourth component(Fe element)on Cu-Al-Mn memory alloy.The work can provide a reference for promoting the development of Cu-based shape memory alloy manufacturing with additives.The main research contents and results of this paper are as follows:(1)The process characteristics of Cu-Al-Mn alloy produced by additive manufacturing technology with powder core wire were studied.By analyzing the phase diagram,the Al content of Cu-Al-Mn alloy was designed as 12.5 wt.%.And the Mn content was designed to 1wt.%～5wt.%according to the undetermined oxidation condition.By calculating the material allocation plan of powder cored wire and selecting appropriate powder filling and drawing processes,powder cored wire that meets the experimental requirements were prepared.Moreover,based on the previous research of the research group,the theory of melt deposition forming of powder core wire has been further improved.At the same time,the Simulact-Welding platform was applied to numerically simulate the temperature field of Cu-Al-Mn alloy produced by arc additive manufacturing.The effects of deposition input current I,arc scanning speed v,and interlayer cooling time t on the temperature field of the thin-walled layer under orthogonal experimental parameters were explored while ensuring the melting enough of various components in the wire and minimizing the burning loss of evaporated elements.The optimal experimental parameters under the experimental conditions of this article were obtained(I=140A,v=6mm/s,t=15s).(2)The microstructure characteristics of Cu-12.5Al-xMn(x=1,2,3,4,5)alloy produced by additive manufacturing technology with powder core wire were studied.Research has shown that all five alloys have a eutectoid microstructure(α+γ2)mainly and contain brittleness γ2 phase and γ-Al2O3 phase.And with the increase of Mn content,the asdeposited microstructure of the alloy becomes closer to the eutectoid microstructure,and the brittle γ2 phase gradually decreases.But the γ-Al2O3 phase increase slightly.In the quenched microstructure,β1’ martensite and a small amount of γ1’ martensite are dominant in 1Mn alloy,the β1’ martensite is dominant in 2Mn alloy and 3Mn alloys,and the β1’martensite and a small amount of unconverted martensite β1 phase are dominant in 4Mn and 5Mn alloys.In addition,the grain refinement degree of 1Mn alloy to 3Mn alloy was very apparent in the as-deposited and quenched microstructures.However,with a further increase of Mn content,the grain size of 3Mn alloy to 5Mn alloy is almost the same.Analysis suggests that the changes in alloy microstructure are not only related to the increase in Mn content and the introduction of O when Mn content is very high but also to the special heat and mass transfer mechanism of additive manufacturing with powder core wire.(3)The properties of Cu-12.5A1-xMn(x=1,2,3,4,5)alloy produced by additive manufacturing technology with powder core wire were studied.The results showed that the shape recovery rate of all five alloys remained above 65%under 4%pre-strain,and the shape recovery rate showed a pattern of first increasing and then decreasing from 1Mn alloy to 5Mn alloy.Among them,3Mn alloy had the highest shape recovery rate(79.41%),while 5Mn alloy had the lowest shape recovery rate(65.63%);Meanwhile,the hardness of the deposited microstructure gradually decreases,while the hardness of the quenched microstructure first decreases and then increases.In addition,through tensile experiments,the tensile strength and elongation of 1Mn and 2Mn alloys are extremely low,the tensile strength of 3Mn to 5Mn alloys gradually increases,and the elongation gradually decreases due to the combined effects of grain refinement and Al2O3 particles.The analysis shows that the main factors affecting the shape recovery rate of the alloy are the transformation amount of martensite,the order degree of martensite,and the grain size,etc.The analysis shows that the main factors affecting the shape recovery rate of the alloy are the transformation amount of martensite,the order degree of martensite,and the grain size,etc.The main factors affecting the hardness of the alloy are γ2 precipitated phase,grain size,O element,etc.The tensile properties of alloys at room temperature are mainly influenced by precipitates,grain size,and degree of oxidation.(4)The regulatory effect of the fourth phase element Fe on the Cu-Al-Mn alloy produced by additive manufacturing technology with powder core wire was explored.Research has found that after adding lwt.%Fe,the transition from hypereutectoid to eutectoid composition in the production of Cu-Al-Mn alloy,thereby inhibiting brittleness γ2 phase precipitation.Meanwhile,the formation of a new phase κ phase makes the width and substructure of martensite finer after quenching,and at the same time,the alignment consistency within and between grains becomes better.At the same time,after adding lwt.%Fe,the shape memory properties of Cu-Al-Mn alloy significantly improved.The shape recovery rate was 100%when the pre-strain was 4%-8%,and it did not decrease until the pre-strain increased to 10%but remained above 90%.In particular,the 1Fe alloy exhibits an explosive recovery behavior,which begins to recover within less than 2s and returns to the state before deformation within 5s.In addition,after adding 1wt.%Fe,the quenched hardness and tensile strength increased,but the as-deposited hardness and elongation decreased.Analysis suggests that the regulatory effect of Fe on the Cu-12.5Al-3Mn alloy produced by additive manufacturing technology with powder core wire is mainly related to inhibition γ2 precipitation and the formation of new phases κ related to the impact it brings.