Study On Mechanics And Corrosion Resistance Of Al_XCoFeMn(Cu,Ni) High Entropy Alloys

High entropy alloys（HEAs）are considered to be a structural and functional material with promising applications,due to the unique microstructure and excellent properties they possess.The unique properties of different systems and compositions,along with the wide scope of compositional design,have made high entropy alloys enduringly hot in fields related to materials research.This paper discusses the preparation of low-density high entropy alloys with strength and ductility by adding Al elements to adjust the microstructure and reduce the density of the alloy from the alloy composition design and processing process and properties of the alloy,in order to respond to the new opportunities of high entropy alloys brought about by the increasing demand for more comprehensive alloy materials in industrial production.The novel Al_xCoFeMnNi HEAs in the as-cast state was prepared by vacuum arc melting as the object of study,and the annealed Al_xCoFeMnNi alloy and the as-cast Al_xCoFeMnCu alloy were obtained by annealing treatment at 1000℃/12 h and replacing the Ni element with Cu element,the microstructure,mechanical properties and corrosion resistance were systematically investigated.The influence of Al element and Cu instead of Ni on the structure and properties of CoFeMnNi high entropy alloy is discussed in depth,which provides a reference for the design of lightweight,high strength,excellent corrosion resistance high entropy alloy.The main conclusions of the research are as follows:（1）The increase of Al content causes the alloy appear in BCC phase at Al content x=0.5.The density of the alloy all decreases and the hardness increases with the increase of Al content,and the change of alloy hardness is mainly influenced by the microstructure of the alloy.（2）In the as-cast Al_xCoFeMnNi alloy,the gradual addition of Al elements caused the microstructure of the alloy to transition from a single-phase FCC to a dual-phase FCC+BCC structure and finally to a single-phase BCC structure.The increase of Al can increase the compressive yield strength of the alloy within a certain range,but the as-cast Al CoFeMnNi alloy was found to be severely brittle,with much lower compressive fracture strength and strain rate,and did not undergo the yielding process.The corrosion resistance of the alloy increases first and then decreases with increasing Al content.（3）The microstructure of the Al_xCoFeMnNi alloy underwent different changes after annealing at 1000℃/12 hours.The CoFeMnNi and Al_0.25CoFeMnNi alloys still have FCC single-phase structures,and no dendritic segregation phenomenon has been observed in the alloys.The other 3compositions of the alloys possess precipitated phases,presenting FCC+BCC dual-phase structure.The annealed Al_0.5CoFeMnNi alloy showed a large number of needle-like BCC phases in the FCC phase in the dendritic region,while the annealed Al_0.75CoFeMnNi and Al CoFeMnNi alloys were the ones with needle-like FCC phases in the BCC phase.The compression process of the alloys thus undergoes a large transformation,and the plasticity of the Al CoFeMnNi alloys is improved.However,there is a general decrease in the corrosion resistance of the alloy.（4）In cast Al_xCoFeMnCu alloys,alloys contain a Cu-rich FCC phase due to the segregation of Cu elements,and alloys with higher Al content have a certain ductility along with increased strength.The Al CoFeMnCu alloy has the highest hardness,compressive yield strength and corrosion potential among all alloys,while having a low density.