Study On Microstructure And Properties Of Al Matrix Composites Reinforced By High Entropy Alloy

Ceramic particle reinforced aluminum matrix composites have the characteristics of high specific strength,high specific stiffness,high wear resistance,high thermal conductivity,low thermal expansion coefficient,etc.,which can be widely used in aviation,aerospace,automobile,nuclear power and other fields.However,the poor plasticity and toughness of traditional ceramic granule reinforced aluminum matrix composites limit their application in structural materials.Therefore,how to make particle reinforced aluminum matrix composites with high strength,high hardness and good plasticity has always been the focus of research in this field.The high entropy alloy not only has better properties than the traditional alloy,such as high temperature creep resistance,high temperature oxidation resistance,corrosion resistance,high strength and high hardness,but also has excellent interface wettability,which can be used as a reinforcing phase to effectively improve the performance of the material.As a new additive manufacturing technology,row members prepared by selective laser melting not only have good surface precision and performance,but also have high material utilization.In this paper,aluminum alloy and high entropy particles were mixed evenly by vacuum ball milling,and then the composite materials were prepared by selective laser melting.By means of scanning electron microscope,electronic analysis balance,brinell hardness tester and universal testing machine,the effects of technological parameters on the microstructure and mechanical properties of composites were studied.The main conclusions are as follows:(1)after polishing and corrosion,the surface of high entropy alloy composites can be observed to be covered with a large number of strip and oval melting channels.Under the scanning electron microscope(sem),the composite material can be observed mainly in gray and black areas,with a few bright white areas.EDS detection showed that the gray area was high entropy alloy particles,and the contents of Fe,Co,Ni and Cr were significantly higher than other areas.The black area and the bright white area are the aluminum alloy matrix,rich in Al and Si elements,among which the bright white area can be speculated to be incomplete melting particles.When the laser power is too high,the distribution of high entropy alloy particles is concentrated and the surface contains pores.(2)the main defect forms of composite materials prepared by SLM are holes,cracks and partially melted metal particles.The insufficiently melted metal powder,metal oxide and metal carbide are mainly contained in the cavity.When the laser power,scanning speed and scanning spacing are 180 W,1000mm/s and 0.07 m respectively,the microstructure of the composite material is the most intact,with no obvious defects on the surface.The scanning speed has the greatest influence on the defects.If the scanning speed is too small or too high,a large number of holes and cracks will appear.It is easy to produce incomplete melted powder when the scanning spacing changes.(3)when the scanning speed is fixed,the density of composites increases first and then decreases with the increase of laser power.When the laser power reaches 180 W,the density of composites reaches the highest.When the laser power is fixed,with the increase of thescanning speed,the variation trend of the density of the composite material also increases first and then decreases.When the scanning speed reaches 1200,the density of the composite material reaches the highest.Among them,when the laser power is 180 W and the scanning speed is 1100mm/s,the density reaches the highest 99.6%.(4)the mechanical properties of high entropy alloy reinforced aluminum matrix composites by selective laser melting are higher than that of ceramic particle reinforced aluminum alloy and much higher than that of matrix aluminum alloy.Under the optimal conditions of process parameters,the hardness of the composite material is 138 HB,which is41.6% higher than that of the ceramic granule reinforced aluminum alloy and 63.8% higher than that of the matrix material.The higher the density of the composite material,the better the tensile performance and the highest yield strength of the composite material is 378 MPa,which is 38.6% and 38.4% higher than that of the aluminum alloy reinforced by ceramic particles.Its elastic modulus reached the highest 87.1GPa;The elongation at break reached12.1%.(5)the morphology of tensile fracture of composites with different densities is different.When the tensile fracture density is less than 97%,there are a small number of cleavage surfaces,dimples and unmelted powder particles in the tensile fracture,which has the characteristics of cleavage fracture of ductile and brittle mixture.When the tensile density reached 97%,the fracture surface was full of deep and large dimples,showing a typical ductile fracture,showing a good match between strength and toughness.With the increase of scanning speed,the tensile fracture contains alloy particles that have not completely melted.