Preparation And Properties Of Aluminum-based Composites Reinforced With Amorphous Alloy And High Entropy Powder Particles

With the rapid development of industrialization and the further improvement of modern scientific and technological level,the exploitation of a new type of lightweight and high-strength composite materials has become the goal and pursuit in this field.Al-based composites have the advantages of low density,high elasticity modulus,high strength,good fatigue resistance,good abrasion resistance,good corrrosion resistance and low cost.It has become a star in the application field of metal matrix composites that are widely used in aerospace,national defense and automotive fields as the advanced engineering materials.In the present work,we designed and fabricated a novel Al-based composites reinforced with amorphous alloy or high entropy alloy（HEA）particles using mechanical alloying（MA）and spark plasma sintering（SPS）technique.The phase composition,reinforcement distribution and interfacial combination configuration were studied.The density,microhardness,mechanical properties and corrosion resistance of the bulk composites also were tested in detailed.The corresponding strengthening mechanisms were further discussed.The main conclusions are summarized as follows.1.Al₈₅Fe₁₅ amorphous alloy powders were prepared by MA,and the onset crystallization temperature reaches 1209 K.The Al₈₅Fe₁₅ amorphous alloy reinforced6061Al-based composites exhibit the good mechanical performance by SPS technique.The reinforcements possessing the amorphous characteristic distribute uniformly in the 6061Al matrix.The relative density of all composites is higher than 98%.Moreover,their microhardness values are all greater than 200 HV,which is better than that of 6061Al matrix（61 HV）.The composite containing 30 vol.%Al₈₅Fe₁₅ has the high yield strength of（478 MPa）,which is 273%higher than that of the matrix.The improvements of hardness and strength of composites are mainly due to the facts that the reinforcements remain amorphous and distribute evenly in the matrix.Besides,the composites have the better corrosion resistance in seawater solution.2.Al₈₅Fe₁₅ amorphous alloy/0.3wt.%graphene reinforced Al matrix composites were prepared by SPS.The Al₈₅Fe₁₅ reinforcements still remain amorphous characteristic after SPS process.When the additional amount is 10 vol.%,the reinforcement with the granular form is distributed evenly in the Al matrix.With increasing the addition amount up to 30 vol.%,the reinforcement presents the continuous network state.Compared with SPS-ed pure Al,30 vol.%Al₈₅Fe₁₅amorphous alloy/0.3 wt.%graphene reinforced Al matrix composite has the higher microhardness（83 HV）and yield strength（262 MPa）.According to the dynamic potential polarization curve,only 0.3 wt.%graphene reinforced composite in seawater solution has a wide passive region（0.44 V）,showing a good pitting resistance.3.CuZrAl glass reinforcements were prepared by MA,and Al-based composites with the better mechanical and corrosion properties were prepared by SPS.The composites have high microhardness and compressive fracture strength,while holding a certain amount of plasticity.During the sintering process,the CuZrAl amorphous phase crystallized.Besides the fcc-Al phase,the sintered products also include Al₃Zr and CuAl₂ phases.Both Al and Cu atoms all diffuse at the interface between matrix and reinforcement,promoting the formation of good interface.The microhardness of the composite with 20 vol.%reinforcemen is 290 HV,the yield strength is 408 MPa,and the fracture strength is 459 MPa,which is higher than the other composite materials.The second phase strengthening,continuous distribution of the reinforcement,the higher relative density,good interface bonding and fine grain strengthening are all helpful to the strength and hardness of the composite.In addition,the composite has a wide passive region in the seawater solution,and pitting resistance is improved,which is related to the Zr element easy formation of ZrO₂ or Zr（OH）₄ passivation film.4.CuZrAlTiNiW HEA reinforcements with body centered cubic（bcc）structure were prepared by MA,and the HEA reinforced Al matrix composites were fabricated by SPS.In addition to fcc-Al and bcc phase,a large amount of WAl₁₂2 phase and a small amount of Al₅Ti₃ and Al₅Zr₃ phases were generated.The composite containing30 vol.%reinforcement has the higher hardness value of 661 HV,and is 20 times higher than pure Al（32 HV）.The composite containing 20 vol.%reinforcement has high fracture strength（544 MPa）.The reinforcement exhibits core-shell structure in the matrix.The bcc solid solution is considered as the core,and the intermetallic compound precipitates around the core during the sintering process act as the shell（transition layer）.It leads to the better interface bonding between the matrix and reinforcement,which further improves the mechanical properties of the composite.In addition,the composites have the wide passive region and good pitting resistance in seawater solution.5.The CuZrAlTiNiW_0.2 HEA ribbons containing bcc solid solution and a small amount of unknown phases were prepared by the melt spinning process.By ball milling,the ribbons were smashed into powders with the size about 4μm,and the Al based composite with 10 vol.%reinforcement was prepared by SPS.The sintered products are fcc-Al,Ni₄Ti₃,AlCu₄ phase,and bcc phase disappears.The reinforcement also possesses the core-shell structure,and the shell area is rich in Al.The composites have the higher fracture strength（501 MPa）,and a good pitting resistance.6.In the present study,compared Al matrix,the Al-based composites all present the higher relative density,hardness,compressive fracture strength and good pitting resistance.30 vol.%CuZrAlTiNiW HEA reinforced Al matrix composites have the highest hardness value of 661 HV.The Al matrix composite（20 vol.%CuZrAlTiNiW）has the highest fracture strength（544 MPa）.However,CuZrAlTiNiW reinforced Al-based composites have no obvious plasticity.The fracture strength of the 20 vol.%CuZrAl reinforced Al-based composites is 459 MPa,the hardness is 290 HV,and the elongation is 18%.Through comparative analysis,CuZrAl reinforced composite presents the good comprehensive mechanical properties with high strengh and a certain amount of plasticity.Moreover,20 vol.%Al₈₅Fe₁₅ amorphous alloy reinforced6061Al matrix composite has the most extensive passivation platform（1.24 V）,presenting a good pitting resistance.