Fabrication And Properties Of 6061Al Matrix Composites Reinforced By AlSiTi High Entropy Alloy

Ceramics particulate reinforced aluminum matrix composites possess high specific strength,high hardness and good wear resistance,while these composites have poor ductility and toughness because of poor wettability between ceramics and metal matrix.These defects give rise to the great limitation for their application in structure materials.How to improve the hardness and strength of composites as well as keep good ductility,is the researchers pursuing goal.High entropy alloys(HEA),a new type of materials,have exceptional mechanical and physical properties.Owing to metal-metal natural interface bounding feature,it has proved that HEAs particles show good interfacial wettability and physicochemical compatibility with Al,Cu alloys,thus HEAs can significantly improve the mechanical properties of matrix.Consequently,HEAs particles would be suitable candidates of reinforcements for aluminum matrix composites.At present,there are a few literatures have been reported on aluminum matrix composites reinforced by HEAs,especially low-density HEAs.In this work,low-density HEAs are fabricated by mechanical alloying and spark plasma sintering,the microstructure and mechanical properties of bulk HEAs are studied.Low-density AlSiTi HEAs are selected as reinforcements and 6061 Al is selected as matrix.(AlSiTiCrNiCu)p/6061 Al composites are synthesized by spark plasma sintering.The effects of HEAs particles contents and sintering temperature on the interface characteristic,mechanical properties and thermal properties are researched.The following results are mainly obtained:(1)The lightweight AlSiTiCrNiCu HEAs with BCC structure are well prepared by mechanical alloying and have excellent homogeneity in composition.The microstructures of bulk HEAs consist of light-colored areas and dark areas.AlSiTiCrNiCu alloys shows high strength and hardness,but poor ductility.The alloys,sintered at 1000 °C,have excellent comprehensive mechanical properties at room temperature,with the hardness,compression strength and strain of 923 HV,2462 MPa and 3.7 %,respectively.Fracture characteristic of the alloys is intergranular fracture.(2)The AlSiTiCrNiCu HEAs particles distribute on 6061 Al matrix uniformly and the composite powders are consolidated into highly dense(98 %)bulk specimens by SPS.There are two types of interfaces on(AlSiTiCrNiCu)p/6061 Al composites,which are mechanical interface and diffusional interface,respectively.The sintering temperature has a great effect on boundaries between matrix and reinforcement.The interfaces are mainly mechanical interface at low sintering temperature.As the sintering temperature increasing,the boundaries mainly are diffusional interface.(3)The composites have a significant hardness and strength enhancement when adding HEAs and the effects of reinforcement on ductility are smaller than ceramics particulate.When the volume fraction of HEAs is 10 %,the(AlSiTiCrNiCu)p/6061 Al composites show the hardness of 110 HB,the yield strength of 218 MPa,the compression strength of 659 MPa and compression strain of 35.6 %.The higher reinforcement particles contents,the higher hardness and strength of composites,and the composites keep good plasticity.With increasing of sintering temperature,the hardness and yield strength of(Al Si TiCrNiCu)p/6061 Al composites are enhanced,while the compression strength and compression ratio first increase and then become lower.The composites sintered at 520 °C have excellent comprehensive mechanical properties.(4)The coefficient of thermal expansion(CTE)of composites decrease when adding HEAs particles.The mean coefficient of thermal expansion(25 °C~100 °C)of composites are found in the range of 19.1~22.2 ×10-6/°C.With increasing of HEA particles,the coefficient of thermal expansion of(AlSiTiCrNiCu)p/6061 Al composites decrease.The thermal conductivity of composites are found in the range of 60.1~112.6 W/(m·K).The higher reinforcement particles contents,the lower thermal conductivity(TC)of composites.