| Compared with micron particles,nano-SiC particles have higher reinforced efficiency and broad application prospects in the preparation of aluminum matrix composites with high strength and excellent machining performance.As a new type of flexible nanomaterials,carbon nanotubes(CNTs)own high theoretical strengthening efficiency and potential in the preparation of high-strength aluminum matrix composites.However,the single CNT reinforcement Aluminum matrix composite has the disadvantages of insufficient material modulus and hardness.Theoretically,the hybrid effect makes the composite properties of hybrid reinforced aluminum matrix composites better than that of single reinforced aluminum matrix composites.Therefore,we investigated the mechanical properties and friction and wear behaviors of CNT and micron SiC particles hybrid reinforced aluminum matrix composites.In the first part,nanometer SiC/7055 Al and CNT/7055 Al composites were prepared by high energy ball milling,powder metallurgy and hot extrusion with 7055 Al as the matrix,and the relationship between their microstructure and mechanical properties was studied.In the second part,the composites of micron SiC/7055 Al and micron SiC-CNT /7055 Al were prepared using 7055 Al as the matrix by high energy ball milling,powder metallurgy and hot extrusion process.The microstructure and mechanical properties of the two composites were characterized.In the third part,the dry sliding friction and wear properties of three kinds of composites,namely micron SiC/7055 Al,CNT/7055 Al and micron SiC-CNT/7055 Al,were tested with the pin to pan friction and wear tester.The wear mechanism was compared and analyzed,and the following conclusions were obtained:1.Dense nano-SiC/7055 Al and CNT/7055 Al composites were prepared by high energy ball mill,powder metallurgy and hot extrusion process.In the two composites,nano-SiC particles and CNT were randomly distributed in the matrix alloy without obvious interface reaction.Due to the addition of nano-SiC or CNT reinforcement,the yield and tensile strength of the composites were improved to certain extent.The yield strength and tensile strength of matrix was increased by 52 MPa and 53 MPa for every addition of 1.0 vol.%CNT,while it was 37 MPa and 20 MPa for every addition of 1.0vol.%SiC.Therefore,CNT is better than nano-SiC in strengthening efficiency.2.The compact of micron SiC/7055 Al and micron SiC-CNT/7055 Al composites were prepared by high energy ball milling,powder metallurgy and subsequent hot extrusion process.The CNT and micron SiC in the composites were dispersed evenly without agglomeration.Interface observation showed that there was precipitation free zone near the micron SiC in SiC/7055 Al composite,resulting in its strength even lower than that of the 7055 Al matrix alloy.The tensile strength of hybrid reinforced composites is higher than that of two single reinforced aluminum matrix composites and alloy matrix.Compared with the matrix,the yield strength and tensile strength of the hybrid composite increased by 64 MPa and 61 MPa,respectively.3.The dry friction and wear experiment results shows that the wear rate of both single and hybrid reinforced composites increases with the increase of load.At low load(0.5 MPa),the wear rate of micron SiC-CNT/7055 Al composites was lower than that of single reinforced CNT/7055 Al and single reinforced micron SiC/7055 Al composites.Increaseing the load to 2.0 MPa,the wear rate of hybrid reinforced composites was higher than that of the single CNT or micron SiC/7055 Al composites.The wear surface morphology analysis shows that composite wear mechanism is divided into the following three conditions: the first stage belongs to the mild wear stage,mainly of abrasive wear,there also existed some adhesive wear.The second stage belongs to the mechanical mixing layer formation stage,mainly adhesion wear.The third stage is mechanical mixing layer stripping stage,after the formation of adhesive wear at this time. |
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