| Aluminum and its alloys have replaced steel in some industrial fields due to its low density,high thermal conductivity,good mechanical properties,and corrosion resistance.However,the low wear resistance limits further applications as a wear-resistant material.Therefore,it is necessary to improve the wear resistance of aluminum alloys.In this paper,the 2024 aluminum alloy was used as the base metal(BM),adding carbon nanotubes(CNTs)into BM by drilling,powder filling method,fabricating CNTs/2024 Al composites with CNTs volume fraction of 1% to 5% by rotating frictional extrusion(RFE)processing.Wear test of the composites before and after heat treatment was done under different frictional conditions with a disc-type wear equipment.The effects of CNTs volume fraction,heat treatment state,frictional load and speed on the wear properties and characteristics of the composites were investigated.Conclusions could be drawn as followed:CNTs/2024 Al composites with good appearance and uniform distribution of microstructure and hardness were successfully fabricated by RFE processing.After RFE processing with no addition of CNTs,precipitate coarsening and reduction in quantity were found in the aluminum matrix.In addition,the precipitate/α-Al interface changed from coherent to semi-coherent,softening aluminum matrix.Increasing CNTs content in Al matrix,the number of precipitates and the hardness value gradually increased in comparison with BM.After heat treatment,the amount of precipitates increased with the precipitate/α-Al interface changed from semi-coherent to coherent,which let the composites were harder than BM.With the increase of CNTs content,the wear coefficient and rate of the composites decreased and then increased.When the CNTs content is 4%,both the wear coefficient and rate reached the minimum,which are 8% and 49.1% lower than the BM,respectively.The wear-coefficient fluctuation of the heat-treated composites in the friction process was similar to those before the heat treatment.But the wear coefficient and rate were lower than those before the heat treatment.With the increase of the frictional load,the wear coefficient and rate of the composites gradually increased.When the load was 40 N,the wear coefficient and rate of composites are the lowest,which were 9.7% and 46.1% lower than the BM,respectively.And the wear coefficient and rate of composites gradually decreased with the increase of testing speed.When the frictional speed reached to 400 rpm,the wear coefficient and rate were minimum,which were 11.4% and 65.2% lower than the BM,respectively.Wear characteristics of composites changed with increasing CNTs: When CNTs content was 2%,the composite wear surface formed a complete interfacial film with the wear characteristic is slight adhesive wear.When CNTs content was 5%,many pits and furrows were found at the surface of the composite after wear testing,and the degree of adhesive wear increased with slight abrasive wear.After heat treatment,due to the hardness augment of the composites,the surface enhanced the resistance of plowing.When the CNTs content was 2%,the wear characteristic is similar to that before the heat treatment.When the CNTs content was 5%,the degree of abrasive wear decreased.When the frictional load was small,the interfacial film of the composite is smooth and the surface furrows are of great number with abrasive wear.When the frictional load was large,the interfacial film fell off from the wear surface severely with adhesive wear.When the frictional speed was slow,the composites wore many large and deep surface pits.The interfacial film was incomplete with the adhesive wear.When the friction speed was fast,the surface of the composite material wore more furrows with abrasive wear. |
