Research On The Wear Mechanism Of CNTs/Al Composites By Rotational Friction Extrusion Process

The 5A06-H aluminum alloy matrix composites reinforced with the volume fraction of 1%~5% carbon nanotubes(CNTs) were fabricated by Rotational Friction Extrusion(RFE) processing. The effect of RFE processing and the volume fraction of CNTs on the forming, microstructure and hardness of the composite were investigated.The friction coefficient and wear rate of CNTs/5A06 Al composites were measured by wear test. The structural characteristics of wear surface, sub surface and wear debris were observed by SEM. Then the wear mechanism was analyzed at different stages of friction.The results show that the bulk composites with certain dimension can be fabricated by the RFE processing. The microstructure of the composites appear fine equiaxed grain and no defects exist in the composites. The CNTs are uniformly distributed in the composite, and the reaction between CNTs and matrix materials produced the Al4C3.The hardness of the composite increase first and then decrease with the increase of the content of CNTs. When the volume fraction of CNTs is about 4%, its hardness is about20% higher than that of the original Al matrix material by RFE process.RFE process can reduce the friction coefficient and wear rate of The aluminum matrix. With the increase of the content of CNTs, the friction coefficient and wear rate of the composites both increase firstly and then decrease. The friction coefficient and wear rate of 4% CNTs/5A06 Al composite are 0.218 and 0.1099×10-3mm3/J, they are reduced by 16.5% and 42% compared to the aluminum matrix by RFE processing.A smooth lubrication film is formed on the worn surface of CNTs/5A06 Al composites. The sub surface is a layer structure, which can be divided into three regions,the lubricating film, the plastic deformation layer and the undeformed composite. The wear mechanism of 5A06-H is mainly serious adhesive wear and slight abrasive wear.The wear mechanism of matrix material by RFE processing is adhesive wear and abrasive wear. The wear mechanism of 3% CNTs/5A06 Al composite is delamination wear and abrasive wear.The process of sliding friction of CNTs/5A06 Al composites can be divided into running in stage, unstable friction stage and stable friction stage. In the running in stage,the wear is mainly the shear and failure of the contact point between the composites andthe friction pairs. The wear mechanism of the unstable friction stage is mainly adhesive wear and abrasive wear. The wear mechanism of the stable friction stage is mainly delamination wear which the lubrication film was peeled off and abrasive wear. There are two mechanisms of the crack in the delamination wear, one is the crack from the surface and the other is the crack from the near surface.