Mechanical Properties Of Nanoparticles/Twins Reinforced Aluminum Matrix Composites

As a kind of lightweight and high-performance structural material,particle reinforced aluminum composite has been widely used in aerospace and transportation fields due to its low manufacturing cost,lightweight,high modulus,high strength and good wear resistance.However,the difficulty of incompatibility between strength and plasticity limits the wider application of particle reinforced aluminum composites.Increasing the volume fraction of nanoparticles or adjusting the preparation process to introduce twins into the aluminum matrix may be an effective method to solve the problem of incompatibility between strength and plasticity of aluminum matrix composites.However,high volume fraction of nano particles is easy to agglomerate and the high stacking fault energy of aluminum matrix is not conducive to the formation of twins,which makes it difficult to prepare the related composites.Therefore,it is valuable to study the preparation,mechanical properties and deformation mechanism of aluminum matrix composites with high volume fraction and uniform distribution of nano particles or aluminum matrix composites with macro twins.In this paper,high volume fraction nano Al₂O₃/Al composites and Al₂O₃/Al composites with macro twins were prepared by high energy ball milling combined with vacuum hot pressing.The microstructure,mechanical properties and deformation mechanism of the composites were studied.The main research work is as follows:1.The microstructure of Al matrix composites reinforced with high volume fraction nano-Al₂O₃ particles was studied.The results show that the distribution of nano-Al₂O₃particles is uniform and the particle spacing is nanometer;With the increase of the volume fraction of Al₂O₃particles,the grain size of the composites decreases first and then increases,and the dislocation density increases first and then decreases.2.The mechanical properties of aluminum matrix composites reinforced with high volume fraction nano-Al₂O₃particles were studied.The results show that with the increase of the volume fraction of nano-Al₂O₃ particles,the compressive strength of the composite increases obviously,and the maximum compressive strength of 15vol.%-Al₂O₃/Al composite is 741 MPa,with 23%failure strain;,the failure mode changes from brittle-ductile mixed fracture to brittle fracture.3.The deformation mechanism of high volume fraction nano-Al₂O₃ particles reinforced aluminum matrix composites was studied.The results show that fine grain strengthening,load transfer strengthening,thermal mismatch strengthening and Orowan strengthening can significantly improve the compressive strength of the composites.When the volume fraction of nano-Al₂O₃particles reaches 15vol.%,the actual dislocation density in the composites is much lower than the theoretical value due to thermal mismatch strengthening;The deformation process of the composites is dominated by the interaction between nano-Al₂O₃particles and dislocations,which accumulate around the particles.4.The synergistic effect of nano-Al₂O₃ particles and twins on the microstructure of Al₂O₃/Al composites was studied.The results show that with the increase of preparation temperature,the content of Al₂O₃ particles in the composites increases;When the preparation temperature reaches 610?,macroscopic twins begin to form in the composites,with the further increase of the preparation temperature,the content of twins increases.5.The synergistic effect of nano-Al₂O₃ particles and twins on the mechanical properties and strengthening mechanism of Al₂O₃/Al composites was studied.The results show that the existence of twins can greatly improve the compressive strength and maintain good plasticity of the composites,and the strength of the composite increases significantly with the increase of twins content;The pinning effect of nano-Al₂O₃ particles to dislocation and the blocking of twins to dislocation movement are the main reasons for the strength improvement of the composites.