Mechanical Properties Of 7075aluminium Matrix Composites Reinforced By Bimodal-sized Particles

Particle-reinforced aluminum matrix composites have excellent comprehensive properties,such as low density,high specific strength and specific modulus,which have been sucessfully used in aerospace,weapon equipment,transportation and electronic products.With the rapid development of modern science and technology,the mechanical properties of particle reinforced aluminum matrix composites have become more and more strict requirements.it is necessary to further improve their strength,while maintaining their considerable plasticity,to achieve a good match between high strength and high toughness.Hybrid reinforcement design is one of the strategies to obtain high strength and high toughness particle reinforced aluminum matrix composites.Hybrid enhancement can combine different reinforcing phases together,so that the reinforcing phases can play their respective strengthening roles and produce hybrid strengthening effect,so as to obtain excellent comprehensive performance.The development of hybrid reinforced aluminum matrix composites will pave the way for expanding the application range of particle reinforced aluminum matrix composites.At present,although the hybrid reinforced aluminum matrix composites have obtained better mechanical properties,the problem of mismatch between strength and toughness is still very prominent.How to obtain higher properties of aluminum matrix composites by hybrid strengthening of micro and nano particles is still worth further exploration.In addition,the strength and toughness mechanism and failure mechanism of the hybrid reinforced aluminum matrix composites with micro/nano particles also need to be further studied.In this paper,the bimodal-sized particles reinforced 7075 aluminum matrix composites were prepared by high-energy ball milling combined with vacuum hot pressing sintering process.The microstructure,quasi-static compression properties,dynamic compression properties,deformation and fracture failure modes of the composites were studied,and the hybrid strengthening effect of bimodal-sized particles was explored.The main work is as follows:1.The quasi-static compression performance of 7075 aluminum matrix composites reinforced by bimodal-sized particles were studied by changing the ratio of micro/nano reinforced particles and milling speed.The results show that the change of ball milling speed and particle ratio will affect the microstructure and mechanical properties of the composite.The composite prepared by the ball milling speed of 180 rpm and the particle ratio of 10 vol.%micron Al₂O₃and 5 vol.%nano Al₂O₃has excellent quasi static compression performance.2.The differences of surface morphology,quasi-static compression performance,deformation and fracture failure modes between bimodal-sized particles reinforced 7075aluminum matrix composites and single Al₂O₃particle reinforced 7075 aluminum matrix composites were compared and studied.The results show that,on the one hand,the addition of mixed particles can affect the distribution of elements in the alloy matrix and generate intermetallic compounds.On the other hand,it will affect the interface bonding between the micron Al₂O₃particles and the matrix,and change the crack propagation mode and material failure mode of the composite.The bimodal-sized particles reinforced 7075 aluminum matrix composite has the ultimate compressive strength of 1150 MPa and the failure strain of 8.92%,which is far better than the quasi-static compression performance of the single Al₂O₃particle reinforced 7075 aluminum matrix composite.3.The dynamic compression performance of 7075 aluminum matrix composites reinforced by bimodal-sized particles at different strain rates were investigated.The results show that the ultimate compressive strength and failure strain of the hybrid composite increase with the increase of strain rate.When the strain rate is 3000 s^-1,the ultimate compressive strength of the hybrid composite reaches 1181 MPa,and the failure strain reaches 9.85%.At high strain rate,aluminum alloy matrix melting occurs in the hybrid composite,which increases the failure strain of the hybrid composite.The results show that the bimodal-sized particles reinforced 7075 aluminum matrix composite has excellent dynamic compression performance and has a good application prospect in the field of armor.4.Based on the results of mechanical properties test and microstructure characterization,the strengthening mechanism of 7075 aluminum matrix composites reinforced by bimodal-sized particles was discussed.In hybrid composites,the following mechanisms contribute significantly to strengthening:(1)Load transfer strengthening of micron and nano Al₂O₃particles;(2)Fine grain strengthening caused by particles hindering grain growth during sintering;(3)Orowan strengthening induced by dispersion of nano-Al₂O₃particles in metal matrix;(4)Hybrid strengthening effect of micro and nano particles is embodied in changing the geometric necessary dislocation density around the micron Al₂O₃particles,improving the interfacial bonding ability between particles and matrix,and improving the matrix strength.