| Particle reinforced Al matrix composite materials are a kind of advanced structural materials with low density and high specific strength,it is widely used for high performance applications such as aerospace,electronics,automotive,military and other industries.The preparation methods of particle reinforced aluminum matrix composites are stirring casting,powder metallurgy,in-situ reaction,spray deposition and squeeze casting method.The paper developed the spraying-stirring equipment on the basis of the principle of stirring casting,and fabricated the high quality particle reinforced aluminum matrix composite.Using 7075 aluminum alloy as the matrix and Al2O3 particles as the reinforcement,with the numerical simulation technology,the experiment analyzed the particle movement and distribution,verified the microstructure change rule of the Al2O3p/Al(7075)composites,and then got the optimum fabrication parameters of composite material.Under the optimum parameters,the microstructure and mechanical properties of Al2O3p/Al(7075)composites were studied in different Al2O3 particles content and form,and the reinforcement mechanism of composites was explored.The main contents and results are as follows:The spraying-stirring method as a new technology was put forward for the first time to fabricate the composites.The main idea is to inject the enhanced Al2O3 particles into the inner part of the aluminum melt continuously with the stirring process at the same time,so that the particles could be evenly distributed in the melt.Based on this purpose the spraying-stirring equipment was manufactured and applied for the invention patent.It consists of heating system,stirring system,blowing system and mixing chamber,the composites can be fabricated in a short time when using the equipment.The equipment,which has simple structure,is easy to use and clean.The melt temperature,spraying-stirring time,injection types and quantity of the Al2O3 particles can be controlled accurately during the preparation of composite materials.In addition,both the enhanced Al2O3 particles and the 7075 alloy matrix are in the state of argon protection,further reducing the oxidation and ensuring the quality of the composite melt.The optimum fabrication parameters of Al2O3p/Al(7075)composite material was explored through numerical simulation and experimental analysis in the spraying-stirring process.The form of the stirring blade was designed and its location in the melt was determined.Also,the melt temperature,stirring speed and stirring time in the spraying-stirring process were studied.Research showed the optimum fabrication parameters of Al2O3p/Al(7075)composite material was that the melt temperature 700℃,the stirring speed 300r/min,the mixing time 15 min,the mixing blade in the form of three oblique leaf blade,and 20 mm from the bottom of the crucible.In this parameter,the distribution of particles in the melt is the most dispersed,and the grain size of the composite material is smaller,and the pores and defects are less.The Al2O3p/Al(7075)composite materials with different content of nano(0.5wt.%,1.0wt.%,1.5wt.%和 2.Owt.%)and submicron(2wt.%,4wt.%,6wt.%和 8wt.%)Al2O3 particles were prepared by the spraying-stirring method.The result showed that when the content of nano and submicronAl2O3 was 1.5wt.%and 4wt.%,The microstructure of the Al2O3p/Al(7075)composite materials was best.This is because both nano and submicron Al2O3 particles can play the role of heterogeneous nucleation and preventing grain growth in the solidification process of composites,but there is a limit of its content in the of spraying-stirring process.When the particles exceed a certain amount,the enhanced effect failure.Particles appear in the microstructure as impurities.After the mechanical property test,the tensile strength of composite materials was increased by 29%and 20%,and the hardness increased by 47%and 48%respectively.The Al2O3p/Al(7075)composite materials with double size nano/submicron mixed Al2O3 particles were prepared by the spraying-stirring method.The effects of a single size micron,nano and double size nano/submicron Al2O3p on the structure and mechanical properties of Al2O3p/Al(7075)composites were studied.The reinforcement mechanism of double size Al2O3p reinforced Al2O3p/Al(7075)composites was revealed.Result showed that the strengthening mechanism of micron particles is mainly fine grain strengthening and load transfer.In addition to the two reinforcement mechanisms mentioned above,there is an Orowan strengthening mechanism.The reinforcement mechanism of double size nano/submicron Al2O3 particles reinforced Al2O3p/Al(7075)composite material is Orowan reinforcement,fine grain strengthening and load transfer enhancement,Orowan reinforcement as the leading role.Test showed that the friction and wear modes of 7075 matrix alloy and Al2O3p/Al(7075)are mainly adhesive wear,abrasive wear and mild oxidation wear.The transfer film was formed on the surface of Al2O3p/Al(7075)composite evenly and firmly in the process of wear.The appearance of the transfer film makes the composites have more stable friction factor and reduces the direct contact wear of the material.In the wear process,the removal of the transfer film and the expansion of the subsurface cracks resulted in the flaking of the abrasive particles.Due to the appearance of the transfer film,the cutting function of the reinforcement in the composite material is weakened,and the wear surface of the material is not serious. |
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