Research On Microstructure And Mechanical Properties Of Continuous Al₂O_3f/Al Composites Manufactured By Vacuum Pressure Infiltration

Owning to their combined advantages of high specific strength, high specific stiffness, excellent thermal stability, fatigue resistance, wear resistance and design flexibility, continuous Al₂O₃ fiber reinforced aluminum matrix composites have an urgent demanded in the field of modern aerospace and national defense technology. The preparation of continuous Al₂O_3f/Al composites by vacuum infiltration and infiltration can realize the integration of material preparation and forming, but in the process of preparation, the poor wettability of the fiber and the matrix caused complete infiltration is difficult to achieved as well as the fiber damage, the interface control and other issues.In this paper, the effects of different fiber preheating temperature and different matrix alloys on the microstructure, fiber damage and mechanical properties of continuous Al₂O_3f/Al composites were studied from the perspecitive of the preparation process and the change of the matrix alloy.In this paper, the Nextel 610 Al₂O₃ fiber is reinforcing material and the 1A99,ZL210 A, ZL301 and 7075 aluminum alloys are matrix alloys. The volume fraction of the Al₂O_3f/Al composites is 40%, and the composite was prepared by the vacuum pressure infiltration. The effects of fiber preheating temperature on the density and microstructure of continuous Al₂O₃f/ZL210 A composite were studied, and the densification mechanism was studied, and focus on research the effects of matrix alloy on the fiber damage, microstructure and mechanical properties of continuous Al₂O_3f/Al composites. The main conclusions are as follows.The influence of fiber preheating temperature on the density and microstructure of continuous Al₂O₃f/ZL210 A composites was obvious, the composite can not be completely impregnated with the preheating temperature at 500℃. Preheat temperature increased to 530℃, the density of the composite increased significantly to 98.8%, and the composite tissue defects were reduced, and the fiber segregation degree was lower.When the preheat temperature is increased to 560℃, the density of the composite is99%, the increase of the density and the improvement of the microstructure improvement was small.Matrix alloys have obvious influence on the density and microstructure of the composites, the densities of continuous Al₂O₃f/1A99, Al₂O₃f/ZL210 A, Al₂O₃f/ZL301 and Al₂O₃f/7075 composites were 96.8%, 98.8%, 99.2% and 98.1%, respectively. Due tothe poor wettability of the fiber/matrix, the continuous Al₂O₃f/1A99 composite have a large infiltration pore. There is more fiber segregation and infiltration micro holes in the continuous Al₂O₃f/ZL210 A composite, and the Al2 Cu in the matrix is gathered around the fiber. There is a small amount of fiber segregation and infiltration micro holes in the continuous Al₂O₃f/ZL301 composite, Mg in the matrix is evenly distributed. There are some infiltration pores and fiber segregation in continuous Al₂O₃f/7075 composite, the main alloying Zn distribute in the matrix is disarray. The main reason for this difference is the casting property of the matrix is different and the effect of different alloying elements on the wettability is different.The continuous Al₂O₃f/1A99 and Al₂O₃f/ZL210 A composites XRD and TEM analysis showed that the interface was smooth and clean, and the interfacial reaction was weak. The continuous Al₂O₃f/ZL301 composite had interfacial reaction generated MgAl2O4, the continuous Al₂O₃f/7075 composite had serious interfacial reaction generated Al2（SiO4）O and ZnAl2O4. The strength of Al₂O₃ fiber extracted from Al₂O₃f/1A99, Al₂O₃f/ZL210 A, Al₂O₃f/ZL301 and Al₂O₃f/7075 composites were 79.7%,75.7%, 72.3% and 44.7% of the fiber precursor, respectively. The surface of fiber is smooth and there is small amount of attachment which extracted from the continuous Al₂O₃f/1A99 and Al₂O₃f/ZL210 A composites. The surface of fiber is slightly rough and small amount of attachment which extracted from the continuous Al₂O₃f/ZL301 composite. The surface of fiber extracted from the continuous Al₂O₃f/7075 composite is very rough and there are many attachments. The degree of interface reaction between different matrix and fiber is different. Eventually, the damage degree of the fiber is different. The method of extracting the fiber from the composites is more simple and intuitive than the TEM method to judge the interface reaction of the composites.The strength of 1A99, ZL210 A, ZL301 and 7075 matrix alloys prepared under the conditions of preheating temperature 530℃, infiltration temperature 720℃, infiltration pressure 7MPa and holding time 5min were 66 MPa, 165 MPa, 126 MPa and 122 MPa respectively, the tensile strength of the corresponding four kinds of composites were465 MPa, 479 MPa, 680 MPa and 389 MPa, the tensile strength of the continuous Al₂O₃f/ZL301 composite reached 71.5% of the theoretical value. The strength of the base alloy is not the main factor affect the strength of the Al₂O_3f/Al composites. The interfacial reaction degree and the fiber damage are the main factors to determine the strength of the composite.The SEM analysis of the fracture of the composites showed that the fracture of the continuous Al₂O₃f/1A99 composite was uneven, and the fibers were pulled out for along period. The fracture was irregular of the continuous Al₂O₃f/ZL210 A composite material, only a small amount of fiber was pulled out, both of them are a typical weak interface. The fracture of continuous Al₂O₃f/ZL301 composite is uneven, more fiber was pulled out, the interfacial bonding strength is moderate. The fracture of the continuous Al₂O₃f/7075 composite material was flush, no fiber was pulled out, characterized by strong interface bonding. The micro defects and interface bonding strength of composites are the main factors affect the fracture mechanism.