Microstructure And Mechanical Properties Of SiCp/2024 Composites

SiCp/Al composites has the characteristics of high specific strength and specific rigidity,good thermal conductivity and wear resistance.It has a broad application prospect in aerospace,automobile,military industry and other fields.The SiCp/Al composites prepared by conventional powder metallurgy process has the advantages of uniform distribution of SiC particles and no interface reaction,and avoiding the low wettability of SiC particles and aluminum alloy.However,the influence of SiC particles and aluminum alloy matrix microstructure on the mechanical properties of the composites is not clear,and the mechanical properties of the composites need to be further improved.In this paper,SiCp/2024 composites was prepared by powder metallurgy method.The densification,microstructure,interface and mechanical properties of SiCp/2024composites were studied.The influence of SiC content(37vol.%and 55 vol.%)on the mechanical properties of SiCp/2024 composites was analyzed.The effects of changing hot press temperature and secondary hot pressing methods on the microstructure and mechanical properties of SiCp/2024 composites and related mechanism were explored.The main results are as follows:(1)The composites of 37 vol.%and 55 vol.%SiCp/2024 were prepared by powder metallurgy method.SiC particles are evenly distributed in the aluminum alloy matrix.With the increase of SiC content from 37 vol.%to 55 vol.%,the relative density of hot pressed SiCp/2024 composites decreased from 99.3%to 99%;37 vol.%There are a few small holes in the aluminum alloy matrix of SiCp/2024 composites,accompanied by a small amount of SiC particles fracture and fragmentation,and a small amount of SiC particles agglomeration in local areas;the hole size of 55 vol.%SiCp/2024 composites is large,the phenomenon of SiC particles cracking and fragmentation increases significantly,and the phenomenon of SiC particles agglomeration in local areas increases.(2)SiCp/2024 composites were prepared by powder metallurgy.The liquid phase was mainly distributed at the interface between aluminum alloy and SiC particles during hot pressing.The precipitates in hot pressed SiCp/2024 composites are disc-like or sheet-like Al₄Cu₉ phase and thick strip-like or dendritic S(Al₂Cu Mg)phase.After T6 heat treatment,the disc-like or sheet-like Al₄Cu₉ phase in the composites changes into?(Al₂Cu)phase and thick and eccentric strip-like The S(Al₂CuMg)phase still exists.(3)With the increase of SiC content from 37 vol.%to 55 vol.%,the average modulus of elasticity of SiCp/2024 composites increases from 161 GPa to 205 GPa,and the average strength decreases from 397.8 MPa to 328 MPa;the fracture of 37vol.% SiCp/2024 composites is mainly ductile fracture of aluminum alloy,and the crack propagates along the interface with brittle fracture of SiC particles;55 vol.%The fracture of SiCp/2024 composites is mainly brittle fracture of SiC particles,and a small amount of aluminum alloy ductile fracture.(4)SiCp/2024 composites were prepared by different hot pressing temperatures.The microstructure and mechanical properties of SiCp/2024 composites were affected by hot pressing temperature through influencing liquid phase network and densification.Appropriate hot pressing temperature is the key to improve the mechanical properties of SiCp/2024 composites.When the hot pressing temperature is535?,the composites have moderate liquid phase(4.65vol.%)and relative density(99.38%).The mechanical properties of the composites with 37 vol.%SiCp/2024 in T6 state reach a high level,and the tensile strength and elongation are 506 MPa and0.315%,respectively.(5)SiCp/2024 composites was prepared by secondary hot pressing method.The second hot pressing improves the relative density of the composites.The precipitated phases Al₂Cu and Al₂Cu Mg were smaller and distributed uniformly by secondary hot pressing.The mechanical property of T6 heat treatment state 37 vol.%SiCp/2024composites is greatly improved by the second hot pressing and reachs the highest level,its tensile strength and elongation are 540 MPa and 0.485%,which are 119 MPa and 0.276% higher than that of one-time hot pressing process respectively.