| Aluminum-matrix composites(AMCs)have excellent comprehensive properties and therefore have a wide range of applications in aerospace,military industry and medical devices.In this thesis,AMCs were prepared by powder metallurgy using 7075 aluminum alloy spherical particles as the matrix material and silicon carbide nanowhiskers(SiCw)as the reinforcement material.The preparation process,microstructure and properties of SiCw/7075 Al composites were studied extensively to provide scientific basis and technical guidance for the composition design and preparation of AMCs.And the following results were obtained.(1)The effects of ball milling process parameters on 7075 aluminum powder particles and SiCw/7075 Al composite powder particles were investigated.A more ideal ball milling powder can be obtained when the process parameters of ball material ratio of 3:1 and ball milling time of 0.5 h are selected.It was found that as the ball material ratio increased and the ball milling time increased,serious agglomerates would be formed between the powder particles,which would affect the uniform adhesion of the subsequent reinforcing particles on the metal powder.(2)The solidification forming process of 7075 aluminum alloy powder was studied.In the pressureless sintering forming process,the sintering temperature has a significant effect on the organization and properties of the aluminum alloy material.The low sintering temperature is not conducive to the bonding between the powders,and the high sintering temperature will lead to over-burning of the metal.The Vickers hardness of the aluminum alloy material tends to increase with the increase of the sintering temperature within a certain temperature range,and the best performance of the aluminum alloy material is obtained when sintered at 617 °C.In the hot pressing sintering process,the hot pressing pressure and the hot pressing temperature can have a direct influence on the properties of the aluminum alloy material.(3)The rolling heat deformation process can make the properties of the solidified formed aluminum alloy material further improved on the basis of the original mechanical properties.The hardness of the alloy material was improved by about88.76% when the pressureless sintering formed 7075 aluminum alloy was 20% under the rolling down pressure,while the cracking phenomenon appeared when the rolling deformation degree was further increased.For the hot pressing 7075 aluminum alloy material,with the increase of rolling deformation,the grain size is obviously reduced,and the dislocation density is improved while the grain size is reduced,and the hardness of the material becomes larger.The hardness of the alloy material increased by about131.1% when the rolling deformation is 50%.(4)The organization and properties of SiCw/7075 Al composites prepared by pressureless sintering + hot pressing sintering were investigated.It was found that the SiCw/7075 Al composites after pressureless sintering had various defects inside their tissues and were not conducive to the overall performance of the composites.When the SiCw content was 0.4 wt.%,0.8 wt.% and 1.6 wt.%,the tensile strength of the composites reached 443.2 MPa,471.0 MPa and 394.2 MPa,respectively,and the elongation reached 10.1%,8.9% and 7.3%,respectively,but the overall mechanical properties did not reach the ideal conditions.(5)The effects of different SiCw contents on the organization and properties of SiCw/7075 Al composites prepared by hot-press sintering were investigated.The results showed that with the increase of SiCw content,the grain size of the composites gradually decreased and The agglomeration behavior of SiCw in 7075 Al alloy was not conducive to the further improvement of the comprehensive properties of AMCs when the whisker reinforcement content reached 2.0 wt.%.When the SiCw content is 1.6wt.%,the best overall performance was achieved,with the tensile strength and elongation reaching 596 MPa and 8.6%,respectively. |
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