Study On Microstructure And Properties Of Nano-Al₂O_3P/6061 Aluminum Matrix Composites

Aluminum matrix composites have the advantages of low density,high specific strength,high wear resistance,and its preparation method is simple and economical,which makes it widely used in aerospace,electronic devices and other precision structural parts.Nanoscale enhancement phase is added to the aluminum substrate preparation of aluminum matrix composites than the traditional composite materials in specific strength,corrosion resistance and thermal conductivity has more performance improvements,at the same time is also very good to improve the material under the high temperature strength and plasticity contradictory problem,but due to the inherent physical properties,nanoparticles on the preparation process is more difficult.This paper adopt the way of mechanical ball mill with vacuum hot-pressing sintering preparation 5%Al₂O_3p/6061aluminum matrix composites,the better solve the nano particles together,and matrix interface combined with the problems such as weak,samples of aluminum matrix composites is studied systematically in the mechanical ball milling,sintering temperature and solid solution aging microstructure and mechanical properties after heat treatment.The main research results are as follows;（1）The particle size and morphology of 5%Al₂O₃/6061 composite powder under different milling time were studied.The results showed that when the milling time was10h,the composite powder still became large particles.With the extension of the milling time,the powder surface was slightly cold welded,and appeared fine flakes after 40 h.It was found that the size of the composite powder decreased with the extension of ball milling time.After 50 h of ball milling,the balance between cold welding and crushing was reached,and the size gradually stabilized.（2）5%Al₂O_3p/6061 aluminum matrix composites were prepared by hot pressing sintering with rapid cooling after the melting point of aluminum alloy.The results show that with the extension of ball milling time,the density of the composites increases gradually,the hardness increases from 80.31 HV to 166.81 HV,and the tensile strength increases gradually with the extension of ball milling time.The maximum value is reached when the ball grinding time is 50 h,the tensile strength is 583 MPa,the elongation is 8.8%,showing good plasticity.The fracture morphology analysis shows that the sample under the ball grinding time belongs to the ductile fracture.TEM shows that the distribution of Al₂O₃ becomes more uniform with the extension of ball milling time,and the grain size of aluminum decreases gradually with a large number of dislocations.（3）The effect of sintering process on the microstructure and properties of the composites was studied.The results showed that the hardness and density of the samples increased first and then decreased with the increase of sintering temperature,and the tensile strength also showed the same law.At lower sintering temperature,there are a lot of pores in the tissue,resulting in lower density.When the sintering temperature is 580℃,the sample has the best performance,the density is 99.82%,the hardness is 211.97 HV,the tensile strength is 465 MPa,compared with low temperature sintering,the tensile strength is increased by two times.（4）In order to further improve the properties of 5%Al₂O_3p/6061 aluminum matrix composites,hot extrusion treatment was carried out to explore the effect of solution aging treatment on the microstructure and mechanical properties of the samples;The results show that under the same solution time,the hardness of the sample increases first and then decreases with the increase of solution temperature.Through the observation of microstructure,it is found that under the appropriate solution temperature,the faster the solution rate of the sample is,the more Mg₂Si phase is precipitated at the later stage,and the better the precipitation strengthening is.By comparing the microstructure of samples with different aging time,it can be found that short aging time cannot completely precipitate the second phase,while long aging time will lead to different degrees of coarse grain.In this experiment,when the aging mechanism is 170℃×12 h,the hardness of the sample is 160.08 HV,and the tensile strength is 538 MPa,which is 15%higher than that of the sample without heat treatment.