Study On The Microstructure And Tensile Properties Of Nano-SiC_p Reinforced A356 Aluminum Matrix Composites

Particle reinforced aluminum matrix composites（PAMC）have light quality,high specific stiffness,high specific strength,good plasticity,high fatigue limit,high temperature and corrosion resistance,and can greatly adapt to the needs of the development of modern technology.Compared with the micron-particle reinforced aluminum matrix composites,reinforced by nano-ceramic particles can not only significantly improve the strength of the material,but also obtain equivalent or even higher plasticity than matrix alloy.Therefore,nanoparticle reinforced aluminum matrix composites（NPAMC）have become the research focus of metal matrix composites.However,the large specific surface area of nano-particles,the tendency to agglomerate,and the poor wettability of the ceramic particles and the metal matrix are the main difficulties by the casting method and have not been solved very well.Therefore,this paper presents the preparation of nano-SiC_p/A356 aluminum matrix composites by combining SiC_p preoxidation,high energy ball milling and ultrasonic vibration.The effect of SiC_p preoxidation on the microstructure of the composites was investigated.The dry high energy ball milling was used to prepare composite granules.The advantages and disadvantages of fixed-speed and variable-speed ball milling and the effect of different nano-SiC_p contents on the distribution in composite granules were studied.The effect of different ultrasonic vibration parameters on the distribution of nano-SiC_p and the microstructure and mechanical properties of the composites was also researched.The effect of Sr on the microstructure and mechanical properties of nano-SiC_p/A356 composites with different SiC_p content was investigated.Meanwhile,the influence of nano-SiC_p on the aging behavior of composites was studied.The size of the composite granules can reach millimeter,nano-SiC_p can be uniformly distributed in the composite granules,the interface is well bonded,and no harmful phase Al₄C₃ is found by using variable-speed high-energy ball milling process.Increasing the content of nano-SiC_p particles decreases the degree of uniform dispersion of the particles.When the nano-SiC_p content does not exceed 6wt%,the nano-particles in the composite granules can be evenly distributed.Nano-SiC_p can be successfully added to the aluminum melt through SiC_p/Al composite granules that are used as carriers,which effectively avoids the problem of poor wettability between the ceramic particles and the matrix alloy.Through the analysis of the microstructure of the composites,the preoxidation of SiC_p can effectively prevent the formation of interface brittle phase Al₄C₃ in the SiC_p/A356 composite.That ultrasonic vibration applied to the nano-SiC_p/A356 composite melt can significantly improve the nano-SiC_p distribution and refine the solidified microstructure.When the temperature of ultrasonic vibration is 700℃and the time is 3min,the primaryα-Al and eutectic Si are obviously refined.Meanwhile,the nano-SiC_p distributed uniformly around eutectic Si and the composite obtains the best mechanical properties.Through the analysis of the effect of different SiC_p contents on the nano-SiC_p/A356 composites,it shows that with the increase of SiC_p content,the morphology of primaryα-Al grains transforms from coarse dendrites to rose-like crystals,the grain is refined and the eutectic Si becomes gradually shorter.With the increase of SiC_p content,the as-cast mechanical properties of nano-SiC_p/A356 composites have a greater improvement than that of the matrix alloy.When the content of SiC_p is 2wt%,its tensile strength,yield strength and elongation are 259MPa,144MPa and 5.3%respectively,which are 19.5%,69.4%and 15.2%higher than that of matrix alloy.With the addition of Sr,the eutectic Si in A356 and its composites have been refined to some extent.Since Sr is easy to react with O on SiC_p surface and then consumed,the effect of Sr on the aluminum matrix composites is gradually weakened with the increase of nano-SiC_p content.By comparing the aging behavior of A356 and 1wt%nano-SiC_p/A356composites,it is found that the addition of nano-SiC_p can accelerate the aging precipitation and shorten the peak aging time.In peak aging condition,the hardness of 1wt%nano-SiC_p/A356 composites reaches 114.3HV,which is 10.7HV higher than that of matrix alloy.Meanwhile,the tensile strength,yield strength and elongation of 1wt%nano-SiC_p/A356 composites are 335MPa,226MPa and 5.6%respectively,which are 19.6%,17.7%and 5.7%higher than that of the matrix alloy in T6 condition.