| High silicon aluminum alloy is widely used in various automotive parts and electronic packaging materials because of its excellent thermal expansion and friction and wear properties.However,the coarse,complex and irregular polyhedral primary Si and large flake-like eutectic Si structure in its structure seriously reduce the performance of the material.The refinement and modification effect of the silicon phase will directly determine the performance of the material.How to obtain the fine Small and regular bulk primary Si and fine fibrous eutectic Si are the focus of research.Due to the bottleneck and toxic effect of chemical Modificators,the refinement and modification of silicon phase of high silicon aluminum alloy are faced with many challenges.Therefore,in this paper,?-Al2O3nanoparticles combined with high-energy ultrasonic treatment device are used to add them to Al-20Si alloy to realize the refinement and modification of Si phase by nanoparticles,and the mechanism analysis is carried out.It is found that the effect of nanoparticles on primary Si and eutectic Si is significant,the growth process has physical inhibition,significantly reduce the nucleation and supercooling of primary Si and it can possibly be used as heterogeneous nucleation core of primary Si.With the increase of the amount of?-Al2O3 nanoparticles,the primary Si size is refined from 66.2?m to 26.7?m,the size refining efficiency has reached59.7%,and the aspect ratio has also decreased from 2.5 to 1.54,improving the morphology and distribution of primary Si on the substrate,and the length of eutectic silicon has also decreased from 67.5 The hardness,tensile strength and elongation of the material were increased from 57.1HV,102.4MPa and 0.6%to 88.1HV,152.8MPa and 1.72%respectively.The thermal expansion property of the material was also significantly reduced.The wear rate of the material was reduced from 5.30×10-3mm/m to2.26×10-3mm/m,which was 57.4%lower.The wear mechanism also changed from peeling wear to adhesive wear and abrasive wear.At the same time,the effect of cooling rate on the nano particle reinforced Al-20Si composite was studied.It was found that at the high cooling rate of 110K/s,the nano particle still had a significant refining effect on the primary silicon.At this time,the average size of the primary Si of Al-20Si composite reached a minimum of 15.8?m,the aspect ratio was 1.28,the length of the eutectic silicon was 4.6?m,and the refining efficiency of the primary Si reached to 37.8%at 15K/s,the refining efficiency of eutectic Si reaches80.3%,and it is found that nano particles can induce more twin branches of eutectic Si at high cooling rate,which makes the eutectic Si present fibrous structure.At 110K/s cooling rate,The mechanical properties of Al-20Si composites are the highest,and UTS and elongation are 178.5MPa and 2.4%,respectively. |
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