| With the rapid development of the aerospace, automobile, defense, high technologyand other fields in our country, the requirements for the comprehensive properties of thematerials are higher and higher. Aluminum matrix composites reinforced with ceramicparticles have been a hot research issue in recent years because of their excellent propertiessuch as low density, high tensile strength, high elastic modulus, etc. Generally, the smallerthe ceramic particle size is, the better the matrix is enhanced, therefore, the fabrication ofaluminum matrix composites reinforced with nano-sized ceramic particles have been animportant development direction. However, because large surface-to-volume ratio of thenano-sized ceramic particles and their poor wettability with the metal matrix, it is difficultto obtain uniform dispersion of nano-sized ceramic particles in the matrix which severelydecreases the properties of the composites and limits their extensive application. At present,the investigations about improving the dispersion of nano-sized ceramic particles in thematrix and interface bonding are still problems to be solved in the world. On the other hand,it is lacking in the researches on the elevated temperature properties of the composites,which seriously affected their applications in the high temperature working conditions inaerospace. So the studies of the microstructures, room temperature and high temperaturetensile properties of aluminum matrix composites reinforced with nano-sized ceramicparticles are very important.In this paper, we fabricated the nano-sized SiCp/Al2014composites successfully bystirring casting, and investigated the effect of the pre-dispersed processing of nano-sizedSiCp on the microstructures and tensile properties of SiCp/Al2014composites. The effect of the content of the nano-sized SiCp on the microstructures, room temperature and hightemperature tensile properties of the nano-sized SiCp/Al2014composites which made bythe addition of master alloys was also investigated in detail. The influence mechanisms ofnano-sized SiCp reinforce Al2014alloys were revealed preliminarily. The effect of surfacenickel plating of nano-sized SiCp on the microstructures, room temperature and hightemperature tensile properties of the composites was investigated and the influencemechanism has been also revealed. The results are list as follows:(1) The pre-dispersed processing of nano-sized SiCp can significantly improve thedispersion of nano-sized SiCp in the matrix. The effect of the ball millingpre-dispersed processing of nano-sized SiCp on the refinement of the composites’.-Aldendrites and the improvement of the tensile strength is more significant than the wetmixing processing of nano-sized SiCp.a) It is revealed that the cast3wt.%nano-sized SiCp/Al2014composite prepared byball milling pre-dispersed possesses the best tensile properties, of which the yieldstrength(220MPa), ultimate tensile strength(410MPa) and fracture strain(6.3%) are10MPa,45MPa and0.8%higher than those of the cast3wt.%nano-sizedSiCp/Al2014composite prepared by wet mixing, because during the ball millingpre-dispersed process, the nano-sized SiCp clusters were broken up drasticallywhich can improve the dispersion of nano-sized SiCp in the metal liquid.b) The yield strength, ultimate tensile strength and fracture strain of the cast5wt.%nano-sized SiCp/Al2014composite prepared by ball milling pre-dispersed are190MPa,362MPa and5.4%, which are lower than those of the cast3wt.%nano-sized SiCp/Al2014composite, because more and more particles gatheredwhen the content of SiCp increased, which leads to more agglomeration of SiCp.(2) The.-Al dendrites sizes of the nano-sized SiCp/Al2014composites fabricated byadding the nano-sized SiCp-Al master alloys are smaller than those of Al2014matrixalloy. The refinement of.-Al dendrites is more significant after using the Ni coatednano-sized SiCp as reinforcements.a) The sizes of.-Al dendrites in the cast microstructures of1wt.%,2wt.%and3wt.% (nominal contents) nano-sized SiCp/Al2014composites are refined from~200Pmof the Al2014matrix alloy to~100Pm,~80Pm and~75Pm, respectively. After hotextrution, The sizes of.-Al dendrites of1wt.%,2wt.%and3wt.%nano-sizedSiCp/Al2014composites are~60Pm,~45Pm and~28Pm, respectively.b) The sizes of.-Al dendrites of1wt.%,2wt.%and3wt.%(nominal contents) Nicoated nano-sized SiCp/Al2014composites are refined from~200Pm of theAl2014matrix alloy to~83Pm,~54Pm and~45Pm, respectively. After hotextrution, The sizes of.-Al dendrites of1wt.%,2wt.%and3wt.%Ni coatednano-sized SiCp/Al2014composites are~57Pm,~32Pm and~21Pm, respectively.c) The corresponding crystal mismatch (6.89%) of E–SiCp and.-Al on the (111)plane is smaller than the critical value of the lattice-matching principle forheterogeneous nucleation, therefore, E–SiCp can act as heterogeneous nuclei,which lead to the refinement of the.-Al dendrites. On the other hand, thenano-sized SiCp in the grain boundary and the interdendritic hinder the growth of.-Al dendrites, which also plays a role of.-Al dendrites refinement. The Nicoated on the surface of nano-sized SiCp promotes the wettability between SiCpand.-Al, improves the dispersion of nano-sized SiCp and makes more nano-sizedSiCp act as heterogeneous nuclei of.-Al.(3) With the increasing nano-sized SiCp content from1wt.%to3wt.%, the yield strengthand ultimate tensile strength of the nano-sized SiCp/Al2014composites increases, thefracture strain decreases. The tensile properties of composite materials are furtherimproved using the Ni coated nano-sized SiCp as reinforcements.a) It is revealed that the2wt.%nano-sized SiCp/Al2014composite possesses the besttensile properties in the1wt.%,2wt.%and3wt.%(nominal contents) nano-sizedSiCp/Al2014composites, of which the room temperature,180and220hightemperature yield strength and ultimate tensile strength are373MPa and527MPa,325MPa and360MPa,235MPa and269MPa, which increase by22.7%and13.8%,25%and16.1%,14.6%and12%, respectively, compared to those of the Al2014matrix alloy (304MPa and463MPa,260MPa and310MPa,205MPa and240MPa), the fracture strain are11.5%,14.9%and17.1%lower than those of the Al2014alloy (17.1%,18.1%and19.2%).b) It is revealed that the3wt.%Ni coated nano-sized SiCp/Al2014compositepossesses the best tensile properties in the1wt.%,2wt.%and3wt.%(nominalcontents) Ni coated nano-sized SiCp/Al2014composites, of which the roomtemperature,180and220high temperature yield strength and ultimate tensilestrength are425MPa and563MPa,350MPa and386MPa,268MPa and303MPa,which increase by39%and21.6%,34.6%and24.5%,30.7%and26.3%,respectively, compared to those of the Al2014matrix alloy, the fracture strain are11.2%,12.8%and15.4%lower than those of the Al2014alloy.(4) The influence mechanisms of the Ni uncoated/coated nano-sized SiCp on the strengthof Al2014matrix alloy are the grain refinement strengthening and Orowanstrengthening, with the last mechanism being the most significant one, especially athigh temperature. The Ni coated on the surface of nano-sized SiCp improves thewettability and the interface bonding strength between SiCp and.-Al, reduces thepossibility of interfacial debonding, which lead to the further improved in the tensileproperties of composites.(5) In conclusion, the3wt.%Ni coated nano-sized SiCp/Al2014composite possesses thebest tensile properties, of which the room temperature,180and220hightemperature yield strength, ultimate tensile strength and fracture strain are425MPa,563MPa and11.2%,350MPa,386MPa and12.8%,268MPa,303MPa and15.4%. |
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