Room and High Temperature Properties of Micron-nano Sized (TiCp-TiB2p)/Al-Cu-Mg-Si Composites

Author:Gao Zuo Yang

Supervisor:jiang qi chuan

Database:Doctor

Degree Year:2019

Download:22

Pages:156

Size:10981K

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Compared with the single-phased single micron/nano sized ceramic particles reinforced Al matrix composites,the dula-phased micron-nano hybrid-sized ceramic particles reinforced Al matrix composites exhibit superior room temperature tensile properties,wear resistance and fatigue resistance.Among the ceramic particle reinforcement phases,in-situ TiCp and TiB2p have the advantages of good lattice matching withα-Al,high interface bonding strength with Al matrix,and no reaction with Al matrix to generate harmful interface products.At present,in-situ dual-phased TiCp-TiB2p reinforced Al matrix composite prepared by the melt reaction method and the mixed salt reaction method has the following disadvantages:the residue of reactants is liable to remained;these methods cannot effectively regulate the TiCp-TiB2p size;TiCp-TiB2p possess a large size(>0.5μm)and are easy to cause the agglomeration,which is not conductive to the full play of the TiCp-TiB2p strengthening effects.Therefore,to explore and study the preparation technology of micron-nano sized TiCp-TiB2p reinforced Al matrix composites by using the new in situ methods,study the influence laws and mechanisms of the in situ micron-nano sized TiCp-TiB2p on the room and high temperature properties of the Al matrix composites,have great academic significance and pratical application value for further increasing the room and high temperature performance of Al matrix composites and expanding therir industrial application range.In this paper,(1)for the first time,the in-situ high weight percentage(TiCp-TiB2p)/Al-Cu-Mg-Si composites were fabricated by combustion synthesis of Al-Ti-B4C systems+hot pressing+hot extrusion technology.The influence laws and mechanisms of in situ micron-nano sized high weigth percentage TiCp-TiB2p on the room temperature strength,high temperature strength and ductility and wear resistance of Al-Cu-Mg-Si composites were studied and revealed;(2)for the first time,the minor amount(0.05wt.%,0.1wt.%)of(TiCp-TiB2p)/Al-Cu-Mg-Si composites were prepared by using the micron-nano sized(TiCp-TiB2p)/Al-Cu-Mg-Si master alloy+stir casting+hot extrusion technology.The influence laws and mechanisms of minor amount of micron-nano sized TiCp-TiB2p on the room and high temperature tensile properties,room temperature fatigue properties and high temperature creep behaviors of Al-Cu-Mg-Si alloys were studied and revealed.The mian innovations of this paper are as follows:1)For the first time,the in-situ high weigth percentage micron-nano sized(TiCp-TiB2p)/Al-Cu-Mg-Si composites were successfully fabricated by combustion synthesis of Al-Ti-B4C systems+hot pressing+hot extrusion technology.i)It was found that when the in situ TiCp and TiB2p were synthesized in Al-Ti-B4C system,as the weight percentage of the generated in situ TiCp-TiB2p increased,the percentage of the nano sized TiCp-TiB2p decreased,while that of the submicron sized TiCp-TiB2p increased.The percentages of nano and submicron sized TiCp-TiB2p in the 40 wt.%(TiCp-TiB2p)/Al-Cu-Mg-Si composite were 3.0%and 95.6%,respectively.ii)It was revealed that the room temperature yield strength and tensile strength of the 40 wt.%(TiCp-TiB2p)/Al-Cu-Mg-Si composite were the highest in this study,569 MPa and 704 MPa,respectively,which were 242 MPa and 238 MPa higher than those of the matrix alloy(327 MPa and 466 MPa),but the fracture strain(2.9%)was 8.6% lower than that of the matrix alloy(11.5%).The mechanisms for improving the room temperature strength of composites were:thermal mismatch strengthening,load transfer strengthening,Orowan strengthening and finerθ′precipitation strengthening.iii)It was revealed that the in-situ micron-nano sized TiCp and TiB2p simultaneously increased the high temperature strength and ductility of the Al-Cu-Mg-Si composites.At 573K,the yield strength,tensile strength and fracture strain of the 40 wt.%(TiCp-TiB2p)/Al-Cu-Mg-Si composite were 141 MPa,164 MPa and 31.2%,respectively,which were 60.2%,72.6%and 22.4%higher than those of the matrix alloy(88 MPa,95 MPa and 25.5%),respectively.The mechanisms of high temperature strength and ductility improvement of composites were mainly as follows:(a)micron-nano sized TiCp and TiB2p pinning theα-Al grain boundaries and hindering the dislocation motions;(b)the finerθ’precipitation strengthening.iv)It was revealed that the relative abrasive wear resistance of the in-situ high weight percentage micron-nano sized(TiCp-TiB2p)/Al-Cu-Mg-Si composites were sigficantly improved compared with that of the matrix alloy under different Al2O3sandpaper particle sizes(40μm,23μm,13μm)and different applied loads(5 N,15N,25 N),and the relative wear resistance of 40 wt.%(TiCp-TiB2p)/Al-Cu-Mg-Si composite was 4.17 times higher than that of the matrix alloy under the abrasive particle size of 13μm and applied load of 5 N.The improvement of abrasive wear resistance of the composite is mianly attributed to:the in-situ micron-nano sized TiCp-TiB2p weaken the penetration and ploughing of abrasive particles.2)For the first time,the minor amount(0.05wt.%,0.1wt.%)of(TiCp-TiB2p)/Al-Cu-Mg-Si composites were prepared by master alloy+stir casting+hot extrusion technology.i)It was revealed that during the solidification process,the micron-nano sized TiCp and TiB2p can serve as the effective heterogeneous nucleation sites forα-Al grains,thereby refining theα-Al grains;during the hot extrusion and T6 heat treatment process,the minor amount of micron-nano sized TiCp and TiB2p promoted the recrystallization nucleation ofα-Al grains,and inhibited the growth of the recrystallized grains by pinning grain boundaries;the percentage of fineα-Al recrystallized grains(2.6-5.0μm)in Al-Cu-Mg-Si alloy,0.05wt.%,0.1 wt.%(TiCp-TiB2p)/Al-Cu-Mg-Si composites was 29.1%,44.9%and 46.0%,respectively;during the solution treatment in the T6 heat treatment,the decreasedα-Al grain size shortened the diffusion distance of Cu,Mg and Si atoms into the interior ofα-Al grains,promoted the uniform distribution of Cu,Mg and Si atoms in the matrix,therefore,a larger number of finer and more uniformly distributedθ’and Q’precipitates were precipitated during aging treatment.ii)It was revealed that the incorporation of minor amount of micron-nano sized TiCp-TiB2p simultaneously increased the room temperature strength and ductility of the Al-Cu-Mg-Si alloys.The room temperature yield strength,tensile strength and uniform elongation of 0.05wt.%(TiCp-TiB2p)/Al-Cu-Mg-Si composite were 310 MPa,471MPa and 22.8%,respectively,which were 32 MPa,36 MPa and 3.8%higher than those of the matrix alloy(278 MPa 435 MPa and 19.0%).The mechanisms of simultaneous improvement on room temperature strength and ductility were mainly as follows:grain refinement strengthening,θ’and Q’precipitation strengthening,and Orowan strengthening of nano-sized TiCp and TiB2p.iii)It was revealed that the addition of minor amount of micron-nano sized TiCp-TiB2p increased the fatigue resistance of Al-Cu-Mg-Si alloy significantly.The fatigue limit strength of 0.1wt.%(TiCp-TiB2p)/Al-Cu-Mg-Si composite was 125 MPa,which was 31.6%higher than that of the matrix alloy(95 MPa).The improvement of fatigue resistance of composites at room temperature is mainly attributed to:(a)α-Al grain refinement:On the one hand,the grain orientation became more complicated,and the initiation of the fatigue crack souce was suppressed;on the other hand,the fatigue crack propagation path was more tortuous,thereby reducing the fatigue crack growth rate.(b)the micron-nano sized TiCp-TiB2p and finerθ’and Q’precipitates hindered the dislocation slip of crack tip,resulting in the reduced fatigue crack growth rate.iv)It was revealed that the addition of minor amount of micron-nano sized TiCp-TiB2pp simultaneously and significantly increased the high temperature strength and ductility of Al-Cu-Mg-Si matrix alloys.At 493 K,the yield strength,tensile strength and uniform elongation of 0.1 wt.%(TiCp-TiB2p)/Al-Cu-Mg-Si composite were 279 MPa,366 MPa and 10.6%,respectively,which were 24 MPa,48 MPa,and 2.1%higher than those of the matrix alloy(255 MPa,318 MPa,and 8.5%).v)It was revealed that the addition of minor amount of micron-nano sized TiCp-TiB2p effectively increased the apparent activation energy and threshold stress of Al-Cu-Mg-Si alloy,thereby improving the high temperature creep resistance.The creep rupture time of 0.05 wt.%(TiCp-TiB2p)/Al-Cu-Mg-Si composite(21.4h)was 18.9 h longer than that of Al-Cu-Mg-Si matrix alloy(2.5 h)at 473 K under 220 MPa.The steady state creep rate of the Al-Cu-Mg-Si alloy was 7.9 times higher than that of the0.05 wt.%(TiCp-TiB2p)/Al-Cu-Mg-Si composite at 473 K under 140 MPa.vi)It was revealed the mechanism of high temperature strength and ductility and high temperature creep resistance improvement were mianly as follow:(a)precipitation strengthening of finerθ’and Q’precipitates;(b)pinning effects of micron-nano sized TiCp-TiB2p distributed at the grain boundary on the grain boudnaries;(c)hindering the dislocation motions of TiCp-TiB2p distributed in the interior ofα-Al grains.The results obtained in this paper provides a new technical idea,experimental basis and theoretical reference for the development and preparation of micron-nano sized ceramic particles reinforced Al matrix composites with high room temperature and high temperature mechanical properties,room temperature fatigue properties and high temperature creep resistance.