Fabrication And Mechanical Properties Of Nano-sic Particulates Reinforced Magnesium Matrix Composites By Powder Metallurgy Method

Nano-SiC particulates(n-SiC_p)have good potential as reinforcement in fabrication of metal matrix composites(MMCs)because of the small particle size,high modulus,high hardness,high strength and low density.Mg-8Al-Sn(AT81)shows both good strength and plasticity at the room and high temperature as the lightweight metal matrix.However,there are many problems in n-SiC_p reinforced magnesium metal matrix composites to date.The problems are mainly concentrated in the following aspects,(i)The n-SiC_p tend to agglomerate because of the fine particulate size and high surface energy of nano-SiC particulates,leading to the difficulty of homogeneous dispersing in the composites.(ii)To date,there has been relatively little research on interface between n-SiC_p and matrix,and also no systematic study on the influence of the interfacial product on the mechanical properties of the composites.To solve the above problems,solvent dispersion and direct ball milling process were used to mix powders sufficiently,and the n-SiC_p/AT81 composites were fabricated by powder metallurgy combined with hot extrusion.In this study,the microstructure and mechanical properties of the Mg-8Al-1Sn composites with different volume fractions of n-SiC_p were investigated.The effects of nano-SiC particulates with different pre-oxidation parameters on the microstructures and tensile properties of n-SiC_p/AT81 composites were investigated.The interface and strengthening mechanisms of n-SiC_p/AT81 composites were studied,which are important to fabricate the metal matrix composites with high performance.The main conclusions are as follows:1)A new method of solvent dispersion combined with mechanical ball milling process was prepared to disperse n-SiC_p in the AT81 matrix;the influences on microstructures of composites reinforced by different volume fractions of n-SiC_p were investigated;the grain size was progressively refined with the increase of n-SiC_p content.2)The influence on mechanical properties of n-SiC_p/AT81 composites reinforced by different volume fractions of n-SiC_p were investigated and results revealed that the optimized volume of n-SiC_p was 0.50%;the 0.2% offset yield strength(YS),ultimate compressive strength(UCS)and fracture strain of 0.5 vol.% n-SiC_p/AT81 composite were 156 MPa,397 MPa and 17.2% at room temperature,which were 108%,41.3% and 41.0% higher as compared to the particulate-free AT81;the 0.2% offset yield strength(YS),ultimate tensile strength(UTS)and elongation(?)of 0.5 vol.% n-SiC_p/AT81 composite were 239 MPa,381 MPa and 8.3% at room temperature,which were 36.6%,19.8% and 84.4% higher compared to the unreinforced AT81 alloy;the purpose of improving mechanical properties was achieved without sacrificing the plastic.3)The “furrow” of n-SiC_p/AT81 composites was relatively shallow and narrow;meanwhile,the wear surface became relatively smooth compared to AT81 alloy;the wear rate of composites decreased with the increase of n-SiC_p addition;The corrosion sensitivity of composites reduced with the addition of n-SiC_p due to finer size and good contact with the interface;meanwhile,the corrosion rate reduced and corrosion resistant performance improved with the n-SiC_p addition;the wear rate at 20 N was 5.05×10-3 mm3/m and corrosion current density was 4.1×10-7 A/cm2.4)The YS and UTS of 0.5 vol.% n-SiC_p-oxi/AT81 further improved by adding pre-oxidized n-SiC_p;the tensile properties of composites were best when pre-oxidation parameter was 800 ?/2 h;the YS,UTS and ? are 255 MPa,393 MPa and 5.8% respectively;however,the YS and UTS of 0.5 vol.% n-SiC_p-oxi/AT81 composites decreased when the pre-oxidation temperature was 1000 ?;it was revealed that the optimal pre-oxidation parameters of n-SiC_p were 800 ?/2 h.5)There was a clean interface with no obvious interfacial products,indicating a good bonding between untreated n-SiC_p and the matrix;it was found that the Mg Al2O4 formed between n-SiC_p and matrix when the n-SiC_p was pre-oxidized at 800 ? for 2 h,while the interface layer was about 1.0 nm in thickness;when pre-oxidation parameter was 1000 ?/2 h,Mg Al2O4 was clearly observed and the thickness of interface between the n-SiC_p and matrix was about 6-7 nm;in conclusion,the formation of an appropriate amount of interfacial product benefited the material's mechanical properties;it revealed that the main strengthening mechanism of the n-SiC_p/AT81 composites was the dislocation strengthening;the Orowan strengthening,grain refinement strengthening and stress transfer from AT81 to the n-SiC_p played supporting roles in strengthening mechanisms by the analysis of microstructure and interface.