The Microstructure And Mechanical Properties Of Mg-based Glass Matrix Composites

As the lightest structural material, the ordinary Mg alloy has been applied in automobileindustry, electronics, aerospace industry and other fields. However, the application scope ofMg alloy is limited due to its low strength and poor corrosion resistance. For Mg-based bulkmetallic glasses (BMGs), the strength and corrosion resistance have been improved, but theyare brittle. The Mg-based BMG matrix composites, by contrast, have better comprehensivemechanical properties, which are the research hotspot in this field.Based on the Mg-Cu-Y alloy with high glass forming ability, the relationship betweenmicrostructure and mechanical properties for BMG matrix composite, the relationship betweenalloying element addition and phase separation, the formation mechanism of two-phaseglasses were investigated by adding Be, Ti and Zr alloying elements into the alloy. In addition,based on the Mg-Ni-Zn-Y BMG matrix composite with long period stacking order (LPSO)structure, the phase composition, spatial structure and fracture mechanism of the alloy weresystematically researched. The main experimental results are as following:The (Mg0.585Cu0.305Y0.11)100-xBex(x=3,5,7,10) alloys with3mm in diameter werefabricated by conventional Cu-mould casting method. The Cu-Y-Be second phase isdistributed in the alloys because of Be addition. The size and the quantity of the second phaseare increased with the increase of Be content. The compressive fracture strengths of the alloysare866,954,1086and953MPa, respectively, presenting a trend of first increase and thendecrease. It is known by using TEM and selected area electron diffraction analyses that phaseseparation was occurred in (Mg0.585Cu0.305Y0.11)95Be5alloy. The second phase of the alloy isconsisted of Cu-Y-Be amorphous phase and CuY crystalline phase. The compressive fracturestrengths of the samples with1,2and3mm in diameters for (Mg0.585Cu0.305Y0.11)95Be5alloyare959,955and954MPa, respectively, indicating the sample-size independence ofcompressive fracture strength.The (Mg0.585Cu0.305Y0.11)90Ti10and (Mg0.585Cu0.305Y0.11)90(Ti0.7Be0.3)10alloys wereinvestigated. A number of white CuTi crystalline phases are distributed in these two alloys.The second phase in the latter, which contain some amorphous phase, is bigger and more thanthat in the former. The compressive fracture strengths of these two alloys with3mm in diameter are798and1008MPa, respectively, which are increased by about17%and48%than that of Mg58.5Cu30.5Y11alloy. Compared with15.5%strength ratio between the maximumand the minimum fracture strength values for Mg58.5Cu30.5Y11alloy, the values5.1%and4.8%for the (Mg0.585Cu0.305Y0.11)90Ti10and (Mg0.585Cu0.305Y0.11)90(Ti0.7Be0.3)10alloys indicate thattheir strength reliability is improved by Ti and Ti70Be30addition.The microstructure and mechanical properties for the(Mg0.585Cu0.305Y0.11)97(Zr0.35Ti0.3Be0.275Cu0.075)3alloy with3mm in diameter were investigated.The Zr-rich amorphous spherical phase distributed in the Mg-rich glassy matrix was observedby using SEM. Based on the TEM and selected area electron diffraction analyses, it isindicated that the phase separation was occurred in the alloy during the solidification process,forming the Mg-rich and Zr-rich two-phase glasses. The compressive fracture strength, elasticstrain and plastic strain of the alloy are1026MPa,2.2%and0.3%, respectively, indicating theimprovement of the mechanical properties for the alloy. The improvement of compressivefracture strength and the formation of plastic deformation for the BMG are attributed to theshear-band propagation, multiplication and interaction caused by the hard Zr-rich amorphousspherical phase.The Mg81Ni8Zn5Y6BMG matrix composite containing LPSO phase with2mm indiameter was investigated. The alloy is consisted of Mg-rich amorphous matrix phase,Mg12ZnY crystalline phase, ?-Mg phase and a diamond-cubic quaternary metastable phase.The Mg12ZnY is a14H-type LPSO phase, which is distributed in the glass matrix as net-liketexture. The fracture strength, yield strength and plastic strain of the alloy are678MPa,510MPa and12.9%, respectively. Six stages of fracture process for the alloy can be outlined asstress concentration, embryonic shear bands formation, mature shear bands formation, shearbands propagation, shear band multiplication and shear-off.