| In this paper,the Mg-6Zn-0.5Cu-0.2Zr and Mg-6Zn-0.5Cu-0.2Zr-0.5(Cr,Ca)alloys are used under the pressure of 2 GPa,4 GPa and 6 GPa using CS-1V six-face hydraulic press.A high pressure solidification experiment was carried out.SEM/XRD and other analytical methods were used to study the solidification microstructure and solidification microstructure refinement mechanism of Mg-6Zn-0.5Cu-0.2Zr alloy under the action of GPa high pressure and composite addition(Cr,Ca).The mechanical properties and mechanical properties of room temperatrure were improved.The experimental results are as follows:Under the high pressure of GPa,the average size of the "dendritic group" of Mg-6Zn-0.5Cu-0.2Zr alloy is gradually reduced from 344 μm under normal pressure to 110μm and 59 μm under 2 GPa and 6 GPa.The number of crystal nuclei on the area is increased from 19 under undermospheric pressure to 65 and 129 under 2 GPa and 6 GPa,The intercrystalline second phase is gradually connected to the network by the layered eutectic structure under normal pressure.The distribution becomes 2 GPa,6 GPa intermittently distributed in the form of lower particles or thin bands.the solid solubility of Zn and Cu in the munderrix is gradually increased from 1.6%and 0.11%under normal pressure to 2 GPa,3.58%and 0.16%,4.80%and 0.21%under 6 GPa.After compound addition(Ca,Ca),the average size of the "dendritic group" of the experimental alloy was gradually reduced from 262μm under normal pressure to 58 μm and 44 μm under 2 GPa and 6 GPa;the number of nuclei per unit area was determined by 31 under normal pressure gradually increased to 98 and 174 under 2 GPa and 6 GPa;the second phase of the intergranular phase was gradually connected into a network by a block-like structure with a small amount of lamellar structure on the surface under normal pressure.It becomes a "layered eutectic" microstructure with a discontinuous distribution of 2 GPa and 6 GPa,and a solid island shape.the solid solubility of Zn and Cu in the matrix was gradually increased from 1.60%and 0.11%under normal pressure to 2 GPa,3.58%and 0.16%,4.80%and 0.21%under 6 GPa.After compound addition(Cr,Ca),the solid solubility of Zn and Cu in the matrix is gradually increased from 3.63%and 0.19%under normal pressure to 2 GPa,5.68%and 0.28%,6.23%and 0.55%under 6 GPa.It can be seen that the high pressure solidification significantly refines the solidification structure of the alloy,greunderly improves the morphology and distribution of the second phase between the crystals,and significantly increases the solid solubility of the solute atoms in the munderrix.After compound addition(Cr,Ca),the microstructure of the high pressure solidification experimental alloy is further refined,and the solid solubility of the solute atoms in the matrix is increased.Under normal pressure,the mismatch of MgZn2 phase,Mg2Ca phase,Cr2Zr phase and Mg matrix low index surface is more than 15%,which are not effective heterogeneous nucleus of Mg.When the solidification pressure increases to 5 GPa,there are very similar positions between the MgZn2 phase,the Mg2Ca phase,the Cr2Zr phase and the α-Mg,and the mutually parallel Kikuchi zone;the orientation relunderionship between the MgZn2 phase and the surrounding α-Mg matrix is:[1100]MgZn2//[1100]α-Mg,(0001)MgZn2//(0001)α-Mg;between Mg2Ca phase and its surrounding α-Mg munderrix The orientation reluationship is:[0001]Mg2Ca//[1 2 10]α-Mg,(000 1)Mg2Ca//(0001)α-Mg;orientation between Cr2Zr phase and its surrounding α-Mg matrix The relationship is:[110]Cr2Zr//[1120]α-Mg,(110)Cr2Zr//(0001)α-Mg,(110)Cr2Zr//(0001)α-Mg.Therefore,the new phase(Mg2Ca phase,Cr2Zr phase)produced by the MgZn2 phase and the composite addition(Ca,Ca)is Mg-6Zn-0.5Cu-0.2Zr-0.5(Cr,Ca)when solidified(5 GPa)under high pressure.An effective heterogeneous nucleus substrate of theα-Mg crystal of the inner portion of the alloy.Under normal pressure,the σb,σs and δ.of the Mg-6Zn-0.5Cu-0.2Zr alloy are 170 MPa,160 MPa and 11%,respectively.After solidification under 2 GPa、6 GPa,the room temperature properties were σb,σs and δ of 320 MPa,280 MPa and 18.4%,respectively,430 MPa,370 MPa and 14%.After compound addition(Cr,Ca),the σb,σs and δ of Mg-6Zn-0.5Cu-0.2Zr-0.5(Cr,Ca)alloy are gradually increased from 241 MPa,216 MPa and 14.8%under normal pressure.2 GPa,409 MPa,362 MPa and 21%under 6 GPa,520 MPa,460 MPa and 16.5%.That is,under the action of high pressure of GPa,the composite addition(Cr,Ca)can greatly improve the room temperature compression performance of the alloy,and the strong plastic product of the alloy under 6 GPa is as high as 8580 MPa.%.When the Mg-6Zn-0.5Cu-0.2Zr alloy is pressed from normal pressure to 2 GPa,the contribution runderio of fine grain strengthening,solid solution strengthening and second phase strengthening to strength is 10%,75%,and 15%,respectively.The rate is the largest,which is the main strengthening mechanism.When 2 GPa-6 GPa,the contribution ratio of the three to the intensity is 10%,63%,and 27%,respectively.Solid solution strengthening is the main strengthening mechanism.After compound addition(Cr,Ca),the contribution ratio of fine grain strengthening,solid solution strengthening and second phase strengthening to strength is 14%,67%,and 19%,respectively,under atmospheric pressure to 2 GPa;The mechanism is mainly solid solution strengthening.2 GPa-6 GPa,the contribution runderio of the three to the intensity is 6%,33%,61%;therefore,the second phase strengthening becomes the main strengthening mechanism;and as the pressure increases,the second phase strengthening contribution rate increases gradually.It can be seen that high pressure solidification and composite addition(Cr,Ca)change the main strengthening mechanism of the alloy. |
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