Study On Microstructure, Properties And Deformation Behavior Of Mg₉₆Zn₁Y₃ Alloys Doped With Si

With the entrance to 21st century, the resource and environment problems have become the principle problems in the sustainable development of human beings. Therefore the trends of the industrial development all over the world can be reduced to the saving of energy and resource, what is more , the pursuit of natural productions. The study and development on light castings has been an important research field and developing direction, with the rapid development of automotive industry. Magnesium alloys are the lightest structural metal alloys, which have many excellent and unique properties, such as low density, high specific strength and stiffness, good damping and shock absorption, easy processing and castability, high heat and electrical conductivity, excellent electromagnetic shielding capability, as well as a good recovery capability, etc. So more and more magnesium alloy products have been used in automotive, communication apparatus and aerospace industries. Consequently, it is considered that magnesium alloys are the most worthy and exploitative"natural engineering materials"with greatly potential application in the century.Mg-Zn-Y alloy with the chemical composition of Mg-1～3at%Zn-2～6at%Y reveals excellent mechanical properties. The Mg₉₆Zn₁Y₃ alloy were achieved by warm extrusion of gas-atomized powders, which has a high yield strength of 590 MPa . In the present work, as-cast and hot rolled Mg₉₆Zn₁Y₃ alloys with Si addition were prepared. The microstructure and mechanical properties , especially friction and wear characteristics of the alloys were studied, which will offer theoretical foundations for extensive applications of magnesium alloys.At first, the composition and the phase component of the Mg₉₆Zn₁Y₃—xSi as cast alloys were determined by EDS and the XRD analysis, and then the microstructure was studied. The phase analysis indicated that, Mg₉₆Zn₁Y₃ and Mg₉₆Zn₁Y₃—0.7Si as cast alloys consist of the substrateα-Mg solid solution and strengthened Mg12YZn phase.Mg₉₆Zn₁Y₃—1.5Si as cast alloy consists ofα-Mg, Mg12YZn and the unknown phase which contain Mg,Y,Si element. The mechanical properties of the as cast Mg₉₆Zn₁Y₃—xSi alloys were studied. The ultimate tensile strength, yield strength and elongation to failure of the as cast Mg₉₆Zn₁Y₃ alloy were higher than Mg₉₆Zn₁Y₃—0.7Si and Mg₉₆Zn₁Y₃—1.5Si alloys ,which reveals excellent mechanical properties. The mechanical properties of the as cast Mg₉₆Zn₁Y₃—1.5Si alloy were the worst of the three.The friction and wear performances of as cast Mg₉₆Zn₁Y₃—xSi as cast alloys were studied. Dry sliding wear tests were performed using a MG-2000 type pin-disc wear apparatus. The transition of Mg₉₆Zn₁Y₃ alloys from mild wear to severe wear was later than Mg₉₆Zn₁Y₃—0.7Si and Mg₉₆Zn₁Y₃—1.5Si alloys. The wear rate of the alloys increase with increasing load . At low load(under 160N), the wear rate of Mg₉₆Zn₁Y₃ and Mg₉₆Zn₁Y₃—0.7Si alloys were almost the same, lower than that of Mg₉₆Zn₁Y₃—1.5Si alloys.At higher loads, wear rate of Mg₉₆Zn₁Y₃ were lower than that of Mg₉₆Zn₁Y₃—0.7Si and Mg₉₆Zn₁Y₃—1.5Si alloys. The friction coefficients of the Mg₉₆Zn₁Y₃—xSi alloys decrease with increasing load and were indistinctive. By means of SEM observations on wear surfaces were carried out. We also compare the wear properties of as cast Mg₉₆Zn₁Y₃ alloy with the AZ91 alloy , conclude that the friction coefficients and wear rate of the Mg₉₆Zn₁Y₃ alloy were lower than that of the AZ91 alloy ,especially at high loads.The bulk temperatures were calculated by some formulas, the temperature of Mg₉₆Zn₁Y₃ alloys were lower than AZ91 alloys, and then the difference in wear mechanism and performance of the alloys were discussed.The mechanical properties of the hot rolled Mg₉₆Zn₁Y₃—xSi alloys were studied. The ultimate tensile strength, yield strength and elongation of the rolled Mg₉₆Zn₁Y₃ alloy were higher than Mg₉₆Zn₁Y₃—0.7Si and Mg₉₆Zn₁Y₃—1.5Si rolled alloys,which reveals excellent mechanical properties. What's more, the mechanical properties of rolled Mg₉₆Zn₁Y₃ alloys at different test temperatures were studied, they still have good tensile properties at higher test temperatures (250℃). The mechanical performance and fracture characteristic was analyzed, simultaneously the explanation of strengthening mechanism of the alloys was made.