| The density of magnesium alloy is1.75-1.90g/cm3, about1/4steel,2/3Al, is thelightest engineering materials. With high specific strength and stiffness, It is betterthan steel and aluminum, with great prospects for development. However, due to themagnesium alloy has lot of disadvantages,like low corrosion resistance, poorprocessing of performance, low modulus of elasticity, creep resistance,Poor strengthat high temperatures and high shrinkage rate, it will limit the application ofmagnesium alloys. In order to improve the many shortcomings of magnesium alloys,Rare earth as the main alloying elements or micro-alloying elements are being widelyused in magnesium alloys. According to the study showed that t adding rare earthelements Y, can effectively improve the alloy microstructure and improve themechanical properties of the alloy.In this paper, high-energy ultrasound was used to prepared Rare earth alloy anduse it as a study of Y effect of AZ91magnesium alloy.The study shows that when therare earth Y add into AZ91magnesium alloy, its microstructure became much finer.Because when the Y add into magnesium alloy, Y would make reaction with Alpriority to form needle phase Al2Y. Al2Y phase enriched in the interface and formedcomposition undercooling layer, which inhibited α-Mg phase to continue to grow up,so that it can refine the grain. when the content of rare earth Y up to2.0%, themechanical properties of AZ91magnesium alloy is best. The tensile strengthincreased from312.26MPa to365.91MPa, improved by17.2%; extension rate of3.3%up to11.2%.The extruded material of AZ91-2.0%Y magnesium alloy treatment at410℃，with the extension of the solution time, when it’s treatment6h，the second phaseparticles can dissolve back into the basic α-Mg solid solution alloy, and theorganization is more uniform and fine; However, when continue to extend thesolution, the organization will begin to grow and the emergence of the Phenomenonof organized burned. The extruded material of AZ91-2.0%Y magnesium alloy after200℃/20h aging treatment,The second phase of β-Mg17Al12precipitation much small organizations which is quantity and uniform，distribution spotty and needle;however, beyond20h aging time，the precipitates organization start coarsening.The extruded material of AZ91-2.0%Y magnesium alloy aging micro-hardnessup106.48HV; tensile strength reached386.67MPa; elongation rate reached12.8%.the analysis of ensile fracture morphology under different state extruded AZ91-2.0%Y magnesium alloy and the reason. Investigate the influence of Al2Y to the broken ofalloy particles, so the Al2Y particulate can be a good strength and ductility party asreinforcing material.The effect of rare earth Y，holding time and holding temperature on microstruc--ture evolution of AZ91magnesium alloy in semi-solid state were investigated byusing metallurgical microscope. The results show that yttrium contributes to refinethe alloy’s organization, It hinders proliferation of the particles of the solid phase,slows the Ostwald ripening and make the microstructure of alloy grains morespheroidizing. Added2.0%Y, The Semi-solid microstructure of magnesium alloy isthe most fine and round. With the extension of holding time,The microstructure ofalloy changed from large block into homogeneous spherical. During the increasing ofholding temperature, the serious dendritic in the microstructure of the initial cast alloyturned into semi-solid non-dendritic and the evolution includes coarsening, microstru--cture separation and spheroidizing. However, when the holding temperature is muchhigher or the holding time is much longer, the spherical structure is susceptible togrow up. In addition，the best semi-solid structure for semi-solid-forming can beobtained at570℃and the holding time30min. |
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