Study On Preparation And Grain Refining Efficiency Of Al-Zr-B Alloy For Magnesium Alloy

Abstract:Magnesium alloys, which can meet the demands of lightweight and low energy consumption, are receiving increased attention in aeronautical, automotive, electric and automobiles. However, the application of magnesium alloys is restricted seriously because of their low strength, plastic deformation capability, creep resistance and high-temperature performance. Grain refinement is important for magnesium alloy to improve their strength and plastic deformation capability. In this thesis, Al-Zr-B master alloys were fabricated by melt reation method and the effects of B/Zr mole ratio, synthesis temperature, high-intensity ultrasound and extrusion on the microstructure, phase constituent and grain refining performance of Al-Zr-B master alloys were studied. The main work and research results can be summarized as follows:(1) The influences of B/Zr mole ratio on microstructure and grain refining performance of Al-Zr-B master alloys were systematic studied. The results show that the phase constituent is Al+ZrB2+ZrAl3when B/Zr ratio is about1while it is Al+ZrB2when B/Zr ratio is about2and3. The grain refining experiments show that only the master alloy containing Al and ZrB2phases has grain refining efficency and it is best when B/Zr ratio is about3(Al-5Zr-1.78B), The grain size of AZ91D alloy are decreased from328μm to145μm by adding0.2wt%Al-5Zr-1.78B master alloy.(2) The influences of synthesis temperature on microstructure and grain refining performance of Al-5Zr-1.78B master alloys were systematic studied. The results show that the yield of Zr and B elements are most when the synthesis temperature is850℃. Meanwhile, the second phase is not easy to reunion. The grain refining experiments show that the Al-5Zr-1.78B master alloy synthesized at850℃has excellent refining efficency and it is best when the addition is0.6wt%. The grain size, tensile strength and elongation of AZ91D alloy are108μm,200MPa and3.94%, respectively, which are increased by67.07%,29.03and 30.3%, respectively.(3) The influences of high-intensity ultrasound and extrusion on microstructure and grain refining performance of Al-5Zr-1.78B master alloys were studied. The results show that the high-intensity ultrasound and extrusion can significantly smash the agglomeration of ZrB2particles and make them more tiny and uniformly distribute. Thus the grain refining efficency is improved. The grain size, tensile strength and elongation of AZ91D alloy are80μm,215MPa and4.38%, respectively when adding0.6wt%Al-5Zr-1.78B master alloys prepared by ultrasonic vibration, which are increased by75.61%,38.71%and42.21%, respectively, while they are63.7μm,225MPa and4.91%by adding0.4wt%Al-5Zr-1.78B master alloys prepared by extruding, which are increased by80.58%,45.16%and59.42%, respectively.