Study On Microstructure And Mechanical Properties Of The Quasicrystal Reinforced Mg-Zn-Y-Zr Alloy

Magnesium alloys are the lightest structural material in engineering application,known as the most promising green engineering material in the twenty-first Century,which has the advantages of low density,high specific strength and specific rigidity,good damping performance,excellent machining performance,etc.Magnesium alloys also has good application prospect in the aerospace,transportation and other fields.Quasicrystal was first discovered by Shechtman and his colleagues in rapidly solidified Al-Mn alloy in 1984.Quasicrystal is a kind of solid ordered phase which has both long-range pseudo-periodicity and non crystallographic rotational symmetry,the special crystal structure of quasicrystal crystal materials make it has many excellent properties which the crystal materials don't have.The in-situ Mg-based quasicrystal phase provides a new path for the strengthening of magnesium alloys,which has become a hot spot of research.The conventional cast technology was used to prepare the alloys in this work,the in-situ quasicrystal reinforced Mg-Zn-Y-Zr alloy was prepared by adding different contents of Zn and Y elements,the effect of cooling rate,composition of the alloy and heat treatment on structure and properties of quasicrystal reinforced magnesium alloy were studied.The solidification path and formation mechanism of quasicrystals,and the strengthening mechanism of quasicrystal to alloy were researched.Through literature research,the initial alloy composition was set to Mg-3.6Zn-0.8Y-0.6Zr(wt.%),the effects of cooling rate on the microstructure and mechanical properties of the alloy was studied by using three different cooling methods.The influence of cooling rate on the phase formation of quasicrystal,and the solidification path of alloy under different cooling speed were analyzed.The results shown that under thedefinitized alloy composition,the cooling rate of Mg-3.6Zn-0.8Y-0.6Zr(wt.%)alloy has a decisive influence on the phase composition.The faster cooling rate is benefited to the formation of quasicrystal,and there is a huge difference on the structure and performance of the alloy under different cooling speed.The 4 groups of alloy gradients were designed under three different cooling processes.The effects of the alloy composition on the microstructure and performance of Mg-Zn-Y-Zr alloy with the same cooling rate were researched.The effect of alloy composition on the microstructure and properties of the alloy is summarized,the alloy was heat treated and the effect of heat treatment on the alloy was studied.A new cooling process is designed in this paper by combined with the influence of different cooling processes and alloy composition of Mg-Zn-Y-Zr alloy.The high performance quasicrystal reinforced Mg-5x%Zn-x%Y-0.6%Zr alloy has been prepared used the new cooling method.The Mg-6.5%Zn-1.3%Y-0.6%Zr alloy shows the most excellent mechanical properties,and the tensile strength and elongation of the cast state are 225 MPa and 25.2% respectively.