Basic Research About Controlling Of Microstructure And Mechanical Properties Of Mg-6Gd-3Y-0.6Zr-Sn/Zn Magnesium Alloys

Mg-Gd-Y-Zr based magnesium alloys are thought as a potential high strength alloys and have very wide applications in automotive,aerospace and other industries.However,the industrial application of the current Mg-Gd-Y-Zr based high strength magnesium alloys is limited due to some existing problems such as high cost.Therefore,it is very necessary to research and develop Mg-Gd-Y-Zr based high strength magnesium alloys with relatively low cost.It is well known that alloying and/or micro-alloying which are thought as an important method to research and develop magnesium alloys,has successfully used to develop magnesium alloys with high-performance.At present,among the various alloying and/or micro-alloying elements for the modification of magnesium alloys,Sn and Zn have received much attention due to their high precipitation strengthening effects,low cost and so on.However,up to now,the investigations about the modification of Mg-Gd-Y-Zr based alloys by using Sn and Zn especially Sn are very rare.Therefore,the basic research about the controlling of the microstructure and mechanical properties for Mg-Gd-Y-Zr-Sn/Zn based magnesium alloys,has very important theoretical significance and practicable value in developing high strength Mg-Gd-Y-Zr based magnesium alloys with relatively low cost and widening their application.Based on the Mg-6Gd-3Y-0.6Zr and Mg-6Gd-3Y-0.6Zr-Sn/Zn(wt.%)based experimental magnesium alloys designed in this paper,both the effects of Sn and Zn additions especially Sn and their adding amount on the microstructure and mechanical properties of the Mg-6Gd-3Y-0.6Zr based experimental alloys and the effects of heat treatment on the microstructure and mechanical properties of the Mg-6Gd-3Y-0.6Zr-Sn/Zn experimental alloy,were investigated by using optical microstructure(OM),X-Ray diffraction(XRD),scanning electron microstructure(SEM)and energy disperse spectroscopy(EDS),differential scanning calorimeter(DSC),micro-hardness and tensile properties testing,and the following main research results were obtained:1)The as-cast microstructure of the Mg-6Gd-3Y-0.6Zr experimental magnesium alloy is mainly composed of ?-Mg,isolated island-like Mg5 Gd phase and regular small block-like Mg24Y5 phase,and the as-cast tensile and yield strengthes,elongation at room temperature(RT)for the alloy respectively reach 190 Mpa,136Mpa and 4.7%.2)Adding 1-3 wt.%Sn to the Mg-6Gd-3Y-0.6Zr experimental magnesium alloy has a certain degree of effect on the as-cast microstructure of the alloy.After 1wt.% Sn additionto the alloy,the amount of Mg5 Gd and Mg24Y5 phases decreases and the particle-like Sn3Y5 new phases are formed.At the same time,2 wt.% Sn addition to the alloy causes the amount of Mg5 Gd and Mg24Y5 phases to further decrease and the morphology of the Sn3Y5 phase changes to the needle-like shape.Furthermore,after 3wt.% Sn addition to the alloy,the Mg5 Gd and Mg24Y5 phases are barely detected in the alloy and the formed main Sn-containing phases are irregular block-like MgSnY.In addition,1-3 wt.%Sn additions to the Mg-6Gd-3Y-0.6Zr alloy cause the as-cast tensile properties at RT to decrease,indicating that under the experimental conditions in this paper Sn addition is not beneficial to the as-cast tensile properties at RT for the alloy.Among the alloys with 1-3 wt.%Sn additions,the alloy with 1 wt.%Sn addition exhibits the relatively high as-cast tensile properties at RT.3)After treated by T4(500?×12h+water quenching)for the Mg-6Gd-3Y-0.6Zr experimental magnesium alloy,the Mg5 Gd and Mg24Y5 phases in the alloy almost have dissolved into the matrix.Although the tensile properties at RT for the T4-treated Mg-6Gd-3Y-0.6Zr alloy are relatively poorer than those for the corresponding as-cast alloy,the T6(500?×12h+water quenching +200?×96h+air cooling)treatment is beneficial to the tensile properties of the Mg-6Gd-3Y-0.6Zr alloy.The tensile and yield strengthes,elongation at RT for the T6-treated alloy respectively reach 268 Mpa,206Mpa and 4.3%.4)After treated by T4(500?×12h+water quenching)for the Mg-6Gd-3Y-0.6Zr experimental magnesium alloys with 1-3 wt.%Sn additions,the Mg5 Gd and Mg24Y5 phases in the alloys also have basically dissolved into the matrix,however,the Sn3Y5 phase and MgSnY phases in the alloys are still obviously observed.In addition,Sn addition also is not beneficial to the tensile properties of the T4-and T6-treated Mg-6Gd-3Y-0.6Zr alloys(T4: 500?×12h + water quenching;T6: 500?×12h + water quenching + 200?×96h + air cooling).Among the Sn-containing Mg-6Gd-3Y-0.6Zr alloys,the T4-and T6-treated alloys with 1 wt.%Sn addition exhibit relatively higher tensile properties at RT than other alloys.5)Zn addition to the Mg-6Gd-3Y-0.6Zr experimental magnesium alloy has an obvious effect on the as-cast microstructure of the alloy.After 2 wt.% Zn addition to the alloy,the Mg5 Gd and Mg24Y5 phases are barely detected in the alloy and a great amount of the Mg12 YZn phases with the semi-continuous nets and/or lamellar shapes are formed along grain boundaries.In addition,different to 1-3 wt.%Sn additions,both 2 wt.%Zn and1 wt.%Sn+1 wt.%Zn additions to the Mg-6Gd-3Y-0.6Zr alloy are beneficial to the as-cast tensile properties at RT.However,after respectively treated by T4(500?×12h+water quenching)and T6(500?×12h+water quenching +200?×96h+air cooling)for the alloyswith 2 wt.%Zn and 1 wt.%Sn+1 wt.%Zn additions,the change in the tensile properties at RT for the two alloys is different.The tensile properties at RT for the T4-and T6-treated alloys with 2 wt.%Zn addition are relatively poorer than those for the corresponding as-cast alloy,respectively.Oppositely,The tensile properties at RT for the T4-and T6-treated alloys with 1 wt.%Sn+1 wt.%Zn additions are relatively higher than those for the corresponding as-cast alloy,respectively.