Basic Research About Controlling Of Microstructure And Mechanical Properties For Sm-containing Magnesium Alloys

Sm-containing based magnesium alloys are thought as a potential alloys and their research has received much global attention.At present,the research about Sm-containing based magnesium alloys mainly focus on the establishment of their phase diagrams,the modification of present magnesium alloys by using Sm alloying and/or micro-alloying,and so on.The development of the new Sm-containing based magnesium alloys in which Sm is designed as a main element,is very limited.In addition,the investigations about the effects of Sm alloying and/or micro-alloying on the microstructure and mechanical properties of present magnesium alloys also are not very systematical.First,the related magnesium alloys specifications are very rare;Secondly,the research about the effects of the alloying and/or micro-alloying of other elements on the microstructure and mechanical properties of Sm-containing magnesium alloys are not basically carried out.Therefore,the basic research about the controlling of the microstructure and mechanical properties for Sm-containing magnesium alloys has very important theoretical significance and practicable value in developing Sm-containing based magnesium alloys with high properties and widening the application of magnesium alloys.Based on the Mg-3Sm-1.2Mn-0.9Sc/1Zn and Mg-3Y-2Zn-0.6Zr(wt.%)based magnesium alloys designed in this paper,both the effects of Zr micro-alloying and heat treatment on the microstructure and mechanical properties of the Mg-3Sm-1.2Mn-0.9Sc/1Zn based experimental alloys and the effects of Sm addition and heat treatment on the microstructure and mechanical properties of the Mg-3Y-2Zn-0.6Zr experimental alloy,were investigated by using differential scanning calorimetry(DSC),optical microscope(OM),X-Ray diffraction(XRD),scanning electron microscope(SEM)and properties testing,and the following main research results were obtained:(1)The as-cast microstructure of the Mg-3Sm-1.2Mn-0.9Sc experimental magnesium alloy mainly contains ?-Mg,Mn2 Sc and particle-like Mg41Sm5 phase with small amount.At the same time,after 0.6wt.%Zr addition to the Mg-3Sm-1.2Mn-0.9Sc alloy,the change in the type of alloying phases in the as-cast microstructure of the alloy is not obvious but the grains are refined.In addition,0.6wt.%Zr addition to the Mg-3Sm-1.2Mn-0.9Sc alloy causes different degrees of decrese in the as-cast tensile properties at room temperature(RT).(2)Heat treatment has great influence on the tensile properties at RT for the Mg-3Sm-1.2Mn-0.9Sc based experimental magnesium alloys.After treated by T4(525?× 12h+water quenching)and T6(525 ? × 12h+water quenching+250 ? × 24h+air cooling),the tensile strength and elongation of the Mg-3Sm-1.2Mn-0.9Sc alloys with and without Zr addition respectively increase but the yield strengths for the two alloys relatively decrease.The improvement in the tensile properties at RT for the T6-treated alloys is relatively more obvious than that for the T4-treated alloys.In addition,after treated by T5(275?×36h/48h)for the Mg-3Sm-1.2Mn-0.9Sc based alloys,the tensile properties at RT for the alloy without Zr addition decrease,and an increase in the T5-treated time causes the tensile strength and elongation to further decrease.Oppositely,the tensile properties at RT for the T5-treated alloy with Zr addition relatively increase,and an increase in the T5-treated time causes the tensile strength and elongation to further increase.(3)The as-cast microstructure of the Mg-3Sm-1.2Mn-1Zn experimental magnesium alloy is mainly composed of the ?-Mg and Mg41Sm5 phases.At the same time,after 0.6 wt.%Zr addition to the Mg-3Sm-1.2Mn-1Zn alloy,the change in the type of alloying phases in the as-cast microstructure of the alloy is not obvious but the grains are obviouly refined.In addition,0.6 wt.%Zr addition to the Mg-3Sm-1.2Mn-1Zn alloy causes an obvious increase in the as-cast tensile properties at RT.(4)The effect of heat treatment on the tensile properties at RT for Mg-3Sm-1.2Mn-1Zn based experimental magnesium alloys is very obvious.After treated by T4(500?×12h+water quenching),the improvement in the tensile properties at RT for alloy without Zr addition is very obvious.As for the alloy with Zr addition,T4 treatment also can obviously improve the tensile strength and elongation at RT for the alloy but the yield strength at RT for its T4-treated alloy slightly decreases.At the same time,the improvement in the tensile properties at RT for the T6(500 ? × 12h+water quenching+250?×24h+air cooling)-treated Mg-3Sm-1.2Mn-1Zn alloys with and without Zr addition is not obvious as compared with that for the corresponding T4-treated alloys.In addition,after treated by T5(275?×36h/48h)for the Mg-3Sm-1.2Mn-1Zn based alloys,the tensile properties at RT for the alloy with Zr addition decrease,oppositely,the tensile properties at RT for the alloy without Zr addition slightly increase.(5)The as-cast microstructure of Mg-3Y-2Zn-0.6Zr experimental magnesium alloy mainly contains ?-Mg,Mg12YZn(X),Mg3Y2Zn3(W)and a small number of Mg24Y5 phases.After adding 3wt.%Sm to the Mg-3Y-2Zn-0.6Zr alloy,the type of alloying phases in the as-cast microstructure of the alloy does not change.At the same time,3 wt.% Sm addition to the Mg-3Y-2Zn-0.6Zr alloy causes the tensile properties at RT to decrease.Furthermore,the effects of heat treatment on the tensile properties at RT for the Mg-3Y-2Zn-0.6Zr alloys with and without Sm addition are different.After treated by T4(500?×24h+water quenching),the tensile and yield strengthes,elongation at RT for the alloy without Sm addition decrease.As for the alloy with Sm addition,although T4 treatment causes the elongation at RT for the alloy to greatly increase,its the tensile and yield strengthes simultaneously decrease.In addition,after treated by T6(500 ? × 24h+water quenching+225?×12h+air cooling)for the alloys with and without Sm addition,their tensile strength especially elongation obviously increase in spite of a slight decrease in the yield strength.