| Magnesium alloys which are thought as the lightest engineering structuralmaterials, have great potential for the applications in automotive, aerospace and otherareas. However, the mechanical properties at high temperatures for the availablemagnesium alloys do not meet the needs of industrial production. Therefore, it is verynecessary to further develop new magnesium alloys with high performance. SinceMg-Al-Sr based magnesium alloys are thought as a potential heat-resistant alloys withlow cost, their research has received much global attention. But up to now, theresearch about Mg-Al-Sr based magnesium alloys mainly focus on these alloys withrelatively low aluminium content (≤6wt%), the invstigations about the Mg-Al-Srbased magnesium alloys with relatively high aluminium content (≥10wt%) are verylimited. Therefore, the basic research about the controlling of the microstructure andmechanical properties for the Mg-Al-Sr based magnesium alloys with relatively highaluminium content, which is predicted to have very important theoretical significanceand practicable value in developing and promoting the application for the Mg-Al-Srbased magnesium alloys with high performance.Based on the designed Mg-12Al-2Sr-0.3Mn (wt.%) magnesium alloy andcombined with using optical microscope (OM), scanning electron microscope (SEM),X-Ray diffraction (XRD), differential scanning calorimetry (DSC) and tensileproperties testing, the effects of minor Ca and Ti additions, and heat treatment on themicrostructure and tensile properties at room temperature (RT) for theMg-12Al-2Sr-0.3Mn (wt.%) alloy, were investigated, and the following main resultswere obtained in the paper:1）The as-cast Mg-12Al-2Sr-0.3Mn experimental alloy is mainly composed of-Mg, Mg17Al12and Al4Sr phases. Adding0.1-0.3wt%Ti to the Mg-12Al-2Sr-0.3Mnalloy do not cause the formation of any new phases in the alloy but can refine thegrains of the alloy, and an increase in Ti content from0.1wt%to0.3wt%causes therefining efficiency to gradually increase.2）The additions of0.1-0.3wt%Ti to the Mg-12Al-2Sr-0.3Mn experimental alloyhave certain influence on the tensile properties at RT for the alloy, and an increase inTi content from0.1wt%to0.3wt%causes the as-cast tensile and yield strengthes ofthe Ti-containing alloys to gradually increase but results in their as-cast elongation to gradually decrease. At the same time, after being treated by T6(420℃×24h+watercooling+250℃×32-48h+air cooling), the tensile and yield strengthes of the alloyswith and without Ti addition are improved but their elongations are slightly decreased.Furthermore, for a given aged temperature of250℃, with the aged time increasingfrom16h to32h, the tensile and yield strengthes of the experimental alloys graduallyincrease but the change in the elongations for the experimental alloys is not obvious.However, further increase in the aged time from32h to48h does not cause thetensile strength, yield strength and the elongation at RT for the experimental alloys toobviously change.3）The addition of0.3wt%Ca to the Mg-12Al-2Sr-0.3Mn experimental alloy doesnot cause the formation of any new phases in the alloy but can refine the grains of thealloy. Accordingly, the as-cast tensile and yield strengthes of tha Ca-containing alloyare slightly improved. Meanwhile, after being treated by T6(420℃×24h+watercooling+250℃×32-48h+air cooling), the tensile and yield strengthes of theCa-containing alloy are obviously improved but its elongation is slightly decreased. Inaddition, for a given aged temperature of250℃, with the aged time increasing from16h to32h, the tensile and yield strengthes of the Ca-containing alloy obviouslyincrease but its elongations is slightly decreased. However, further increase in theaged time from32h to48h does not cause the elongation at RT for the Ca-containingalloy to obviously change but results in its tensile and yield strengthes to decrease.4）Adding0.2wt%Ti+0.3wt%Ca to the Mg-12Al-2Sr-0.3Mn experimental alloyhas no obvious influence on the type of the secondary phases in the alloy but canslightly refines the grains of the alloy. As compared with the additions of0.3wt%Caand0.2wt%Ti to the Mg-12Al-2Sr-0.3Mn alloy, the refining efficiency of0.2wt%Ti+0.3wt%Ca addition to the alloy is relatively poorer.5) Adding0.2wt%Ti+0.3wt%Ca to the Mg-12Al-2Sr-0.3Mn experimental alloycan slightly improve the as-cast tensile and yield strengthes but has not obviouseffect on the on the elongation. As compared with the additions of0.3wt%Ca and0.2wt%Ti to the Mg-12Al-2Sr-0.3Mn alloy, the improvement in the the tensile andyield strengthes at RT for0.2wt%Ti+0.3wt%Ca addition to the alloy is relativelypoorer. At the same time, after being treated by T6(420℃×24h+water cooling+250℃×32-48h+air cooling), the tensile and yield strengthes at RT for the alloy with Tiand Ca additions are improved but its elongation is slightly decreased. Furthermore,for a given aged temperature of250℃, with the aged time increasing from16h to32 h, the tensile and yield strengthes of the alloy with Ti and Ca additions are obviouslyincreased but its elongation exhibits a decreasing tendency. However, further increasein the aged time from32h to48h does not cause the yield strength and elongation atRT for the alloy with Ti and Ca additions to obviously change but results in its tensilestrength at RT to decrease. |
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