Effects Of Alloying On The Microstructure And Mechanical Properties Of Wrought AZ61Alloys

The RE element(Sm), Ca and Sb were added to AZ61magesium alloy. Theexperimental alloys AZ61-0.5Ca-xSm (x=0,0.6,1.0,1.5) and AZ61-1Sm-xSb(x=0,0.5,1.0,1.5) were prepared in an induction fuenace under the Ar atmosphere. Thosealloys were homogenized at420℃for10h, and then extruded at360℃with anextrusion ratio of25and an extrusion speed of about2.5m/min. Additionally, Differentheat treatments were used on those as-extruded alloys, such as solid solution treatment,artificial aging treatment and aolution and aging treatment. The actual chenmicalcontents of as-cast alloys were analyzed by X-ray fluorescence spectrometer (XRF) andatomic emission spectrometer (ICP). All the microstructures were studied by X-raydifferaction (XRD), optical microscopy (OM), scanning electron microscopy (SEM),energy-dispersive X-ray spectrometer (EDS) and transmission electron (TEM). Thehardness and tensile properties were tested by micro-hardness and tensile test,respectively. The results indicate that:①The major compound in AZ61is β-Mg17Al12, while the major compounds inAZ61-1Sm alloy are β-Mg17Al12, Al2Sm and Al3Sm. While adding some Sb inAZ61-1Sm alloy, the new compound SbSm was formed. However, the volume of SbSmcompound increases with the increase of Sb content. The major compounds inAZ61-0.5Ca alloy are β-Mg17Al12and Al4Ca which looks like skeletons. There is nonew compound formed after Sm added in AZ61-0.5Ca alloy, except the Al2Sm andAl3Sm.②Addition of1.0wt%Sm and0.5wt%Ca make the shape of β-Mg17Al12transform from continous network to discontinuous network. In AZ61-1Sm alloy withadding of Sb element, increasing the content of Sb, the discontious network β-Mg17Al12phases become granular β-Mg17Al12gradually. In AZ61-1Sm-1.5Sb alloy, there existdispersed granular β-Mg17Al12, Al2Sm and Al3Sm. However, some bulk SbSm phaseswith large volume are formed in that alloy as well. In AZ61-0.5Ca alloy with addition ofSm, the content of granular phase will increase significantly and the distribution will bediffuse when the content of Sm increased.③Addition of Sm and Sbenhanced the strength of hot-extruded AZ61alloys atroom temperature slightly and enhanced the strength at150℃obviously. In addition,there is a further advance of mechanical properties at elevated temperature while adding some Sb into hot-extruded AZ61-1Sm alloy. Yield strength of hot-extruded AZ61-0.5Cais higher than hot-extruded AZ61. What’s more, addition of Sm could increase thetensile strength and yield strength both at room temperature and150℃, significantly.④After the solid solution treatment(T4), all the β-Mg17Al12compoundsdistributing at grain boundaries in hot-extruded AZ61-1Sm-xSb and AZ61-0.5Ca-xSmare dissolved into matrix. The solution treatment temperature and heat preservation timeare400℃and8hours respectively. After aging treatmentprocess (T5), there are somelamellar shape β-Mg17Al12compounds and granular shape β-Mg17Al12compoundsprecipitate in the hot-extruded alloys and hot-extruded-T4alloys. The aging treatmenttemperature and heat preservation time are180℃and48hours respectively.In addition,the lamellar shape β-Mg17Al12compounds distribut in the grains while the granularshape β-Mg17Al12compounds distribute along the grain boundries.⑤To AZ61-1Sm-xSb and AZ61-0.5Ca-xSm alloys, the tensile strength and yieldstrength of hot-extruded alloys are lower than T5-treated alloys, but higher thanT4-treated alloys. However, the tensile properties of solution&aging treated alloys arehigher than hot-extruded alloys, but lower than T5-treated alloys.