| Magnesium alloys,which are widely used in aviation,spaceflight,vehicle and electrommunication,have many outstanding properties,such as high specific strength,high specific stiffness,low density,good electromagnetic shielding performance and excellent damping capacity.At the same time,because of its poor plastic deformation ability, corrosion resistance,low yield stress and fracture toughness,the application and development of the wrought magnesium alloys are restricted remarkably.When RE(Ce-rich misch metal) and Sb are added together in the wrought magnesium alloys,the large needle-like rare earth phase disappears and the ball type phase comes forth.As a result,there are highly elevations in the integrated properties.However,the combination alloying of RE and Sb in the wrought magnesium alloys is not studied adequately.In addition,the effect of the alloying is not steady enough,which is the main obstacle to the extensive use of the addition of RE and Sb to the wrought magnesium alloys.In this paper,by means of optical microscopy(OM),x-ray diffractometry(XRD), scanning electron microscopy(SEM) equipped with an Energy Dispersive Spectrometer (EDS) system,the influences of the double addition of RE,Sb on the microstructure, mechanical property,corrosion resistance of the AZ31 magnesium alloy are systematically studied.At the same time,the law of good affection when RE,Sb are double added to the AZ31 is explored.Furthermore,the possibility of the double addition of RE and Sb to the AZ61 and AZ80 is studied and the precipitation process of the rare earth rich phases in the AZ31 which is combination alloyed of RE and Sb are studied by the method of kinetic control.While RE elements were added in the AZ31 suitably,the large needle-like rare earth phase Al11Ce3 generated and the shape of theβ-Mg17Al12 changed from Skeleton-like to oval-like and dot-like.After RE and Sb were double added to the AZ31 alloys,the granular RESb and Small spherical shaped Al-RE-Sb ternary rare-earth phase appeared.There was interaction between the microstructure of AZ31 alloys with RE and Sb and different the content of Al when the combination alloying of RE and Sb is used in the AZ31.While the content of Al was 3.2wt%,RE was 0.6～1.0%wt,and the content of Sb was 0.4～1.2%wt,the ratio of RE and Sb comed to 1:1;While the content of Al was 2.5%wt,the ratio of RE and Sb comed to 4:5;the good effect of alloying was showed.For instance,β- Mg17Al12 was fully broken up and the large needle-like rare earth phase basically had changed to granular and punctuate-like.The AZ31 alloy with content of Al about 3.2wt%which had good effect of the combination alloying of RE and Sb had more RESb and that with content of Al about 2.5wt%has relatively more Al-RE-Sb ternary rare-earth phase.The combination alloying of RE and Sb could enhance the mechanical properties of the AZ31 in varying degrees.When the content of Al was 3.2%wt,the addition of RE was 1%,the addition of Sb was 1%,it showd the respectively raising in the micro-hardness, tensile strength,yield strength and elongation compared to the AZ31 by 9%,31.4%,25.6% and 16.7%.when the content of Al was 2.5%wt,the addition of RE was 1%,the addition of Sb was 1.2%,it showed the respectively raising compared to the AZ31 by 9%,34.2%, 27.3%and 17.2%.The combination alloying of RE and Sb could improve the microstructure of the wrought magnesium alloys AZ61 and AZ80 with high content of Al.When 1%RE and 1%Sb were added to the AZ61 alloy,1.2%RE and 1.2%Sb were added to the AZ80 alloy, the large needle-like rare earth phase had changed to particle organization and theβ-Mg17Al12 had been broken up.Tensile strength and yield strength raised at least by 20% and the elongation raises by at least 10%.The combination alloying of RE and Sb could also raise the corrosion resistance of AZ series wrought magnesium alloys.For AZ31,when the content of Al was 3.2%wt,the addition of RE was 1%,the addition of Sb was 1%,the corrosion potential had increaseed 0.04v and the corrosion current density had reduced 3.22×10-5S A.cm-2.When the content of Al was 2.5%wt,the addition of RE was 1%,the addition of Sb was 1.2%,the corrosion potential had increased 0.045v and the corrosion current density had reduced 3.36×10-5 A.cm-2.For AZ61 and AZ80,the corrosion potential had increased 0.035v and 0.04v and the corrosion current density had reduced from 3.54×10-5 A.cm-2,2.31×10-5A.cm-2 to 7.86×10-6 A.cm-2 and 5.23×10-6 A.cm-2 respectively.By the means of thermodynamics analysis and dynamics control to simulate the precipitation process and growing of the rare-earth rich phase in the rare-earth alloyed AZ31 alloy,it could be come to the conclusion as below:For the needle-like rare earth phase's precipitation process,nucleation and its priority mission was a small needle-shaped beam radiation group gathered at the edge of the dendrites,with the growth of dendrites and the distribution of solute,it grow into an independent long needle-like phase and the mission bundle of small needle-like phase gradually dispersed.Eventually it grows into a large needle-like distributing along the grain boundary;For the spherical phase,the priority nucleation and precipitation of Sb-rich phase at the edge and with the redistribution of solute.Then Sb-rich phase continues to grow and the content of Al in part of Al-RE-Sb redistributes.These Al atoms generate Mg17Al12 with Mg atoms and some of them continue to grow into the Al-RE-Sb phase. |
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