Preparation And Study On Microstructure And Properties Of Mg-Li-Y-Zn Alloys

As the lightest metal structure material to date,Mg-Li alloy has been widely concerned by researchers in many fields such as national defense science and technology,aerospace,automobile,electrical appliances and communications,sports equipment and so on in the era of energy saving and emission reduction and the pursuit of light quantification.However,the absolute strength of Mg-Li alloy is relatively low,and its creep resistance and corrosion resistance are also very poor at present,which greatly restricts the application of Mg-Li alloy.It has reported that adding Y into magnesium alloy can not only improve the mechanical properties at room temperature,but also form the second phase with high melting point,which can improve the thermal stability of the alloy.And in recent years,the LPSO phase found in Mg-Y-Zn alloy has been more and more concerned because of its significant improvement on the mechanical properties,high temperature resistance and corrosion resistance of the alloy.In this paper,a dual phase Mg-Li alloy was prepared by mixing and fusing method and the extrusion deformation of the alloy was made to prepare the extruded test alloys.The microstructure of the test alloys is characterized and analyzed by means of optical microscopy?OM?,scanning electron microscopy?SEM?,energy dispersive spectrometer?EDS?and X ray diffractometer?XRD?.The effects of the addition of Zn and Y elements on the microstructure and mechanical properties of Mg-6.5Li-xY-yZn alloy were studied.The influence of extrusion deformation on the microstructure and properties of the alloy was discussed.Finally,the corrosion behavior of the as-extruded test alloy was systematically studied and analyzed.The main results are as follows:?1?The microstructure of the cast Mg-6.5Li-xY-yZn test alloy is mainly composed of the phase of?-Mg and?-Li,and the second phase in the grain boundary of?-Mg and the phase of?-Mg/?-Li.The addition of Zn and Y elements has obvious spheroidizing effect on the?-Mg phase.?2?After SEM energy spectrum and XRD phase analysis,the second phase of Mg-6.5Li-0.8Y alloys is mainly Mg₂Y phase.The second phase of Mg-6.5Li-0.8Y-0.3Zn alloys is finely striped,which is X-Mg₁₂ZnY?LPSO?.The granular dispersed phase in Mg-6.5Li-1.0Y-1.0Zn alloy is mainly W-Mg₃Zn₃Y₂ phase.?3?Compared with the as-cast alloys,the microstructure of the extruded alloy is obviously refined.In the direction of extrusion,both the?-Mg phase and the?-Li phase are elongated,and the second phase in the experimental alloy is also broken in the interface of the?-Mg/?-Li phase.The tensile test results at room temperature indicate that the comprehensive mechanical properties of the as-extruded alloys are greatly improved compared with the as-cast ones.?4?The corrosion behavior of extruded Mg-6.5Li-xY-yZn alloys was determined by means of corrosion weight loss method and hydrogen evolution gas collection test.The results show that the corrosion weight loss rate of Mg-6.5Li-0.8Y-0.3Zn alloy with LPSO phase is the lowest and the rate of hydrogen evolution is also the smallest.In the electrochemical performance test,we can get the polarization curves of the three groups of test alloys.The results show that the self-corrosion potential of Mg-6.5Li-0.8Y-0.3Zn alloy is the highest and the corrosion current is also the smallest,showing a good corrosion resistance.?5?The surface corrosion state of extruded alloy in 3.5wt.%NaCl solution soaked for 48h was analyzed by means of SEM.The results show that Mg-6.5Li-0.8Y-0.3Zn alloy with best corrosion resistance has the best surface state,which is characterized by pitting corrosion.A large number of deep and uniform corrosion pits were found on the surface of Mg-6.5Li-0.8Y alloy with the worst corrosion resistance.The surface of Mg-6.5Li-1.0Y-1.0Zn alloy is characterized by local corrosion.