Preparation And Research On Microstructure And Properties Of New Ultralight Mg-Li-Al-Gd Alloys

With the increasing consumption of metal mineral resources and worseenvironment pollution, abundant magnesium resources in china are paid more attentionamong public because of the great need of the weight-light structure materials inmanufacturing industry. Mg-Li alloy becomes the hot topic among every country.Mg-Li alloys, the lightest alloy materials, are possessed of several advantages includinghigh specific strength, good thermal conductance, good damping vibration, excellentelectromagnetic shielding performance and recyclability, which are used widely inmany fields such as automobile, military, aerospace, communication, electronicsindustries. However, the application of Mg-Li alloys is limited because of the poorcorrosion resistance, low strength and thermostability.Al, as the most important alloying element, is beneficial to the tensile strength aswell as the casting abilities. Li serves as the first alloying element to the super lightmagnesium alloy.in this study, Mg-9Li-3Al-xGd are made which are based on theduplex-phase Mg-Li-Al alloy. The influence of Gd on the microstructure, mechanicalproperties and corrosion resistance of as-cast and as-extruded Mg-9Li-3Al alloysthrough the processes of extrusion and solid-solution are investigated by opticalmicroscopy(OM), scanning electronic microscopy (SEM), X-ray diffraction (XRD)mechanical properties testing and electrochemical workstation. The results reveal asfollow:①The addition of Gd can effectively refine the microstructure of the alloys. Withthe content of Gd increasing, microstructure of the alloys are firstly coarsecotton-shaped and then flake-shaped, finally, small trip and needle-shaped, at the sametime, the amount of α-Mg decreases. However, the grain size increases to some degreewhen the content of Gd changes from2.0wt%to2.5wt%.②Mg-9Li-3Al alloy is composed of α-Mg、β-Li,small amount of Mg17Al12andMgLi2Al. The Mg17Al12distributed the boundaries of α-Mg is replaced by the AL3Gdafter Gd is added to the alloy. With the content of Gd increasing, the amount ofMg17Al12decreases finally can’t be found.③The mechanical properties of as-cast Mg-9Li-3Al-xGd alloys indicate that: Theaddition of Gd can clearly improve the tensile strength and yield strength. The tensile strength and yield strength firstly increase and then decrease with the content of Gdincreasing. When the content of Gd is2.0%the tensile strength and yield strength reachto the max values,180MPa and174MPa, respectively, which are enhanced by51.3%and83.2%compared with that of the alloy without the addition of Gd. Elongationof the alloys increase a little with the content of Gd increasing. When the content of Gdis2.5%, the highest elongation is15.7%, which is enhanced by19.8%compared withthat of the alloy without the addition of Gd.④After extrusion, big bulk α-Mg is broken up, the dynamic recrystallizationoccurs during extrusion, which has positive effect on the refinement of themicrostructure. The tensile strength and plastic are obviously improved.⑤The corrosion resistance of as-extruded Mg-9Li-3Al-xGd first increase, thendecrease and finally increase with the content of Gd increasing. The corrosion resistanceincreases when the content of Gd is more than1.5%.⑥Solid solution treatment can improve the conductivity of the alloys withoutreduce the strength significantly.