| At present,magnesium-lithium（Mg-Li）alloys have broad potential application prospects in aerospace,automotive and electronics industries,but its widespread applications have been limited due to low strength and poor corrosion resistance.In this paper,the ultrasonic nanocrystal surface modification（UNSM）technology was used to modify the surface of Mg-Li alloy in order to further improve its mechanical properties and corrosion resistance.In this dissertation,four types of Mg-Li alloys LAE361,LA116,LA106,and LAE1081 were used as research objects.Based on the strengthening of alloying and hot rolling treatments,the effects of UNSM on the microstructure,deformation mechanism,mechanical properties and corrosion resistance of Mg-Li alloys were studied.The main research content includes:（1）The alloying method was used to study the mechanical properties and corrosion behavior of as-cast Mg-Li alloy.LAE361 Mg-Li alloy is a typical single phase Mg alloy withα-Mg.The other three alloys are dual-phase Mg alloys which composed ofα-Mg andβ-Li.Among the four alloys,LAE1081 Mg-Li alloy has the highest yield strength（151 MPa）,and LAE361 Mg-Li alloy has the highest tensile strength（186 MPa）.The LA106 Mg-Li alloy has good mechanical properties and corrosion resistance(the lowest corrosion current density:95.8μA cm-2)and the highest elongation（12.8%）.（2）The effects of hot rolling treatments on the texture,mechanical properties,and corrosion resistance of the Mg-Li alloy were studied.The composition of the Mg-Li alloy does not change,and theα-Mg phase mainly shows a typical basal texture after hot rolling.Theβ-Li phases of LA116,LA106,and LAE1081 Mg-Li alloys exhibitεandζfiber textures,γandηfiber textures,andα,ε,γfiber textures,respectively.The hardness of Mg-Li alloys increased after hot rolling,and LAE361 Mg-Li alloy was the most significant（increased by about 47.4%）.After hot rolling,LAE361 and LA116 Mg-Li alloys have improved strength and corrosion resistance,but poor plasticity.The mechanical properties of LA106 and LAE1081 Mg-Li alloys were improved,but the corrosion resistance were deteriorated.（3）Using orthogonal test method,the influence of UNSM process parameters on the hot-rolled LA106 Mg-Li alloy was studied.The effects of UNSM technology process parameters（static pressure,moving speed and feed）on the surface properties of hot-rolled LA106 Mg-Li alloy（hardness,roughness,and depth of hardening layer）were studied.The results show that the order of influence of UNSM process parameters on the comprehensive strengthening effect of LA106 Mg-Li alloy is:static pressure,feed,and moving speed.After multi-objective optimization design,the best combination of UNSM process parameters:static pressure is 0.3 MPa,moving speed is 1500 mm/min,and feed is 0.05 mm.（4）Using UNSM technology to perform surface strengthening treatment on the hot-rolled Mg-Li alloy,and the microstructure evolution,deformation mechanisms,mechanical properties,and corrosion resistance of Mg-Li alloys were investigated.LAE361 and LA106 Mg-Li alloys obtained severe plastic deformation layers on the surface and the surface grains were refined after UNSM treatments.At the same time,the basal texture intensity of Mg-Li alloys is significantly reduced,and a large amount of deformation twins appear on the surface layer,soα-Mg phase of the surface layer undergoes twin deformation and the basal slip.And for the LA106 Mg-Li alloy,theβ-Li phase changes fromγandηfiber texture toαandεfiber texture,which mainly occurs dislocation slip.After UNSM treatments,the surface hardness of LAE361 and LA106 Mg-Li alloys increased by 17.5%and 39%respectively,and depth of hardening layer reached 350μm.Mg-Li alloys have increased strength and improved plasticity.After UNSM treatments,the corrosion current density of the LAE361 Mg-Li alloy decreased by about 29.3%,and the corrosion resistance was significantly improved.While the corrosion current density of the LA106 Mg-Li alloy increased by 189.7%,and the corrosion resistance deteriorated. |
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