Effect Of Heat Treatment On The Microstructure And Properties Of Spray Formed 1420 Al-Li Alloy

1420 Al-Li alloy has high specific strength and stiffness,low density,high elastic modulus and good corrosion resistance,is currently one of the most widely used Al-Li alloy.The jet deposition method is used to prepare Al-Li alloy,which can effectively reduce the composition segregation in casting process,and refine the grain.At present,most of the research on 1420 Al-Li alloy is focused on the as-cast structure,and there are few researches on alloys prepared by spray deposition,this paper uses modern material analysis methods,SEM,OM,TEM,EBSD,XRD and mechanical property testing methods to study the changes in the microstructure,mechanical properties and tensile fracture modes of the spray-deposited 1420 Al-Li alloy under different heat treatment conditions.And reveal its internal connection,and design and optimize the heat treatment process of the alloy accordingly.The main results of the study are as follows:the main structure of the extrusion forming 1420 Al-Li alloy is composed of?-Al and?'(Al₃Li),S₁(Al₂Mg Li),?(Al Li)and?'(Al₃Zr).At the same time,the alloy grains are flat after hot extrusion It has obvious orientation and is distributed in a streamlined shape along the hot extrusion direction of the sheet.According to the results of DSC thermal analysis,the solution treatment was carried out at 450,460,470?.SEM and XRD results showed that the?',S₁,and?phases in the alloy were all dissolved.When the heating temperature was 515?and above,the alloy was overburned.After solution treatment at 450?×30min,the grain size is uniform,the average size is 2.91?m,the tensile strength of the alloy is 377MPa,the yield strength is 220MPa,and the elongation is 17.3%.The main precipitated phases in the alloy after aging treatment are?',S₁,?phase and?'/?'composite particles.The precipitation sequence is supersaturated solid solution??'phase??phase,and?'phase is the main aging at 120 and 140?at low temperature.Only?'phase precipitation and coarsening are involved within 48h of aging.No precipitation of?phase is detected.In the early stage of aging at 160 and180?,the?'phase is the main phase.When the aging conditions are 160?×48h and180?×18h,S1 and?phases begin to precipitate in the alloy.The change of the grain boundary precipitation-free zone(PFZ)is related to the types of alloy precipitated phases.The precipitated phases are mainly?'under low temperature aging and are dispersed in the crystal plane.The PFZ is narrow.S₁ phase precipitates near the grain boundary at the high temperature over-aging stage.,Increase the width of PFZ.After aging treatment at 120?,the alloy can maintain a higher strong plasticity;increasing the aging temperature,the strength of the alloy increases slightly,and the plasticity decreases greatly.After aging treatment at 120?×18h,the overall mechanical properties of the alloy are better,and the fracture mode is tough and brittle.For mixed fracture,the tensile strength is 473MPa,the yield strength is 301MPa,and the elongation is 15.9%.The electrical conductivity changes of the alloy after different aging treatment conditions are tested.The electrical conductivity of the alloy continues to increase with the increase of the aging time,and the growth rate is relatively fast at the initial stage of aging,and the rate gradually slows down with the increase of the aging time,and the conductivity tends to be balanced to a certain extent;The phase transition kinetic equations and conductivity equations under different aging conditions are established according to the changes in conductivity,and the parameter b values of the aging temperature of 120,140,160,and 180?are 0.097,0.213,0.343,and 0.752,respectively,and the parameter n values are respectively 0.813,0.687,0.613,0.435,and verify the significance of the equation.On this basis,the phase transition kinetic curve and isothermal transition kinetic curve(TTT)are drawn.