Microstructure And Properties Of 2195 Al-Li Alloy Prepared By Spray Forming Technology

Al-Li alloy has become the most potential novel metal structure material in aerospace and military fields because of its low density,high strength,good fracture toughness and fatigue crack growth resistance.At present,there are mainly three preparation technologies to produce Al-Li alloys:traditional casting,powder metallurgy and spray forming.Spray forming process with its rapid solidification characteristics solves the problem of macro/micro segregation and coarse grain in traditional casting process,and avoid oxide contamination in powder metallurgy process effectively,so spray forming has a good prospect in the production of Al-Li alloy.In this work,the spray formed 2195 Al-Li alloy were investigated by X-ray diffraction,3D X-ray microscopy,scanning electron microscopy,transmission electron microscopy,electron backscatter diffraction,electron probe microanalyser,energy dispersive spectroscopy,hardness testing and tensile testing.The following cases were systematically studied:(1)microstructure and mechanical properties of Al-Li alloys prepared by traditional casting and spray forming;(2)analysis of grain coarsening on the surface of 2195 extruded plate;(3)effect of natural aging and pre-deformation on the properties of 2195 extruded bar.The main conclusions are as follows:(1)The as-sprayed alloy consists fine equiaxed grains with abundant pores,semi-continuous/discontinuous secondary phases(Al-Cu phase and Al-Cu-Fe phase)in grain boundary,and coarse T₁(Al₂Cu Li)and T_B(Al_7.5Cu₄Li)phases distributed uniformly in grain interior.While as-cast alloy contains coarse grains with obvious dendrite and small amount of pores,continuous secondary phases(Al-Cu-Mg phase,Al-Cu phase and Al-Cu-Fe phase)in grain boundary,and fine T₁,T_Band?(Al₅Cu₆Mg₂)phases distributed in grain interior close to the grain boundary.The same homogenization treatment shows more solute contents dissolved in the spray formed2195 alloy.The as-sprayed alloy has advantage of 35%in ultimate strength,26%in yield strength and 54%in elongation compared to the as-cast alloy,respectively.(2)The main reasons for the coarsening of surface grains in extruded plate during the process of solution treatment are as follows.Firstly,the coarse secondary phase with small amount and large-scale Zr-containing phases exist on the surface of the plate,which weakens the inhibition of grain growth.Then,higher storage energy presents in the surface of extruded plate due to the larger strain during rolling,indicating the dominance of recrystallization through solution treatment.Therefore,the grain coarsening is obvious on the surface.(3)During natural aging to 360 h,the tensile strength,yield strength and elongation of the spray formed alloy increased 41.5%,86.2%and 14.3%,respectively.In addition,natural aging may prolong the time reaching peak aging during artificial aging,while it can improve the strength of peak aging.Natural aging and pre-deformation before artificial aging can improve the peak hardness of the alloy,and the hardness of the alloy can maintain a high level under long-term aging.