Effect Of Thermo-Mechanical Treatment On The Microstructure And Mechanical Properties Of Al-2.4Cu-0.9Li-0.7Mg Alloy

Al-Cu-Li-Mg alloy is an age-strengthening alloy with low density,high modulus of elasticity,high specific strength and good corrosion resistance,thus it is widely used in aerospace field.The mechanical properties of Al-Cu-Li-Mg alloy is closely related to nano precipitates formed during heat treatment process.Many researches are focus on the influence of small pre-deformation thermo-mechanical treatment on the mechanical properties and microstructure of Al-Cu-Li-Mg alloy,however,the influence of large pre-deformation and introducing pre-aging before large-deformation thermo-mechanical treatment on Al-Cu-Li-Mg alloy is less researched.In this paper,the effects of introducing large pre-deformation and pre-aging to thermo-mechanical treatment on the microstructure and mechanical properties of Al-2.4Cu-0.9Li-0.7Mg alloy were systematically studied by hardness test,tensile test,EBSD test and TEM characterization.The relationship between microstructure and mechanical properties of the alloy was analyzed.The main conclusions are drawn as followed:?1?In the early stage of 150?¹80? aging,there are many different types of GPB zones composited together in the matrix,which mainly consist of GPBII zones with Li-contained GPB zones on its shell domain.As the aging time extends,the number density of the composite phases will decrease,while the number of Li-contained GPB zones will increase significantly.?2?when aging at 150?¹80?,the main precipitates are GPB zones,in which Li-contained GPB zones and its composite phase constitute the majority.Besides,there are also a small number of lath-like S phases which distribute in the shape of dislocation and a few of large T₁ phases.Compared with aging at 150? and 180?,on the peak aging condition of 200?,the number of S phases increased and the size are larger,while the number of Li-contained GPB zones decreased.?3?At the same aging temperature,as the amount of pre-deformation increases,the aging response rate accelerates,and the time to peak aging shortens.In addition,the strength of the alloy firstly increases and then decreased.The alloy with 50%pre-deformation gets the highest hardness and strength,the elongation firstly decreased and then stabilized.?4?Compared with T6 treatment,pre-deformation in thermo-mechanical treatment introduces dislocations to the alloy,which significantly changes the subsequent precipitation behavior,leads to the disappearance of the GPB zones which is easily formed in T6 treatment and the increasement of S phase and T₁ phase with smaller size.?5?Introducing pre-aging before pre-deformation induces a great number of dispersed GPB zones precipitate in the matrix,which greatly decrease the inhomogeneity of dislocation pile-up.Therefore,the size of S phase and T₁ phase precipitated during the subsequent aging process becomes smaller and the number of S phase and T₁ phase becomes larger and distribute more uniformly,eventually results in the alloy to have a optimal combination of strength and ductility.