Effect Of Trace Ce, Zr, Zn Elements And Pre-deformation On Microstructures And Properties Of Al-Li-Cu-Mg-Ag Alloy

Owing to advantages of low density, high strength and perfect corrosion resistance, Al-Li Alloy is gradually substituting for traditional Al alloys and becoming an ideal structural material of aerospace. Hence, it is becoming an important topic for present aerospace materials to research and develop the Al-Li alloys with excellent performance. The effects of trace Ce, Zr, Zn and different predeformation on mechanical properties and microstructures of Al-Li alloy in this paper had been analyzed by adopting room temperature mechanical property tests, metallographic microstructure observation, electrical conductivity tests, differential scanning calorimetric (DSC), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy diffraction X-ray spectrum (EDXS) and transmission electron microscopy (TEM) observation. The obtained experimental results were as following.1、After artificial aged at T6(180℃), sequence of mechanical properties of three kinds of A, B and C alloy containing trace Ce, Ce+Zr and Ce+Zr+Zn elements separately was the best for C alloy, the second for B alloy and the worst for A alloy. The values of strength and plasticity of alloys were given: σ0.2=632.8MPa,δ=6.4%for C(Ce+Zr+Zn) alloy, σ0.2=530.9MPa,δ=6.4%for B(Ce+Zr) alloy and σ0.2=480.7MPa,δ=8.8%for A(Ce) alloy.2、The effect of adding trace Ce+Zr+Zn elements simultaneously on refinement of alloy re-crystallization grains was better than those of Ce+Zr and Ce contained alloys. The role of improving fracture mode of alloys was: Ce+Zr+Zn>Ce+Zr>Ce. The fracture modes of alloys gradually transferred from the brittle intergranular crack mode of A(Ce contained) alloy to the based on dimples toughness transgranular crack mode.3、There was little change on the mainly strengthening precipitates of alloys by adding Ce, Zr and Zn elements. The mainly strengthening phases of A, B and C alloys were still T1,θ’, and a small amount of cubic phase (σ:Al5Cu6Mg2) also was observed. The effect of trace Zr and Zn elements on promoting strengthening phase’s precipitation, fining the size of precipitates and improving precipitates volume fraction was obviously greater than that of Ce, and delayed the cubic phase (σ) precipitation in a certain extent.4、Mechanical properties tests of alloys after aged at T8(150℃) demonstrated that different predeformation had an important effect on reinforcement of alloy. The greater prestress obtained, the shorter artificial ageing time become. The reinforcement effect of6%predeformation alloy was the best,2%predeformation alloy was in the middle and10%predeformation was the worst. The peak ageing strength and ductility of6%predeformation alloy were:σb=698.2MPa, σ0.2=653.4MPa,8=6.1%; those of2%predeformation alloy were:σb=687.8MPa, ao.2=621.8MPa,8=7.2%while those of10%predeformation alloy were:σb=642.1MPa, σ0.2=582.6MPa, δ=6.2%.5、The regulations of predeformation on regulations of C alloy electrical conductivity with aging time was still6%predeformation>2%predeformation>10%predeformation.6、Different predeformation did not make changes on types of alloy precipitates and the main precipitating phases of alloys were still T1,θ’ and a small amount of Al3Zr or composite particles of Al3Zr with Al3Li. The precipitating volume fraction, size and distribution of T1precipitates were the largest, smallest and most uniform in these alloy samples with6%predeformation and followed by alloys with2%predeformation; while the density and size of precipitating phases for alloys with10%predeformation were relatively little and large.7、The tensile fractures of samples with2%and6%predeformation were mainly based on dimples morphologies types of transgranular crack and the number of dimples in tensile fracture of alloys with6%predeformation was even more and these dimples distributed more uniformly. However, the morphologies of tensile fracture in10%predeformation alloy were entirely distinct; the fracture mode of alloy with10%predeformation mainly consisted of obvious delamination morphology of intergranular-trasngranular crack followed by some cleavage crack.