激光定向能量沉积制备 2195 铝锂合金构件成形与组织性能研究

Objective Aluminum-lithium alloys feature high specific strength, specific stiffness, and damage tolerance, and have great application potential in the aerospace field. In this study, the thin-walled components of 2195 aluminum-lithium alloys are prepared by laser directional energy deposition (LDED) technology. The morphology and quality of the deposited layer are optimized through single-factor experiments. The microstructure evolution laws of the deposited state and heat-treated state samples are systematically analyzed, and the mechanical property tests are conducted on them. It is expected to provide theoretical support and technical reserves for achieving high-performance laser additive manufacturing of aerospace-grade aluminum-lithium alloy components. Methods The LDED system consists of a fiber laser, a laser head, a wire feeder, and a six-axis robot. A single-channel single-factor deposition test is conducted, and high-purity (mass fraction of 99.99%) Ar with a flow rate of 25 L/min is used to protect the molten pool. Before deposition, the oxide layer on the 2195 substrate is removed with sandpaper, and oil and impurities are removed with anhydrous ethanol. The characteristic parameters of the monolayer deposition samples are obtained based on the single molten channel experiment. Subsequently, a single-pass multi-layer deposition test is conducted using the well-formed process parameters, with interlayer cooling for 60 s. As shown in Figs. 1 (a) and (c), a 60-layer thin-walled component with the dimension of 140 mm× 50 mm×4 mm is fabricated. In this paper, T6 heat treatment is carried out by solution treatment (515 ℃/90 min) + aging (170 ℃/6 h). Results and Discussions For the preparation of thin-walled components of 2195 aluminum-lithium alloys by laser melting and deposition, a well-formed deposition layer can be obtained when the liquid bridge transition method is adopted and the laser power and the scanning speed are 2000‒2200 W and 1.0‒1.2 m/min, respectively (Figs. 2, 3, 4, 5 and 6). The sedimentary state specimens are mainly composed of α -Al and θ -Al₂Cu. After T6 heat treatment, the sample is mainly composed of α -Al. No obvious diffraction peaks, which are characteristic of the Al₂Cu phase, are found. There are no obvious enrichment areas of Cu, Ag, Mg, and Zr elements in the sample, but they are uniformly distributed in the α -Al matrix. The strip-shaped and fine precipitated phases in the sample disappear, and the Al₂Cu phase is solidly dissolved into the Al-Li alloy matrix (Figs. 8, 9 and 10). The mechanical properties of the deposited aluminum-lithium alloy show anisotropy in the parallel deposition direction (OY direction) and the vertical deposition direction (OZ direction) (Fig. 11). The fracture surface presents large and shallow dimples, and at the same time, the cleavage planes exist, showing the characteristics of mixed ductile and brittle fractures. After heat treatment, intergranular fracture occurs during the stretching process, with the surface showing the characteristics of brittle fractures. The maximum tensile strength is 325 MPa, and there are pore defects at the fracture surface (Figs. 12 and 13). Conclusions The microstructure of the deposited aluminum-lithium alloy components has fine columnar crystals in the bottom area, columnar grain formed along the direction of the maximum temperature gradient in the lap area, and the fine equiaxial grain in the top area. The X-ray diffractometer (XRD) and scanning electron microscope (SEM) show that the deposition state is mainly composed of the α-Al matrix and the θ-Al₂Cu phase. After T6 heat treatment, the θ phase disappears and the Cu element is uniformly dissolved in the α-Al matrix. The tensile strengths of the deposited state in the OY direction and the OZ direction are 158 MPa and 271 MPa, respectively. The tensile strengths of the T6 state specimens in the two directions are 233 MPa and 325 MPa, respectively. The mechanical properties of the T6 state specimens are significantly improved. At the same time, it is found that there is a strong anisotropy in the tensile properties of laser-directed energy deposited aluminum-lithium alloys.