Creep Age Forming Effect On The Properties Of 2124 Aluminum Alloy, Microstructure And Springback

The heat-treatable2xxx aluminum alloy often used to produce the aerospace application, which must be required to possess high strength, high fracture toughness, heat resistance, corrosion resistance, high resist fatigue crack growth and other many advantages. And the creep aging forming (CAF) technology always uses for manufacturing the aerospace application (such as the palne wing component). This paper based on2124Al alloy hot-rolled plate, the SCAF, DCAF and VCAF treatment have been developed by utilizing the mould of single curvature and double curvature. In order to comparative studies the influence of CAF and CA on the microstructure and properties, the creep aging experiments was developed on the RWS50electronic creep experiment machine and the100KN creep testing machine. After that, creep springback, microstructure, mechanical property and anisotropy, fracture toughness and fracture mechanism have been studied by optical microscopy (OM), transmission election microscopy (TEM), room temperature tensile experiment, Kahn tearing test and scanning electron microscope (SEM). The main conclusions are as follows:(1) The influence of CAF to springback was revealed. High creep aging temperature and long time could restrict the springback of sheet material. It is found that the springback could be controlled by reasonably regulating of temperature and time while the alloy performance without prejudice. When the radius of curvature is1000mm, the window of the springback is controlled between50%and70%, the springback of the2124Al alloy plate is51.7%at DCAF/185℃/12h. CAF with vibrational stress relief could effectively reduce the springback, and the springback was minimum at VCAF/185℃/12h, which is41.6%. Comparing to the DCAF/185℃/12h treatment, the alloy springback of VCAF/185℃/12h decrease by24.3%.(2) The main strengthening phase of2124Al alloy was S’ phase by CAF treatment, which had the same exsolution sequence to the artificial aging. Observing from [100]AI direction, the S’phase with cross shape distribution by SCAF, DCAF and VCAF treatment. At the same time, the so called stress oriented effect can not find in our observation. What is more, the vibrational stress relief can control the position and quantity of precipitation of S’ phase and increases the volume fraction of S’phase of VCAF alloy, which made it more compact and uniform.(3) The influence of CAF to mechanical property and anisotropy was explored. With SCAF and DCAF treatment, the time, temperature and initial bending state can affect the strength of2124Al alloy. With the increase of temperature, the strength of alloy increases at the early stage then decreases, but the elongation constantly decreases. Under the same aging condition, the strength of DCAF alloy is higher than SCAF alloy. The strength of2124Al alloy with DCAF treatment attained to477.4MPa. The mechanical property of CAF alloy could be enhanced by introducing vibrational stress relief, the highest strength of the alloy at VCAF/185℃/9h treatment, whose tensile strength is495.7MPa, yield strength is428.5MPa. The strength anisotropy of sheets are not obvious by CAF, IPA values are less than10%, but the anisotropy of elongation is obvious, which can up to23.6%. The anisotropy of mechanical property of2124Al alloy with DCAF treatment is less than the alloy with SCAF treatment, while the VCAF treatment has the least anisotropy.(4) The influence of CAF to fracture toughness and fracture mechanism was established. The fracture toughness of SCAF and DCAF alloy decreases constantly with the increase of aging temperature, while the difference of UIE values between the SCAF alloy and the DCAF alloy is not obvious at the same aging condition. The fracture toughness of CAF samples have obvious anisotropy, the45°direction possess the highest fracture toughness, followed by at the90°direction, and the least fracture toughness at0°direction. The fracture mechanism is combination of dimple fracture and intergranular fracture. With the increase of temperature, the dimple fracture decreases constantly, so do the dimples. At the same time, the intergranular fracture increases constantly. After CAF treatment of2124aluminum alloy with vibrational stress relief, which can not only increase the fracture toughness but also decrease the anisotropy of fracture toughness, which makes the formed samples more stable.(5) when the creep aging at185℃/150MPa, the turning point between the first stage and the second one along the creep curve is easily observed for the samples with an initial state of solution-water quenching (QCA), the characters of TEM micrographics show that the dislocation multiplication (DM) and the balance between DM and dislocation annihilation (DA) occur. While the turning point along the creep curve is difficultly identified for the samples with the initial state of solution-water quenching-rolling to thickness reduction rate of8%(PCA), the microstructures of TEM reveal that DA mainly occurs. During the processes of creep-aging, it is found that the precipitating S’ phase particles always nucleate with dislocation lines, and their orientations are effected by characteristics of dislocation moving. During PCA process, the existing of dislocation tangling by the rolling before the creep aging supports precipitating S’phase on vertical{210} planes, therefore, the stress orientated effect of S’phase is restrained. The mechanical properties of PCA sample are well than that of the as T6and T87, and the anisotropy of mechanical properties is less than that of the as QCA.