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采用搅拌摩擦加工技术(friction stir processing,FSP)成功制备出平均晶粒尺寸为600 nm的超细晶2024铝合金,观察和测量了超细晶材料不同温度退火后的显微组织及室温力学性能,对超细晶材料的热稳定性进行研究,研究发现:当温度为150~200℃时,超细晶铝合金呈现退火强化现象,力学性能较退火前略有提高;当温度为250~350℃时,晶粒及析出相长大导致细晶强化及第二相强化作用减弱,超细晶材料的热稳定性较差。随着温度的升高,超细晶铝合金的晶粒和析出相逐渐粗化,呈现明显的软化现象。当温度为400℃时,细晶铝合金的晶粒尺寸已经超过2μm,受到高温固溶强化效应作用,材料的抗拉强度比350℃加热试样的抗拉强度提高了54 MPa。结果表明:退火温度为200℃时,超细晶材料的热稳定性最佳,超细晶材料的平均晶粒尺寸为0.807μm,硬度为HV110.7,抗拉强度为359 MPa。
The ultrafine-grained 2024 aluminum alloy with an average grain size of 600 nm was successfully prepared by friction stir processing (FSP). The microstructure and room-temperature mechanical properties of the ultrafine-grained material after annealing at different temperatures were observed and measured , The thermal stability of the ultrafine-grained material was studied. The results show that the ultrafine-grained aluminum alloy exhibits an annealing strengthening phenomenon at 150-200 ℃, and its mechanical properties slightly increase when compared with that before annealing. When the temperature is 250-350 ℃ , The growth of grain and precipitated phase leads to the weakening of the fine grain strengthening and strengthening of the second phase, and the poor thermal stability of the ultrafine grain material. With the increase of temperature, the grains and precipitates of ultrafine-grained aluminum alloy gradually roughened, showing obvious softening phenomenon. When the temperature is 400 ℃, the grain size of the fine-grained aluminum alloy has exceeded 2μm and the high-temperature solid solution strengthening effect makes the tensile strength of the material increased by 54 MPa compared with that of the sample heated at 350 ℃. The results show that the best thermal stability is obtained when the annealing temperature is 200 ℃. The average grain size of the ultrafine grained material is 0.807μm, the hardness is HV110.7 and the tensile strength is 359 MPa.