搅拌摩擦加工超细晶2024铝合金热稳定性研究

Thermal Stability of Ultra-Fine Grained 2024 Aluminum Alloy Prepared by Friction Stir Processing

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。

Ultra-fine grained 2024 aluminum alloy was obtained by friction stir processing（ FSP）,the average grain size was 600 nm,microstructure and mechanical properties of ultra-fine grained 2024 aluminum alloy at room temperature were observed and measured after annealing at different temperatures,and the thermal stability of ultra-fine grained 2024 aluminum alloy was investigated. It was found that the phenomenon of annealing strengthening occurred at 150 ～ 200 ℃,and the mechanical properties improved slightly;from 250 to 350 ℃,grain refinements strengthening and precipitates strengthening weakened due to that grains and precipitates grew up,and the thermal stability of the ultra-fine grained 2024 aluminum alloy was poor. Grains and precipitates grew rapidly with the temperature increasing,phenomenon of annealing softening occurred. The grain size of the aluminum alloy was larger than 2 μm when the temperature increased to 400 ℃,phenomenon of solution strengthening occurred,and the tensile strength was improved by 54 MPa compared with that at 350 ℃. The results showed that the optimal thermal stability of ultra-fine grained 2024 aluminum alloy was observed at annealing temperature of 200 ℃,the average grain size was 0. 807 μm,microhardness was HV110. 7 and tensile strength was359 MPa.