采用透射电镜、电子探针、拉伸和硬度测试等方法对铸态Al-6Mg-0.2Sc-0.15Zr(质量分数, %)合金在等温退火过程中的硬化行为进行了研究. 结果表明, 退火过程中Mg分布的变化对合金强度影响不大,细小、弥散的Al3(Sc, Zr)沉淀相的析出产生了显著的沉淀强化作用.合金在300 ℃下退火, Al3(Sc, Zr)沉淀相粗化速率较慢,经过24 h处理后其直径为5 nm, 合金屈服强度相对退火前提高约90 MPa;随着退火温度的升高, Al3(Sc, Zr)相在退火过程中发生不同程度的粗化.450 ℃/24 h处理后沉淀相直径增大至约30 nm, Al3(Sc, Zr)相引起的沉淀强化作用下降至30 MPa. 铸态Al-6Mg-0.2Sc-0.15Zr合金经过 300 ℃/3 h退火处理后可获得最大的沉淀强化效果.
Addition of minor Sc and Zr to the Al–Mg alloys can effectively improve the recrystallization temperature and strength of the alloys due to the formation of L12 structured Al3(Sc, Zr) precipitates. To optimize the mechanical properties of the Al–Mg–Sc–Zr alloys, it is important to understand the precipitation behavior of the Al3(Sc, Zr) precipitates and the corresponding strengthening effect during the annealing of Al–Mg–Sc–Zr alloys. In this work, isothermal annealing at the temperatures between 250 and 450 ℃ was conducted to study the precipitation behavior of Al3(Sc, Zr) particles in the as–cast Al–6Mg–0.2Sc–0.15Zr alloy (mass fraction, %). The results show that dramatic precipitation hardening occurred with the formation of the coherent Al3(Sc, Zr) precipitates during the annealing. Precipitation rocess of the Al3(Sc, Zr) accelerates with the increase of the annealing temperature. After the sample was annealed at 300 ℃ for 24 h, the Al3(Sc, Zr) particles were in a size of 5 nm ad the yield strength of the as–cast alloy can be increased by 90 MPa. Severe coarsening of Al3(Sc, Zr) occurred when the annealing temperature is bove 400 ℃. After annealed at 450 ℃ for 24 h, average particle size of Al3(Sc, Zr) particles was found increase to 30 nm, wth the corresponding precipitation strengthening effect to be about 30 MPa.
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