Al-Mg-Sc-Ti合金中Al3(Scx,Ti1-x)粒子的析出行为

Precipitation of Al(Sc,Ti) Particles in Al-Mg-Sc-Ti Alloy

用激冷铸造法制备Al-5.5Mg-0.25Sc-0.04Ti合金,研究了在不同温度退火后其硬度随时间的变化,并用金相显微镜(OM)和透射电镜(TEM)研究了这种合金中Al3(Scx,Ti1-x)第二相粒子的存在形式和形成机制。结果表明:用急冷铸造法制备的Al-5.5Mg-0.25Sc-0.04Ti铸态合金中Sc和Ti原子主要以固溶的形式存在于α(Al)基体中,在电镜下很难观察到这些粒子。铸态合金在较低温度(低于250℃)下退火时其硬度提高得比较慢,退火较长时间才能出现硬度的峰值;而在比较高的温度(高于350℃)退火硬度提高得非常快,很快出现峰值。但是,硬度出现峰值后继续退火则大幅度降低;在300℃退火硬度的热稳定性比较高。硬度的变化,与次生Al3(Scx,Ti1-x)粒子的析出密切相关。在较低温度下次生Al3(Scx,Ti1-x)粒子的析出不充分且粒径较小,对晶界、亚晶界和位错的钉扎作用较弱;而在过高的温度下Al3(Scx,Ti1-x)粒子发生粗化,使合金的性能降低。

Cast ingot of Al-5.5 Mg-0.25 Sc-0.04 Ti alloy was prepared by chill casting,and of which the hardness change with time at different annealing temperatures was assessed by hard-meter.While the morphology and formation process of the precipitates Al3(Scx,Ti1-x)of the alloy were investigated by means of metallographic microscopy(OM)and transmission electron microscopy(TEM).The results show that Sc and Ti atoms mainly exist as solid-solute in theα-Al matrix when the alloy was made by chill casting,while in such case,precipitates Al3(Scx,Ti1-x)could hardly be observed by electron microscopy.Annealing at lower temperatures(below 250℃)the hardness of as-cast alloy increases slowly,and the hardness peak appears only after a long annealing time.Annealing at higher temperatures(above 350℃)the hardness increases very quickly,and the hardness peak of the alloy appears quickly,but when the hardness peak appears the hardness will decrease greatly as the annealing continues.Among others,the alloy presents the highest thermal stability when annealing at 300℃.The changes in hardness are closely related to the secondary precipitates of Al3(Scx,Ti1-x).If the annealing temperature is lower,the precipitates of Al3(Scx,Ti1-x)is incomplete and their size is smaller,so the pinning effect on grain boundary,subgrain boundary and dislocation is weaker.But when the annealing temperature is higher,the coarsening of precipitates of Al3(Scx,Ti1-x)will occur,it results in poor alloy properties.