Al-Mg-Mn-Sc铸态合金退火行为研究

Study on the Annealing Behavior of Al-Mg-Mn-Sc As-cast Alloy

通过水冷铜模急冷铸造法制备了Al-5.5Mg-0.4Mn-0.25Sc合金,研究了该铸态合金在不同退火温度下的硬度变化,并通过金相显微镜和透射电镜探讨合金中Al_(3)Sc粒子的存在形式和形成机理。结果表明:添加质量分数为0.25%的Sc对铸态合金晶粒组织的细化并没有产生太大的贡献,晶粒细化是由于快速凝固技术所带来的作用,在高的冷却速率下,合金中较难发现初生Al_(3)Sc粒子的存在。退火温度对于合金硬度有显著影响,在低的温度下退火时,合金硬度变化较慢,需较长时间才出现硬度峰值;而在较高温度下退火时,合金硬度峰值平台出现需要时间较短,但随着退火时间延长硬度迅速下降。在所测试的退火温度中,300℃下呈现出较好的硬度曲线,具有较高的硬度峰值平台且能维持较长时间不下降。退火过程中合金硬度的变化与次生Al_(3)Sc粒子的析出密切相关,退火温度较低时次生Al_(3)Sc粒子析出不充分、粒径较小,对晶界、亚晶界和位错的钉扎作用较弱;而退火温度太高,Al_(3)Sc粒子发生粗化,导致合金性能变差。

Al-5.5Mg-0.4Mn-0.25Sc(wt%)alloy was casted by water-cooled copper die.The hardness variation of the as-cast alloy annealed at different temperatures was studied.The existence modality and formation mechanism of Al_(3)Sc particles in the alloy were investigated by metallographic microscope and transmission electron microscope.The results show that 0.25wt%Sc does not contribute much to the refinement of as-cast grain structure,and the grain refinement comes from the effect of rapid solidification technology.At high cooling rate,it is difficult to find the presence of primary Al_(3)Sc particles in the alloy.The annealing temperature has a significant effect on the hardness of the alloy.At low annealing temperatures,the hardness of the alloy changes slowly,and it takes a long time to appear the hardness peak.At higher annealing temperatures,the peak platform appears faster,but after this peak the hardness decreases rapidly as the annealing continues.Among these temperature tests,the hardness curve of 300℃is outstanding,which has a higher hardness peak platform and maintains a long time without decreasing.The change of hardness during annealing is closely related to the precipitation of secondary Al_(3)Sc particles.When the annealing temperature is low,the precipitation of secondary Al_(3)Sc particles is insufficient and the particle size is small,and the pinning effect on grain boundaries,sub-crystalline boundaries and dislocations is weak;while the temperature is too high,Al_(3)Sc particles coarsen and result in poor properties.