Mn含量及冷却速率对真空吸铸Al-Mn合金显微组织的影响

Effects of Mn content and cooling rate on microstructure of vacuum suction casting Al-Mn alloy

分别利用TEM,SEM,XRD分析Mn含量(质量分数,下同)及冷却速率对真空吸铸Al-Mn合金中Al6Mn相形貌的影响.结果表明:在Al-Mn合金中,树枝状Al6Mn相的枝晶夹角均为72°,随着Mn含量的改变,Al6Mn相形貌和析出量也在不断变化;Al-4%Mn合金(4%为Mn的质量分数,下同)中的Al6Mn相呈块状且析出量较少;Al-6%Mn和Al-8%Mn合金中的Al6Mn相呈块状和针状,析出量随合金中Mn含量的增加而增多;Al-10%Mn合金中的Al6Mn相呈树枝状和针状且大量析出,但二次枝晶臂退化严重,这是由于在真空吸铸过程中形成了二十面体的准晶相.此外,冷却速率的增大促进了Al-Mn合金中树枝晶析出,但抑制了星状析出相的生长,其外轮廓等效直径减小.

The effects of Mn content(mass fraction,same as below)and cooling rate on the morphology of Al_(6)Mn phase in vacuum casting Al-Mn alloy were analyzed by TEM,SEM,and XRD,respectively.The results showed that the dendrite angle of the dendritic Al_(6)Mn phase in Al-Mn alloy was 72°.With the change in Mn content,the morphology and precipitation amount of Al_(6)Mn phase also changed continuously.In the Al-4%Mn alloy(4%was the mass fraction of Mn,same as below),the Al_(6)Mn phase was massive and the precipitation amount was small.In Al-6%Mn and Al-8%Mn alloys,Al_(6)Mn phase was massive and acicular,and the precipitation amount increased gradually with Mn content increasing.In the Al-10%Mn alloy,a lot of precipitated Al_(6)Mn phase was confirmed,whose morphology was dendritic or acicular but with seriously degenerated secondary dendrite arms,which was due to the formation of icosahedral quasicrystalline phase during the vacuum casting process.In addition,the increase of cooling rate promoted the dendrite precipitation in Al-Mn alloy but inhibited the growth of the star precipitates,and its outer contour equivalent diameter decreased.