Al-1.2Cu-3.5Li-(0.02Yb)合金多级均匀化退火工艺及其显微组织研究

Study on multi-stage homogenization annealing process and its microstructure of Al-1.2Cu-3.5Li-(0.02Yb)alloys

对Al-Cu-Li-(Yh)合金的均匀化退火过程微观结构的研究是设计高强铝锂合金及其时效处理的基础。采用金相显微镜(0M)、差热分析(DSC)、X射线衍射(XRD)、扫描电镜(SEM)和能谱(EDS),研究了Al-1.2Cu-3.5Li-(0.02 Yb)合金多级均匀化工艺及均匀化过程中微观组织的演变。结果表明:合金铸态组织存在晶界沿晶和晶内球形一次相,以及枝晶偏析,其中Al-1.2Cu-3.5Li合金析出相由Al17Cu4Li、Al2CuLi和AlCuFe组成,AM.2Cu-3.5Li-0.02Yb合金析出相由Al7CU4Li、Al2CuLi、Al2CU和AlCuYb组成。为了让析出相尽可能的回溶,同时避免过烧,Al-1.2Cu-3.5Li和Al-1.2Cu-3.5Li-0.02Yb合金分别设计了500T12 h+550℃12 h两级均匀化和500℃12 h+560℃12 h+580℃12 h三级均匀化退火。均匀化退火后枝晶偏析基本消除,晶界相和晶内球形相部分回溶。值得注意的是,球形相回溶后,分解为多个细小的球形颗粒,对于Al-1.2Cu-3.5Li合金和Al-1.2Cu-3.5Li-0.02Yb合金,残留相分别为AlCuFe和AlCuYb相。

The study on microstructure of Al-Cu-Li-(Yb)alloy during homogenization annealing is the basis for designing high strength Al-Li alloy and its aging treatment.The multistage homogenization process and its microstructure evolution of as-cast Al-1.2Cu-3.5 Li-(0.02 Yb)at.%alloys were studied using OM(Optical Microscope),DSC(Differential Scanning Calorimeter),XRD(X-ray Diffraction),SEM(Scanning Electronic Microscopy)and EDS(Energy Dispersive Spectrometer).The results indicate that the alloys in the as-cast states show the dendrite segregation,and contain primary precipitates along grain boundary and intragranular with the spherical shape.Wherein,the primary phases of Al-1.2Cu-3.5Li alloy are Al7Cu4Li,Al2CuLi and AlCuFe,and the primary phases of Al-1.2Cu-3.5Li-0.02Yb alloy are Al7Cu4Li,Al2CuLi,Al2Cu and AlCuYb.In order to dissolve the primary phase as much as possible and avoid over-burning at the same time,two-stage homogenization annealing at 500℃ 12 h+550℃ 12 h and three-stage homogenization annealing at 5008C12 h+560℃12 h+580℃12 h were designed for Al-1.2Cu-3.5Li and Al-1.2Cu-3.5Li-0.02Yb alloys,respectively.After annealing,the dendrite segregation basically disappear,and the grain boundary phase and intragranular spherical phase are partially dissolved.It should be noted that after the dissolution of the spherical phase,during homogenization,each single primary spherical phase decomposes into many fine spherical particles,and the residual phases of Al-1.2Cu-3.5Li and Al-1.2Cu-3.5Li-0.02Yb alloys are Al-CuFe and AlCuYb,respectively.