摘要
The microstructural evolution of a Mg, Ag and Zn micro-alloyed Al?3.8Cu?1.28Li (mass fraction, %) alloy ingot during two-step homogenization was examined in detail by optical microscopy (OM), differential scanning calorimetry (DSC), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) methods. The results show that severe dendritic segregation exists in the as-cast ingot. There are many secondary phases, includingTB(Al7Cu4Li),θ(Al2Cu),R(Al5CuLi3) andS(Al2CuMg) phases, and a small amount of (Mg+Ag+Zn)-containing and AlCuFeMn phases. The fractions of intermetallic phases decrease sharply after 2 h of second-step homogenization. By prolonging the second-step homogenization time, theTB,θ,R,S and (Mg+Ag+Zn)-containing phases completely dissolve into the matrix. The dendritic segregation is eliminated, and the homogenization kinetics can be described by a constitutive equation in exponential function. However, it seems that the AlCuFeMn phase is separated into Al7Cu2Fe and AlCuMn phases, and the size of Al7Cu2Fe phase exhibits nearly no change when the second-step homogenization time is longer than 2 h.
利用光学显微镜(OM)、差示扫描热分析法(DSC)、电子探针(EPMA)、X衍射(XRD)等研究手段分析Mg、Ag、Zn复合微合金化的Al-3.8Cu-1.28Li(质量分数,%)合金在均匀化过程中的组织转变。结果表明:合金的铸态组织中存在严重的枝晶偏析,此时合金中含有TB(Al_7Cu_4Li)、θ(Al_2Cu)、R(Al_5CuLi_3)、S(Al_2CuMg)相以及少量的(Mg+Ag+Zn)复合相与AlCuFeMn相。当第二级均匀化时间为2 h时,第二相含量大幅度降低。随着均匀化时间的延长,T_B、θ、R、S和(Mg+Ag+Zn)复合相能全部溶入基体,从而合金的枝晶偏析消除,且合金的均匀化过程可以用一指数方程描述。但是AlCuFeMn相似乎转变成Al_7Cu_2Fe和AlCuMn相,其中Al_7Cu_2Fe的尺寸几乎不发生变化。
基金
Project(2013JSJJ0001)supported by Teachers’Research Found,China
Project(2013AA032401)supported by the National High Technology Research and Development Program of China
Project supported by the Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center,China
