Abstract:The microstructural evolution of Al-0.66Mg-0.85Si alloy was investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The as-cast microstructure is typical dendritical structure, consisting of α(Al), Al(FeMn)Si, Mg₂Si, AlCuMgSi and Si phases. The electron diffraction analyses indicate that the Al(FeMn)Si phase is Al₁₅(FeMn)₃Si₂ and the AlCuMgSi phase is Q(Al_1.9CuMg_4.1Si_3.3). There are two kinds of Mg₂Si phases in the as-cast microstructure. One is formed in the casting process, and the other is formed in the cooling process after casting process is finished. The phases have different crystal structures. After homogenization treatment at 545 °C for 20 h, Mg₂Si, Si and Q intermetallic compounds are dissolved into matrix completely, and the remaining phases are α(Al) and Al₁₅(FeMn)₃Si₂. The size of Al₁₅(FeMn)₃Si₂ phase is decreased, and the phase is spheroidized and distributes along grain boundary discontinuously. The Zn-containing phases are not found during solidification and homogenization process.

Key words: Al-Mg-Si alloy; microstructural evolution; homogenization; intermetallic compound