Experimental study and phase diagram calculation in Al–Zn–Mg–Si quaternary system

The phase equilibrium of the Al–Zn–Mg–Si quaternary system containing (Al), (Si), MgZn2 and Mg2Si phases has been studied by means of scanning electron microscopy (SEM), electron dispersive spectrometry (EDS), X-ray diffraction (XRD) and differential scanning calorimeter (DSC) as well as calculation of phase diagram based on PANDAT software. Two three-phase fields and one four-phase field among the 15 wt% Al–Zn–Mg–6 wt% Si alloys in the concentration of Zn ranging from 57 wt% to 67 wt% have been confirmed at 573 K. The result showed non-existence of quaternary compound in this region. Based on the experimental results, the appropriate thermodynamic description of Mg–Si system was chosen. The ternary interactions in the liquid phase of Al–Mg–Si and Mg–Zn–Si systems have been assessed and the calculated ternary phase diagrams agreed well with the experimental data. Combining with the related ternary systems, the thermodynamic description of the Al–Zn–Mg–Si system was presented, and the good agreement between the calculated results and the experimental results was obtained.