INFLUENCE OF PHOSPHORUS ADDITION ON THE MICROSTRUCTURE OF IN-SITU Al-25 WT.% Mg2Si COMPOSITE

In current research, the effects of different concentrations of P (0, 0.05, 0.1, 0.3, 0.5, 0.7 and 1 % wt.) on the microstructures of Al-25%wt. Mg2Si composite have been investigated. Microstructural examination was carried out by using optical and scanning electron microscopy (SEM). As-cast microstructure analysis of the composite indicated that the primary Mg2Si phases are very coarse with average size of 200μm. Also the results show that P addition changes the morphology of primary Mg2Sifrom irregular to polygonal or spherical shapes and decreases size of primary Mg2Si particles from200μm to 20 μm in 1%wt. added P specimen. Furthermore, the morphology of eutectic Mg2Si phases changes from fibriform to short fibriform or dot-like. With the addition of P, it reacts with Al to produce particles of AlP phase. The AlP particles can be appropriate sites for heterogeneous nucleation of Mg2Si. It is believed that P addition has strong influence on the nucleation process of primary Mg2Si particles and the subsequent formation of the α-Al phase and the eutectic matrix.

Keywords:

Al/Mg2Si , Phosphorus , Modification , Casting