In this study the mechanical behaviours of Al-12Si-XMg alloys (where Mg contents varied up to 20%) have been investigated. The alloys were prepared by casting followed by extrusion at 300 degrees C with a ratio of 1.6. Precipitation of the Mg2Si phases was observed in the Mg containing Al-12Si alloys as two different morphologies; i.e., as a polyhedral primary particle and as a Chinese script. Results showed that volume fraction and size of the primary Mg2Si particles increased with increasing the Mg content. Mg containing alloys exhibited higher hardness, compression strength and lower corrosion resistance than the Mg free alloy. (C) 2010 Elsevier B.V. All rights reserved.