Effect of Lithium Content on Microstructure and Properties of Al-Si-Mg-Li Alloys

The effect of Li content on microstructure and property of the Al-7Si-0.5Mg alloys were investigated.Alloys were melted in a vacuum resistant furnace.Microstructure was observed by optical microscopy,DSC was employed to determine the phase precipitation by differential scanning calorimeter,and hardness was measured by Vicker's hardness tester.The results show that primary Si phase appeared in the microstructure of Al-Si-Mg-Li containing 7%Si.Primary Si phase changed from oval to triangle shaped and its amount and size increased with the increment of Li.Precipitation phases were inhibited that made the alloys being hardened poorly by ageing.With the Li addition the alloys were lower in elongation and higher in strength,and the elongation decreased with increase of Li content.The alloys containing 2% Li has the maximum strength of 245 MPa.