Research Of Mg₂Si/Al-20%Si In-Situ Composites And Complex Modifier

Mg₂Si reinforced hypereutectic Al-Si alloy in-situ composites have the lower expanding and density behavior, the higher resistance to wear and corrosion and excellent conduct. But before appropriate modification and heat treatment, the size of Mg₂Si larger, it will reduce the mechanical and machining properties due to its brittleness and the dissevering effect to the matrix. So the hypereutectic Al-Si alloy can't been widely applied because of those disadvantages. Based on the size of Si and Mg₂Si in Al-10%Mg-20%Si alloy with different types modifier, we found a new modifier:Ln₂O₃ + CaCO₃ , and gives the good experimental craft parameter. Then use those modified the hypereutectic Al-Si alloy with different Mg contents, Finally, researched the microstructure and properties of Al-Mg-Si alloy under compound modification and T6 heat treatment.Analysis Microstructure we found: the size of primary Mg₂Si reduced from about 75μm to below 25μm, and the shape rules, uniform distribution. The better modification parameters is:the modifier adding quality is 0.5wt.% of the total amount of alloy(Ln₂O₃ is 0.2%,CaCO₃ is 0.3%);modification time is 10min;modification temperature is 820℃. With the increase of Mg content, modifier also increased. The Al-10%Mg-20Si modified with Ln₂O₃ + CaCO₃ and then T6 heat treatment, the degree of dispersion further intensify. Most of the microstructure size under 10μm. And the mechanical capability improved rapidly.In this article, the innovation point is that a new compound modification (Ln₂O₃ + CaCO₃) has been found, and the result notable.