Study On Fabrication Of Hyper-eutectic Al-Si Alloys Using Controlled Diffusion Solidification

Hyper-eutectic Al-Si alloy have several advantages, high hardness, lower density, lower linear expansibility, so they are widely used in moto areas and aviation areas. Espesialy in moto areas, according to the characteristic of hyper-eutectic Al-Si alloy, they can be made to moto pistons and engine blocks and wear resistance parts. These parts can increase the efficiency of engines, also make the moto lighter, and decrease oil quantity. However, during the forming process of hyper-eutectic Al-Si alloys, because of their large solidification range, high silicon fraction, high latent, primary silicon easily grow to large size. The large size of primary silicon heavily seprate Al substrate, so it increases the alloy brittleness, decreases the mechanical property and cutting property of the parts, which limit its widely used. Many overseas scholars have done a lot of researches on how to diminish the size of primary silicon, how to improve the morphology and distribution of primary silicon in the part. Up to now, there are two general ways to refine the primary silicon: modification and improved casting ways. As to modification, it main refers to add phosphorus and rare-earth element to liquid alloy. The ways to cast hyper-eutectic Al-Si alloy are extrution casting, semi-solid casting, rapid solidification, solid-liquid mixing casting and temperature treatment et.al.To prepare hyper-eutectic Al-18%Si,Al-20%Si alloy, the Diffusion Solidification is used in this study.Selecting ZL102,pure Al and Al-25%Si as raw materials,effect of mixing ways (Solid-liquid mixing, liquid-liquid mixing, semsolid-liquid mixing),casting temperuture,pretreatment temperature of raw materials during Controlled Diffusion Solidification process on the microstructure of size, morphology and distribution of primary silicon has been studied.The results show that:(1) Diffusion Solidification can refine the size of primary silicon and improve the morphology and distribution of primary silicon for hyper-eutectic Al-18%Si and Al-20%Si alloy; (2) At the same mixing ways, different pretreatment temperature of raw material have different grain refining effectiveness.To make the refining effectiveness act at the most, it must control the pretreatment temperature at the best state. Only the suitable pretreatment temperature of raw materials can acquire finer grain size and evener distribution microscopic structure;(3) Using ZL102,pure Al and Al-25%Si as raw materials, fine grain size of primary phase of hypereutectic Al-18%Si and Al-20%Si alloy can be got when the mixing ways,casting temperature and pretreatment temperature are all suitable;(4) Because of its simplicity of operation,shorter process and lower cost fabrication of hyper-eutectic Al-18%Si and Al-20%Si alloys using Controlled Diffusion Solidification has a certain degree of progress and superiority.