Effects Of Modification On Microstructure And Machinability In Hypereutectic Al-Si Alloys

The hypereutectic aluminum-silicon alloys have series of characteristics, such as high wear resistance, high heat resistance, low expansibility and good size stability etc, and it has been the important materials of manufacturing engine cylinder, piston and other parts. So it widely used in aerospace, automobile manufacturing and other fields. However, the coarse primary crystal Si phase existed in hypereutectic Al-Si alloy seriously fragmented the matrix, deteriorated the mechanical properties and limited its wide application in industry. An effective way to solve such problems is to modification the primary crystal Si phase, so improve its machinability.In this paper, optical microscope, metalscan2000/2000F type emission spectroscopy, mechanical properties testing and the analysis methods of modeling evaluation were used. This paper systematically investigate the effects of modification on microstructure and machinability in Hypereutectic Al-20Si alloys.The results show that the hypereutectic Al-Si alloys use P modification and the modification effects can be affected by the amount of modifier added, metamorphic temperature and metamorphic time. When the modifier addition amount is1.0%, the average size of the primary silicon is minimum and the modification effect is best that the size decrease from120μm to25μm. When metamorphic temperature above760℃, the effect is obvious and the average size of primary silicon is about30μm. While metamorphic temperature below760℃, modifier can’t be fully metamorphism. When the metamorphic time is1h, the average size of primary silicon is about25μm and the modification is better. However, when the metamorphic time is more than1h, the average size of primary silicon become larger with the time increase. By the orthogonal experiment, the best modifying technology parameters of P modification hypereutectic Al-Si alloys are that the modifier addition amount is1.0%and metamorphic temperature is760℃and the metamorphic time is1h.After modification of hypereutectic Al-Si alloy, the hardness from138.7HB up to167.7HB, increased by about20.9%. And the elongation rate become from0.2%to0.4%.What’s more, the abrasion resistance is reduced. After the modification machinability Radar larger than before modification, this prove that machinability improve after modification. The tool life is1.75times than before, average friction decrease about8.4%, friction-time curve becomes smooth, weight loss becomes small and productivity increase. Those results show that modification can improve hypereutectic Al-Si alloy machinability.