Effect Of RE Element Nd On Microstructure And Mechanism Properties Of Hyper-eutectic Aluminum Silicon Alloys

The paper investigated the modification effect of rare earth to the primary silicon of hypereutectic Al-Si alloy. Experiment materials were prepared by routine cast process and the modification effect to hypereutectic Al-Si alloys with different Si content were investigated. In this paper Al-17.5Si,Al-25Si alloy and A390 hypereutectic aluminum silicon alloys were selected to investigate the effect of RE Nd addition,heat treatment and extruding processing on microstructure and mechanical of these alloys by XRD, SEM and mechanical properties test. The relations between microstructure and mechanical properties and modifcation mechanism were discussed and presented a new way to fabricate high performance hypereutectic Al-Si alloy.The experiment results show that pure Nd (0.3wt%) can refine both eutectic silicon and primary silicon in binary hypereutectic Al-Si alloy. The modification mechanism of primary silicon can be explained reasonably by undercooling theory and adsorbing theory simultaneously. There is no obviously change in morphology of primary silicon in Al-17.5Si alloy after modification, but after Nd modification treatment the average size reduced from 34.73μm to 23.39μm, mechanical properties of tensile and yield strength reach 240MPa and 130MPa increased 11.6% and 1.5% respectively; the abrasive wear and tear rate of the modified alloy reduced 51.1%. The morphology of primary silicon Al-25Si alloy change from star-sharped and irregular to plated sharp after modification, and the average size reduced from 94.06μm to 50μm. The tensile and yield strength of Al-25Si modified alloy reach 117.5MPa and 94MPa and were improved 22.1% and 9.5% respectively, the wear rate of the modified alloy reduced 66.7% and the coefficient of friction reduced obviously. The morphology of eutectic silicon particles in Al-25Si-0.3wt%Nd alloy granulate after heat treatment. The experiment results show that the addition of rare earth Nd has little modification effect on primary silicon phases in A390 alloy, as expected for the formation of the compounds of Cu2NdSi reduced modification effect of rare earths, after heart treatment the eutectic silicon spheroidized in A390, the plastic property of A390 alloy improved dramatically and elongation percentage increased from 0.5% to 13.25%.It is the first time to propose that modification effect of Nd element on varying morphology primary silicon is different. the results supplied a new way to develop high mechanical properites hypereutectic Al-Si alloy.