Research Of Melt Complex Treatment Technology On Casting Al-Si Alloys

Through melt thermal-rate treatment (MTRT) on hypereutectic Al-Si alloy, differentmelt temperatures and holding times in MTRT on the microstructure and properties werestudied. Results show that different melt temperatures and different holding times in MTRThave different effects on the microstructure and properties of the alloy. When Al-15Si-2.7Fealloy is treated with MTRT by930℃melt for20min: the coarse primary Si and plate-likeFe-containing phase both can be refined to small blocky morphology, and the long needle-likeFe-containing phase disappears almost entirely, ultimate tensile strength, elongation andhardness of the alloy increase by12.7%,38.5%and10%respectively. Corrosion resistance ofthe alloy treated with MTRT by930℃melt is also the best, that it has the lowest icorrvalueand the highest Ecorrvalue and the wear loss and coefficient of friction decrease7~17%and24~30%respectively, compared with that of the alloy obtained with conventional castingtechnique.MTRT in a low pouring temperature, the primary Si and eutectic silicon of the Al-15Sialloy can be well modified and its tensile properties are improved, the ultimate tensilestrength and elongation are201MPa and3.5%, and increase by12%and25%respectively,compared with that of the alloy obtained by conventional casting technique. In addition, theeutectic growth temperature difference of the alloy treated with MTRT in a low pouringtemperature increases to5.1℃, which is larger than that modified with Sr or RE addition. Itis also indicates that the modification effect of MTRT in a low pouring temperature onAl-15%Si alloy is better than that modified with Sr or RE addition.MTRT in a low pouring temperature can also refine the microstructure and improvemechanical properties of Al-15Si-2.7Fe alloy, but it has no regularity and limitedimprovement. The mechanical properties are also lower than that with MTRT in ordinarypouring temperature. With the holding time at730℃increasing, the size of the Al-Si-Feintermetallic increases, the hardness of the alloy decreases gradually. When the holding timereaches20min, although the hardness of alloy is still down, the change is no longer apparent. Melt complex treatment technology, which is MTRT combining with the modification ofP and RE, can refine primary Si from about100μm to less than10μm and turn eutecticsilicon into short rod-like or granular shape from coarse long acicular morphology of theAl-18Si-1.5Cu-0.6M alloy. In addition, the tensile strength and hardness of the alloy are highto287MPa and102HB, increase by55.1%and70%respectively compared with that of thealloy obtained by the conventional casting technique.Adding Mn element alone can not completely prevent the emergence of acicularFe-containging phases in the alloy, Mn/Fe in a high ratio can form large and regular hexagonblock phase and reduce the mechanical properties of the alloy. MTRT combining with Mncan greatly refine the microstructure and improve its mechanical properties of Al-15Si-1.7Fealloy. When Al-15Si-1.7Fe alloy is treated with2.5Mn and MTRT, the tensile strength andhardness of the alloy are202MPa and88.9HB respectively, compared with that without Mnneutralizing agent and MTRT increase by16.7%and8.3%respectively.