Al-5Ti-B对过共晶Al-18Si合金的变质效果

Effect of Al-5Ti-B alloy on hypereutectic Al-18Si alloy modification

采用Al-5Ti-B变质剂对过共晶Al-18Si合金进行反向变质处理,用光学显微镜观察合金的组织与形貌,研究变质剂加入量、变质温度和冷却速度对初晶硅的尺寸、形态和面积分数以及共晶组织的影响。研究表明:当Al-5Ti-B加入量(质量分数)为0.3%时,变质处理后Al-18Si合金中的初晶硅和共晶硅尺寸明显减小,初晶硅的面积分数减小;与其相比,变质剂加入量增加到0.6%时,初晶硅尺寸变化不明显,但共晶硅进一步细化;随冷却速率降低,变质处理后Al-18Si合金中初晶硅相的数量减少,但Si颗粒尺寸明显增大,并且共晶硅细化;与Al-18Si合金在720℃变质相比,该合金在780℃变质处理时,初晶硅的尺寸增大,但初晶硅的面积分数显著减小;合金在850℃变质处理后初晶硅的尺寸、面积分数都比720℃变质处理后明显减小;随变质温度升高,Al-Si合金中的共晶硅明显细化。

Hypereutectic Al-18 Si alloy was modified through reverse modification treatment using Al-5Ti-B master alloy. The effects of adding amount of Al-5Ti-B, modification temperature and cooling rate on the size, morphology and area percentage of primary Si were investigated by optical microscopy. The results show that when addition mass fraction of Al-5Ti-B is 0.3%, the sizes of primary Si and eutectic Si in Al-18 Si alloy decrease significantly, and the area percentage of primary Si also decreases. With the increase of the addition amount of Al-5Ti-B, there is few changes in the size of primary Si, but eutectic Si can be refined obviously. With the decrease of cooling rate, the size of primary Si increases, but the area percentage of primary Si and the size of eutectic Si decrease. Compared with the Al-18 Si alloy modified at 720 ℃, the size of primary Si increases when Al-18 Si alloy is modified at 780 ℃, but the area percentage of primary Si decreases obviously. When Al-18 Si alloy is modified at 850 ℃, both the size and area percentage of primary Si increase remarkably compared with those modified at 720 ℃. Furthermore, with the increase of modification temperature, the eutectic Si in Al-18 Si alloy is refined significantly.