摘要
An optimized combination of gamma alumina (4 wt.%) and strontium (0.1 wt.%) was incorporated in cast Al-20Si alloy to obtain fine form of silicon. During casting process, the amount of γ-Al2O3 was varied from 0.5.6 wt.% to refine primary Si and Sr was varied from 0.05.0.1 wt.% to modify eutectic Si. The results showed that the average size of primary Si is 24 μm for addition of 4 wt.%γ-Al2O3 to the alloy whereas 0.1 wt.% Sr resulted in sphericity of eutectic Si to ~0.6 and average length of ~1.2 μm. The thermal analysis revealed that γ-Al2O3 can act as potential heterogeneous nucleation sites. Moreover, simultaneous addition of γ-Al2O3 and Sr does not poison γ-Al2O3 particles and inhibit their nucleation efficiency as in the case of combined addition of phosphorous and strontium to Al-20Si alloy. Therefore, it was concluded that enhanced tensile strength, i.e., ultimate tensile strength (increase by 20%) and elongation (increase by 23%) in Al-20Si.4γ-Al2O3.0.1wt.%Sr alloy as compared to as-cast Al.20Si alloy can be attributed to refinement of primary Si, modification of eutectic Si and the presence of α(Al) in the alloy as evident from eutectic shift.
为得到细晶硅,向铸造Al-20Si合金中加入4%(质量分数,下同)γ-Al2O3和0.1%Sr。在铸造过程中,γ-Al2O3的作用是细化初晶硅,其添加量为0.5%~6%,而锶的作用是改性共晶硅,其添加量为0.05%~0.1%。结果表明,当添加4%γ-Al2O3时,初晶硅的平均尺寸为24μm。当添加0.1%Sr时,共晶硅的形状因子约为0.6,平均长度约为1.2μm。热分析发现γ-Al2O3可以作为潜在的异质形核点。而且,与在Al-20Si合金中同时添加P和Sr一样,同时添加γ-Al2O3和Sr不会污染γ-Al2O3颗粒和抑制他们的形核效率。与铸态Al-20Si合金相比,Al-20Si-4γ-Al2O3-0.1%Sr合金的极限抗拉强度提高了20%,伸长率提高了23%。抗拉强度的提高可归因于初晶硅的细化、共晶硅的改性,以及合金中由于共晶转变而析出的α(Al)。
