Effect of La2O3 in the Al–P–Ti–TiC–La2O3 modifier on primary silicon in hypereutectic Al–Si alloys

The effect of La2O3 in the Al–P–Ti–TiC–La2O3 modifier on primary silicon has been investigated. The results show that La2O3 in the Al–P–Ti–TiC–La2O3 modifier play an important role in modifying primary silicon. According to the present experiment, when the modifier containing La2O3 was added to Al–20 wt.% Si alloy at 850 °C, La2O3 in the modifier was decomposed (partly or completely). The minimum primary silicon size (approximately average 18 μm) modified with Al–P–Ti–TiC–La2O3 modifier is obtained at the holding time of 30 min, and the primary silicon size hardly change with the increase in holding time from 30 to 90 min. Primary silicon size (approximately average 150 μm) in unmodified Al–20 wt.% Si alloy is about nine times larger than that (approximately average 18 μm) in modified Al–20 wt.% Si alloy with Al–P–Ti–TiC–La2O3 modifier at the holding time of 30 min. As compared with unmodified Al–20 wt.% Si alloy, the Brinell hardness value of modified Al–20 wt.% Si alloy with Al–P–Ti–TiC–La2O3 modifier at the holding time of 30 min is increased by 39%.