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Abstract: The effect of Al–P–Ti–TiC–Nd2O3 modifier on the microstructure and mechanical properties of hypereutectic Al–20wt.%Si alloy has been investigated. It has been concluded that Nd2O3 in Al–P–Ti–TiC–Nd2O3 modifier can modify primary silicon in hypereutectic Al–Si alloys. Statistical analysis shows that primary silicon size (approximately average 38μm) in modified Al–20wt.%Si alloy with Al–P–Ti–TiC modifier is larger than that (approximately average 20μm) in modified Al–20wt.%Si alloy with Al–P–Ti–TiC–Nd2O3 modifier. Compared with primary silicon modified with Al–P–Ti–TiC modifier, Primary silicon modified with Al–P–Ti–TiC–Nd2O3 modifier has the smaller size at different holding times such as 10, 60 and 120min. The internal defects in coarser primary silicon particles play an important role in determining the tensile strength and elongation of the materials. Coarser primary silicon particles in unmodified Al–Si alloys can degrade the loading bearing capacity of the materials. Modification can eliminate the internal defects to a great extent and improve the tensile strength and elongation of hypereutectic Al–Si alloys. Compared with unmodified and heat-treated Al–20wt.%Si alloy, the tensile strength of the modified with Al–P–Ti–TiC–Nd2O3 modifier and heat-treated Al–20wt.%Si alloy increases by 20%. [Copyright &y& Elsevier]

Abstract: 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–20wt.% Si alloy at 850°C, La2O3 in the modifier was decomposed (partly or completely). The minimum primary silicon size (approximately average 18μm) modified with Al–P–Ti–TiC–La2O3 modifier is obtained at the holding time of 30min, and the primary silicon size hardly change with the increase in holding time from 30 to 90min. Primary silicon size (approximately average 150μm) in unmodified Al–20wt.% Si alloy is about nine times larger than that (approximately average 18μm) in modified Al–20wt.% Si alloy with Al–P–Ti–TiC–La2O3 modifier at the holding time of 30min. As compared with unmodified Al–20wt.% Si alloy, the Brinell hardness value of modified Al–20wt.% Si alloy with Al–P–Ti–TiC–La2O3 modifier at the holding time of 30min is increased by 39%. [Copyright &y& Elsevier]

Abstract: The modification of in situ formed Mg2Si in Mg–Si alloys with yttrium (Y) was investigated. As-cast microstructure analysis of Mg–5wt.% Si alloys indicates that all the primary Mg2Si crystals are surrounded by a layer of α-Mg dendritic halos, which is again surrounded by the eutectic Mg2Si+Mg structures. When the Y content is 0.1 or 0.4wt.%, the sizes of primary and eutectic Mg2Si do not significantly reduce in Mg–5wt.% Si alloys. When the Y content is 0.8wt.%, the mean size of primary Mg2Si decreases from more than 100μm to about 30μm or less; furthermore, the Chinese script type Mg2Si particle also exhibits modified morphology as a fine fiber. When the Y content is further increased to 1.2wt.%, the primary Mg2Si becomes coarser again and even larger than that in the unmodified alloy; however, the eutectic Mg2Si still exhibits modified morphology as a fine size. The size and amount of Mg–Y point compounds are increased with the increasing of Y content in the alloys. In addition to distributing in α-Mg phase, the Mg–Y point compounds are also present in primary Mg2Si dendritic crystal. In the unmodified alloy, the coarse primary Mg2Si is formed by the preferred growth that occurs at the tips of branches; however, when the alloy is modified with 0.8wt.% Y, the preferred growth manner of the primary Mg2Si was depressed, while another type of growth, isotropic growth manner, is enhanced in the modified alloy. [Copyright &y& Elsevier]

Abstract: The modification effect of KBF4 on the primary and eutectic Mg2Si in Mg–Si alloy is better than that of K2TiF6. This may be the reason of the presence of B in melts. However, the modification effect of KBF4 is greatly weakened by the simultaneous addition of K2TiF6 due to the decreasing of B content in the melts by the formation of TiB and TiB2. [Copyright &y& Elsevier]

A method is proposed to estimate quantitatively the shifting distance of the eutectic point in a horizontal direction (under non-equilibrium solidification condition). The shifting distances of the eutectic point in Al–20wt.%Si alloys under the non-equilibrium solidification condition are 0.4 and 0.9wt.% in a horizontal direction towards higher silicon contents with the addition of 0 and 3wt.% master alloys (Al–20wt.%Y2O3), respectively. [Copyright &y& Elsevier]

Abstract: In this study, a new Al–P–Ti–TiC–Y modifier has been successfully designed to modify primary silicon in hypereutectic Al–20wt.%Si and Al–29wt.%Si alloys. The results show that the morphologies of primary silicon crystals are drastically changed from irregular morphologies, such as starlike (fivefold) and coarse platelet to regular morphologies. Statistical analysis shows that primary silicon sizes in modified Al–20wt.%Si and Al–29wt.%Si alloys (approximately 20 and 35 μm, respectively) are smaller than those in unmodified Al–20wt.%Si and Al–29wt.%Si alloys (approximately 100 and 250 μm, respectively). As compared with unmodified Al–20wt.%Si and Al–29wt.%Si alloys, the Brinell hardness values of modified Al–20wt.%Si and Al–29wt.%Si alloys are increased by 15.8% and 32%, respectively. The wear rates of the modified Al–20wt.%Si and Al–29wt.%Si alloys are lower than those of the unmodified Al–20wt.%Si and Al–29wt.%Si alloys (under loads ranging from 3 to 9 N), respectively. [Copyright &y& Elsevier]

Abstract: In the present study, the effect of Nd on primary silicon and eutectic silicon in hypereutectic Al-20wt.%Si alloy has been investigated. It has been concluded that Nd in Al–P–Ti–TiC–Nd modifier can modify not only eutectic silicon but also primary silicon in hypereutectic Al-20wt.%Si alloy. Statistical analysis shows that primary and eutectic silicon crystallite sizes (approximately 60μm and 40μm in length, respectively) in modified Al-20wt.%Si alloy with Al–P–Ti–TiC modifier are about seven- and two-times larger than those (approximately 22μm and 18μm in length, respectively) in modified Al-20wt.%Si alloy with Al–P–Ti–TiC–Nd modifier, respectively. [Copyright &y& Elsevier]