AlP Particles Research Articles

Mechanism of AlP modifying the morphology of Si in Al-20Si alloys based on experimental studies and first-principles calculations

ABSTRACT The modifying influence of aluminium phosphide to the morphology of primary Si and eutectic Si was investigated in hypereutectic Al-20Si alloys via adding Al-Cu-P master alloy (0.5, 1, 20 wt.%). Microstructural results showed when Al-Cu-P addition from 0 to 0.5%, primary Si phase decreases and eutectic Si phase size remains invariable; when addition higher than 0.5%, primary Si phase keeps invariable, eutectic Si phase size increases. To prove the nucleation effect of AlP on Si phase, interfacial properties of Si/AlP interface were investigated using first-principles calculations. Results showed the AlP(100)/Si(100) interface energy is between −1.45 J/m2 and −1.38 J/m2 for Al-terminated and P-terminated AlP model, both is much smaller than liquid Si/crystalline Si interface (0.34 J/m2), consolidates that AlP particles possess strong nucleation potency for Si phases. Therefore, the modifying influence of AlP to the morphology Si phase is well clarified as a function of AlP content in Al-20Si alloys.

The combined effect of rapid solidification and phosphor addition on the microstructure of hypereutectic A390 alloys

The influence of the combined effect of rapid solidification and phosphor addition on the morphology of primary silicon particles in A390 Al-Si alloy has been investigated by using light optical microscope (LOM). The P as modifier element was added in the shape of copper phosphor (Cu3P) master alloy. The results show that as the solidification rate increases, the size of primary silicon particles in A390 alloy reduces and the morphology of these particles evolve from plate-like to the fine nodular shape. The rapid solidification has a significant improvement on the refining performance of P to modify and refine the primary Si particles in A390 alloy. It is suggested that the refining performance of P in Cu3P master alloy is related to the formation the AlP particles which act as a heterogeneous nucleation. This affects the solidification rate and restricts the Si phase's growth.

Effect of Si and P Content on the Si Phase and Solidification Behavior of Al-40Zn-xSi Alloys Using Synchrotron Radiation Real-Time Imaging

In this paper, the effect of Si (1, 3, 5, 6 wt.%) and P (5, 10, 15, 20, 30 ppm) content on the Si phase and solidification behavior of Al-40Zn-xSi alloys are investigated via phase diagram calculation, scanning electron microscopy (SEM) and synchrotron radiation real-time imaging. It is found that Si content has a great influence on the microstructures of Al-40Zn-xSi alloys, and two distinct primary phases were separated by a critical composition at 5.49 wt.% Si in the calculated phase diagram. The microstructure contained not only needle-like eutectic Si, but also blocky primary Si particles in “hypoeutectic” commercial-purity Al-40Zn-5Si alloys. However, the synchrotron radiation real-time imaging experiment showed that the primary phase was α-Al in commercial-purity Al-40Zn-5Si alloys. The effect of P on the Si phase of the high-purity Al-40Zn-5Si alloy was also studied, showing that the number and size of the blocky primary Si particles in the high-purity “hypoeutectic” Al-40Zn-5Si alloys were mainly related to the P impurity content. A small minority of primary Si particles were found during the whole solidification process of the high-purity Al-40Zn-5Si alloy without P impurities, while a large number of primary Si particles were precipitated continuously at the front of α-Al dendrites in the high-purity Al-40Zn-5Si alloy with the addition of 20ppm P, which may have been caused by the fact that AlP particles can act as the heterogeneous nucleation sites of primary Si particles by a small undercooling in P-impurity-containing alloys.

Duplex Nucleation and Its Effect on the Grain Size and Properties of Near Eutectic Al-Si Alloys

Duplex nucleation and its effect on the grain size and properties of near eutectic Al-Si alloys were investigated in this work. It is found that the grain size of Al-13Si-1Cu alloy can be greatly refined by addition of Al-2Ti-0.5B-0.5C and Al-P master alloys, and TiB2/AlP duplex nucleation was observed at the nuclei of primary silicon in the process of studying the refinement mechanism. TiB2 phase coated by Al co-existed with AlP in the nuclei of primary Si. The existence of Al phase should not only guarantee the promotion of TiB2 particles on the nucleation of AlP particles, but also made TiB2 particle stable in the core of primary silicon through the interaction with the Si phase. Duplex nucleation can not only affect the grain size of Al-Si alloy, but also effect of the distribution of strengthening phases in Al-Si alloy and improve the properties. Compared with single Al-P master alloy treatment, the tensile strength of Al-12Si-4Cu-2Ni-1Mg alloy after duplex nucleation treatment are improved obviously. The fatigue performance of Al-12Si-4Cu-2Ni-1Mg alloy is also improved significantly by the duplex nucleation.

Effect of ultrasonic and different modification treatments on the microstructure of cast Al-Si-Cu-Mg-Ni alloy

ABSTRACT The Al-Si-Cu-Mg-Ni alloy is a commonly used piston alloy. In this work, different amounts of phosphorus modifier and Al-2P (Al-2%P) master alloy modifier were added to the original alloy. The ultrasonic melt treatment method was also applied to improved the microstructure of near-eutectic multi-cast Al–Si alloys. Investigation was performed by means of optical microscopy and scanning electron microscopy. The results show that the effect of Al-2P master alloy modifier is more stable. However, the phosphorus modifier requires a higher amount of addition to achieve a refinement effect similar to that of the Al-2P modifier. The external ultrasonic field mainly acts on the AlP particle. The heterogeneous nucleation of the primary Si phase and the AlP clusters formed by the phosphorus modifier are more aggregated than the fine-dispersed AlP particles formed by the Al-2P master alloy modifier in the melt. Hence the ultrasonic melt treatment is more effective for the phosphorus modification.

Hierarchical refinement of primary phases in a multicomponent Al-14Si-CuNiMg casting alloy by ultrasonic melt treatment

The combined effects of ultrasonic melt treatment (UST) with the cooling rate on the microstructural evolution in a multicomponent Al-14Si-CuNiMg casting alloy was investigated. UST was applied to a melt at 800°C, followed by casting into a steel step mold at cooling rates in the range of 4-32 K/s. UST in the fully liquid state significantly reduced the sizes of the primary phases (the phases formed before Al) crystallized in the initial stage of solidification, and the structural refinement by UST became more pronounced for a faster cooling. With trace additions of Ti, V and Zr, the primary phase is most likely (Al,Si)3(Zr,Ni,Fe), and primary Si and then Al3Ni are sequentially formed upon solidification. AlP particles, well-known nucleants for primary Si, were also found to exist inside the (Al,Si)3(Zr,Ni,Fe) and Al3Ni which exhibited a very low lattice misfit with AlP (~0.7 and 4.7%, respectively). This importantly suggests that AlP can nucleate all the primary phases while it has the highest efficiency of structural refinement by UST for (Al,Si)3(Zr,Ni,Fe) phase that first nucleated in the molten metal. The nucleation of the primary phases was quantified using an analytical model based on exponential statistics. The hierarchical refinement operated by UST is further discussed.

Formation mechanism and conditions of fine primary silicon being uniformly distributed on single αAl matrix in Al-Si alloys

In this study, solidification microstructure of fine primary silicon being uniformly distributed on single αAl matrix was obtained when adding Cu–9 wt%P alloy to an Al–10 wt%Si alloy melt or an Al–20 wt%Si alloy melt, stirring at 200 r/min for 12 min and cooling at the cooling rate of 16.3 K·s−1. The change law of silicon phase size with cooling rate and modified treatment parameters was determined by examining the solidification microstructures. It was found that ultrafine AlP was easily swallowed by primary silicon when the cooling rate was slow. The formation mechanism of superfine AlP particles, the growth process of αAl phase around primary silicon and the disappearance process of eutectic silicon were researched under intense stirring of the melt during the Cu–9 wt%P alloy modification. Moreover, the conditions under which fine primary silicon was uniformly distributed in single αAl matrix in hypereutectic Al-Si alloy were put forwarded. Finally, the formation mechanism of the solidification microstructure without eutectic Si in hypereutectic Al-Si alloy was analyzed.

A new Zr-rich intermetallic phase in an Al-14Si-3Cu-4.5Ni casting alloy with trace additions of Zr

A trace addition of Zr to a multicomponent Al-14Si-3Cu-4.5Ni casting alloy has often been found to form a coarse plate-like Zr-rich intermetallic compound with a size of a few tens of μm at the beginning of solidification. Evaluation of the phase composition has confirmed that the Zr-rich intermetallic phase consists of multicomponent constituent elements, mainly Al, Si, Ni and Fe, and is present in a form of (Al,Si)3(Zr,Ni,Fe). The existence of such a complex (Al,Si)3(Zr,Ni,Fe) phase has not yet been predicted by phase equilibria calculation of the multicomponent Al-14Si-CuNiMg systems. In this paper, transmission electron microscopy studies combined with electron backscattered diffraction pattern analysis reveals the crystallography information of the (Al,Si)3(Zr,Ni,Fe) phase for the first time and identifies it as a modified Al3Zr-D023 crystal (tetragonal, I4/mmm(139)) with slightly changed lattice parameters of a = b = 3.275 Å and c = 15.475 Å. The primary (Al,Si)3(Zr,Ni,Fe) phase is found to nucleate directly onto AlP particles. The mechanical properties of the Zr-rich intermetallics were also investigated using nanoindentation at both room and elevated temperatures and were compared to those of the Si phase.

Reactive synthesis of hexagonal Ti5P3.16 crystals and their heterogenous nucleating mechanism on primary Si

Reactive synthesis of Ti5P3.16 crystals was firstly investigated in the Al–Ti–P–C alloy and their effective refinement on primary Si in Al–Si alloys was also revealed. It was found that the Ti5P3.16 phase was formed by the direct reaction of P atoms with TiC particles in Al melt. During the reaction process, P atoms absorbed on TiC agglomerates and initiated the gradual phase decomposition, and then the releasing Ti atoms combined surrounding P ones together to form Ti-P phase. Based on the TEM and SEM characterization, it is identified that the Ti5P3.16 phase has an hexagonal close packed crystal lattice structure and mainly displays a regular hexagonal prism morphology enclosed by six {10-10} facets and two parallel {0001} ones. Furthermore, the Al–Ti–P–C alloy containing the Ti5P3.16 particles showed an efficient refinement performance on primary Si particles for hypereutectic Al–Si alloy, whose average size was reduced from 85 μm to 12.5 μm for A390 alloy. In order to reveal the refinement mechanism, the evolution process of the Ti5P3.16 phase induced by Si atoms in the Al–Si melt was carried out, indicating that the Ti5P3.16 transformed into amounts of nano AlP particles with sizes of about 100–200 nm after added into the melt. Then, these in-situ AlP particles with fresh interfaces distributed uniformly in the melt and act as the effective heterogenous nuclei for the primary Si during the following solidification process of Al–Si melt with the decrease of the melt temperature, which leads to significantly refinement of the microstructure of A390 alloys.

Interaction of Ca, P trace elements and Sr modification in AlSi5Cu1Mg alloys

Thermal and microscopy analyses were carried out to investigate the interaction of Sr modification with Ca and P trace elements in high-purity and commercial-purity Al–5Si–1Cu–Mg alloys. The results show how the addition of Sr to commercial-purity alloy induces significant changes in the nucleation and growth temperatures of eutectic Si since pre-eutectic Al2Si2(CaSr) intermetallics tend to poison AlP particles, making them inactive as nucleation sites for eutectic Si. In contrast, the addition of Sr to high-purity alloy shows no apparent influence on the characteristic temperatures of Al–Si eutectic reaction, even though the microstructural investigations reveal flake-to-fibrous transition in the eutectic Si structure. This indicates that the eutectic growth temperature, commonly used to predict eutectic modification level, is not a key feature of Sr modification, but it is indirectly caused due to the presence of additional impurities in commercial-purity alloys which affect the nucleation kinetics of eutectic Si.

Role of scandium additions in primary silicon refinement of hypereutectic Al–20Si alloys

ABSTRACT This study investigates the effect of Sc on the formation of primary silicon during the solidification of hypereutectic Al–20Si alloys. The evolution of the microstructure was studied using thermal analysis. The results show that the addition of 0·2 and 0·4 wt-% Sc suppresses the nucleation of primary silicon due to the formation of ScP particles instead of AlP particles. For large Sc additions, at the centre of the samples, the primary silicon has a star-shaped morphology with thin branches. The addition of Sc decreases the P refinement efficiency in hypereutectic Al–20Si alloys, which may be a result of the formation of a ScP phase. The results suggest that the addition of Sc poisons the nucleant particles of the primary and eutectic silicon.

Investigation on AlP as the heterogeneous nucleus of Mg2Si in Al–Mg2Si alloys by experimental observation and first-principles calculation

Abstract The microstructural evolution of primary Mg2Si in Al–20%Mg2Si with Al–3%P master alloy was observed by scanning electron microscope. And the interfacial properties of AlP/Mg2Si interface were investigated using first-principles calculations. The calculation results show that AlP(1 0 0)/Mg2Si(2 1 1) and AlP(3 3 1)/Mg2Si(1 1 0) interfaces can form steadily. P-terminated AlP(1 0 0)/Mg2Si(2 1 1) interface with the largest work of adhesion (4.13 J/m2) is theoretically the most stable. The interfacial electronic structure reveals that there are covalent Si–Al, Si–P and Mg–P bonds existing between AlP and Mg2Si slabs. Due to the AlP particles as effective heterogeneous nucleus of Mg2Si, primary Mg2Si particles change from dendrite to octahedron/truncated octahedron, and their sizes decrease to ∼20 μm.

Synergistic effect of ultrasonic melt treatment and fast cooling on the refinement of primary Si in a hypereutectic Al–Si alloy

A mechanism describing the synergistic effect of ultrasonic melt treatment (UST) and subsequent fast cooling on the refinement of primary Si particles in a hypereutectic Al−Si alloy was investigated by examining inoculant particles via high-resolution transmission electron microscopy, serial sectioning, and melt filtration. The application of UST activated non-wetting MgAl2O4 particles with diameters of ∼0.5 μm to nucleate the primary Si phase. The cavitation-enhanced wetting of MgAl2O4 particles caused the formation of the AlP phase at the MgAl2O4 interface, further improving the nucleation potential. The cavitation-enhanced wetting and dispersion of inclusions (such as MgAl2O4) also resulted in the refinement and de-agglomeration of AlP particles. The UST-induced changes to the inoculant particles ultimately increased their number density, and the observed effects became more pronounced after increasing the degree of undercooling up to 20 K, leading to enhanced refinement of primary Si particles at higher cooling rates (up to 102 K s−1).

Microstructural evolution and mechanical properties of Al-7Si-0.3Mg alloys with erbium additions

The mechanical properties of hypoeutectic Al-Si foundry alloys are generally controlled by their microstructures. The present study was performed to determine the influence of erbium (Er) in Al-7Si-0.3Mg alloys on the microstructures and mechanical properties. The evolution of microstructure was studied by thermal analysis and interrupted solidification technique. Optical microscopy, scanning electron microscope, and energy-dispersive X-ray were employed to characterize the alloy microstructures. The results demonstrated that the addition of Er significantly refined both the secondary dendrite arm spacing (SDAS) and the primary α-Al grain. Simultaneously, Er modified eutectic Si phase from coarse acicular plate-like structures into fine fibrous features. We observed that Er additions strongly suppress the nucleation of eutectic Si due to the preferential formation of ErP instead of AlP. Er additions change the eutectic growth mode from nucleation and growth on AlP particles to the propagation of a defined eutectic front from the mold walls. Moreover, Er addition that was cast for different holding times indicated that there was no fading effect on the SDAS, primary α-Al grain size, and eutectic Si morphology. Importantly, the tensile properties of the Er-modified alloys at as-cast and T6 conditions can be enhanced due to simultaneous refinement both the SDAS and the α-Al grains and modification of the eutectic Si.

Promoted nucleation of potent substrates assisted with Al-10Si-2Fe master alloy in Al-Si alloys

Cluster-assisted crystallization induced by Al-10Si-2Fe master alloy was investigated in Al-Si melts assisted with exogenous nucleation substrates. Al-Si-Fe master alloy can enhance nucleation immensely with the existence of AlP in high purity alloys and TiB2·AlP particles in commercial purity Al-Si alloys. TiB2 particles themselves in high purity alloys cannot cooperate with Al-10Si-2Fe master alloy and leave the alloys deep undercooling. In addition, swells on silicon surfaces provide the evidence of pre-nucleation clusters attachment during silicon crystallization. Conclusively, Al-10Si-2Fe master alloy can only function with abundant nucleation substrates and make more of them effective by alerting the crystallization of the Al-Si melts.

The interaction between Eu and P in high purity Al-7Si alloys

The interaction between Eu and P in high purity Al-7Si alloys was investigated. Interrupted solidification experiments were undertaken to study macrostructure evaluation and thermal analyses were performed to obtain characteristic temperatures of the eutectic reaction. Without the presence of Eu, increasing P concentrations results in a significant increase in the number of eutectic grains due to the formation of AlP particles, which can act as nucleation sites for eutectic Si. With the presence of Eu, a decrease in nucleation frequency and thereby an increase in eutectic grain size was observed in alloys containing 5 and 30ppm P due to the interaction between Eu and P, which can be further supported by the results of μ-XRD patterns and SADP of TEM. It was found that most P-rich particles were covered by Eu-rich intermetallics, which are indexed to be Al2Si2Eu phase, indicating that the formation of the pre-eutectic Al2Si2Eu phase may lead to a depletion of pre-existing AlP particles or residual P in the melt. This investigation highlights the effect of the interaction between Eu and P on the nucleation of eutectic Si and eutectic grains.

Revealing heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys.

The heterogeneous nucleation of primary Si and eutectic Si can be attributed to the presence of AlP. Although P, in the form of AlP particles, is usually observed in the centre of primary Si, there is still a lack of detailed investigations on the distribution of P within primary Si and eutectic Si in hypereutectic Al-Si alloys at the atomic scale. Here, we report an atomic-scale experimental investigation on the distribution of P in hypereutectic Al-Si alloys. P, in the form of AlP particles, was observed in the centre of primary Si. However, no significant amount of P was detected within primary Si, eutectic Si and the Al matrix. Instead, P was observed at the interface between the Al matrix and eutectic Si, strongly indicating that P, in the form of AlP particles (or AlP ‘patch’ dependent on the P concentration), may have nucleated on the surface of the Al matrix and thereby enhanced the heterogeneous nucleation of eutectic Si. The present investigation reveals some novel insights into heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys and can be used to further develop heterogeneous nucleation mechanisms based on adsorption.

Heterogeneous nucleation of entrained eutectic Si in high purity melt spun Al-Si alloys investigated by entrained droplet technique and DSC

Entrained droplet technique and DSC analyses were employed to investigate the influence of trace elements of Sr, Eu and P on the heterogeneous nucleation of entrained eutectic Si in high purity melt spun Al-5wt.% Si alloys. Sr and Eu addition was found to exert negative effects on the nucleation process, while an increased undercooling was observed. This can be attributed to the formation of phosphide compounds having a lower free energy and hence may preferentially form compared to AlP. Only a trace P addition was found to have a profound effect on the nucleation process. The nucleation kinetics is discussed on the basis of the classical nucleation theory and the free growth model, respectively. The estimated AlP patch size was found to be sufficient for the free growth of Si to occur within the droplets, which strongly indicates that the nucleation of Si on an AlP patch or AlP particle is a limiting step for free growth. The maximum nucleation site density within one droplet is directly related to the size distribution of AlP particles or AlP patches for Si nucleation, but is independent of the cooling rates. Although the nucleation conditions were optimized in entrained droplet experiments, the observed mechanisms are also valid at moderate cooling conditions, such as in shape casting.

Validated thermodynamic prediction of AlP and eutectic (Si) solidification sequence in Al-Si cast alloys

The eutectic microstructure in hypoeutectic Al-Si cast alloys is strongly influenced by AlP particles which are potent nuclei for the eutectic (Si) phase. The solidification sequence of AlP and (Si) phases is, thus, crucial for the nucleation of eutectic silicon with marked impact on its morphology. This study presents this interdependence between Si- and P-compositions, relevant for Al-Si cast alloys, on the solidification sequence of AlP and (Si). These data are predicted from a series of thermodynamic calculations. The predictions are based on a self-consistent thermodynamic description of the Al-Si-P ternary alloy system developed recently. They are validated by independent experimental studies on microstructure and undercooling in hypoeutectic Al-Si alloys. A constrained Scheil solidification simulation technique is applied to predict the undercooling under clean heterogeneous nucleation conditions, validated by dedicated experimental observations on entrained droplets. These specific undercooling values may be very large and their quantitative dependence on Si and P content of the Al alloy is presented.

Simultaneously refining eutectic grain and modifying eutectic Si in Al-10Si-0.3Mg alloys by Sr and CrB2 additions

The addition of CrB2 and Sr into Al-10Si-0.3 Mg (wt.%)-based alloys not only modify the eutectic Si, but also refine the eutectic grains. CrB2 particles were found to nucleate the eutectic grains, despite the AlP particles being partly removed or depleted by the interaction between Sr and AlP. Furthermore, P level was found to be one of the dominant factors that affect the nucleation of eutectic grains. CrB2 addition with a low P level results in a refined eutectic grain size, despite less AlP particles being present to nucleate the eutectic grains. Porosity was found to be mainly located at the boundaries of eutectic grains, highlighting the importance of the refinement of eutectic grains to reduce the size and optimise the distribution of porosity. This investigation demonstrates a novel approach to refine eutectic grains and modify eutectic Si simultaneously into Al-10Si-0.3 Mg (wt.%)-based alloys, and thereby suggests possible industrial applications.