Effect of phosphor addition on eutectic solidification and microstructure of an Al-13％Si alloy

As the refiner or modifier, the master alloys containing high concentration phosphor are widely used in preparing eutectic or hypereutectic Al-Si alloys. To study the effect of phosphor addition on the eutectic solidification and microstructure of the Al-13%Si alloy, an investigation has been undertaken by means of thermal analysis and micro/macro-structure observation. Results indicate that addition of phosphor in near eutectic Al-Si alloy promotes the nucleation of eutectic but has little refinement impact on primary Si particles as expected. Conversely, both primary Si particles and eutectic Si flakes become slightly coarser in P-rich alloys. The coarsening of eutectic Si flakes ties closely to the increased eutectic growth temperature with phosphor addition. The eutectic solidification of the alloy proceeds from the near mold zone towards the center, and it is also found that a few independent nucleation regions emerge in liquid at the solidification front due to the addition of phosphor.     

Microstructure and mechanical properties of hypereutectic Al-Si alloy modified with Cu-P

The microstructure and mechanical properties of Al-14.6Si castings modified by Cu-P master alloy under different conditions were studied with optical microscope（OM） and mechanical testing and simulation（MTS）.The results indicate that the Cu-P master alloy possesses not only obvious modification effect,but also longevity effect with more than 8 h on the hypereutectic Al-Si alloy.It is shown from thermal calculation,scanning electron microscope（SEM）,and energy dispersive analysis of X-rays（EDAX） that the modification mechanism of Cu-P on primary silicon in the castings is heterogeneous nucleation around AlP particles.The Cu-P master alloy has no or little modifying effect on eutectic silicon,even though it has obvious modification on primary silicon in the castings.This may be because of the fast transformation of eutectic silicon at a very narrow temperature,which will notably weaken the role of AlP particles as heterogeneous nuclei for eutectic silicon.     

An Al-12Si/ZnS powder inoculant for eutectic silicon in Al-12Si alloy

To obtain high-performance Al-Si-based cast alloys,refinement and modification of Si phases are required.An Al-12Si/ZnS powder inoculant was designed and fabricated using a chemical bath deposition method.The efficiency of the inoculant for modifying the eutectic Si phase in as-cast Al-12Si alloy was studied.Results show that Al-12Si/ZnS powder can significantly refine the eutectic Si in Al-Si cast alloys.The best refinement effect for eutectic Si is achieved with 17.5wt.%Al-12Si/ZnS powder.Coarse long needle-shaped eutectic Si with a length of 18μm was modified into approximately spherical shape with a diameter of 6.53μm,which is evenly distributed throughout the alloy.The E2EM model calculation indicates that the inter-plane misfit(F_p)and inter-atomic spacing misfit(F_r)between ZnS and Si are all less than 0.5%,which confirms that ZnS is a potential nucleation site for Si phase.The hardness,tensile strength,and elongation of Al-12Si alloys modified with 17.5%Al-12Si/ZnS powder increase 6.30%,16.18%and 55.45%,respectively,compared to the unmodified Al-12Si alloy.The fracture behavior of the alloy with 17.5wt.%Al-12Si/ZnS powder is dominated by transgranular fracture supplemented by intergranular fracture.     

United modification of Al-24Si alloy by Al-P and Al-Ti-C master alloys

The modification effect of a new type of Al-P master alloy on Al-24Si alloys was investigated.It is found that excellent modification effect can be obtained by the addition of this new type of Al-P master alloy into Al-24Si melt and the average primary Si grain size is decreased below 47μm from original 225μm.It is also found that the TiC particles in the melt coming from A18Ti2C can improve the modification ffect of the Al-P master alloy.When the content of TiC particles in the Al-24Si melt is 0.03%.the improvement reaches the maximum and keeps steady with increasing content of TiC particles.Modification effect occurs at 50 min after addition of the Al-P master alloy and TiC particles,and keeps stable with prolonging holding time.     

Refinement of primary Si in Cu–50Si alloys with novel Al–Zr–P master alloy

In this article, a novel Al-6Zr-2P master alloy with ZrP particles was successfully synthesized, and the refining performance of this novel master alloy for the primary Si in Cu-50Si alloys was also investigated. By means of the fracture plane observation, it is found that the ZrP phase would precipitate first in the solidification process, and then, the ZrAl 3 phase grows around them. Furthermore, it is observed that the refining effect can be remarkably improved by changing the addition sequence of the raw materials. After the melting of commercial Cu, the 2.0 wt% Al-6Zr-2P master alloy and crystalline Si were added in sequence, and the mean size of the primary Si in Cu-50Si alloy can be significantly refined from 255.7 to 75.3 lm. Meanwhile, the refining mechanism was discussed in detail.     

Effect of Bi modification treatment on microstructure,tensile properties,and fracture behavior of cast Al-Mg2Si metal matrix composite

Bi has a good modification effect on the hypoeutectic Al-Si alloy,and the morphology of eutectic Si changes from coarse acicular to fine fibrous.Based on the similarity between Mg2Si and Si phases in crystalline structure and crystallization process,the present study investigated the effects of different concentrations of Bi on the microstructure,tensile properties,and fracture behavior of cast Al-15wt.%Mg2Si in-situ metal matrix composite.The results show that the addition of the proper amount of Bi has a significant modification effect on both primary and eutectic Mg2Si in the Al-15wt.%Mg2Si composite.With an increase in Bi content from 0 to 1wt.%,the morphology of the primary Mg2Si is changed from irregular or dendritic to polyhedral shape;and its average particle size is significantly decreased from 70 to 6 μm.Moreover,the morphology of the eutectic Mg2Si phase is altered from flake-like to very short fibrous or dot-like.When the Bi addition exceeds 4.0wt.%,the primary Mg2Si becomes coarse again.However,the eutectic Mg2Si still exhibits the modified morphology.Tensile tests reveal that the Bi addition can improve the tensile strength and ductility of the material.Compared with those of the unmodified composite,the ultimate tensile strength and percentage elongation after fracture with 1.0wt.% Bi increase 51.2% and 100%,respectively.At the same time,the Bi addition changes the fracture behavior from brittle to ductile.     

Effect of phosphorus and heat treatment on microstructure of Al-25%Si alloy

It is known that phosphorus can refine the primary silicon and heat treatment can spheroidize the eutectic silicon. This paper presents an optimal combination of heat treatment processes and P refinement on hypereutectic Al-Si alloy. The optimal P addition amount, and the solution and aging temperatures for Al-25%Si alloy were obtained through the orthogonal experiment, and their modification effects were discussed. The results show that P addition has the greatest modification effect, followed by aging temperature, and the modification effect of solution temperature is the least. The optimized modification parameters are: addition of 0.6% P, solution at 540 oC and aging at 160 oC . In addition, the cooling curve, superheating and hardness of the alloy were also analyzed.     

Modification and aging precipitation behavior of hypereutectic M-21wt.%Si alloy treated by P＋Ce combination

In the present study, the tested hypereutectic Al-21wt.%Si alloys were prepared by modifying the melt using different proportions of P and Ce, and then applying T6 heat treatment. The modification effects and mechanism of P＋Ce complex modifier on the Si phase of hypereutectic Al-21wt.%Si alloy were studied, and the aging precipitation behavior after modification was characterized by means of tensile strength measurement, OM, SEM and TEM analysis. The results show that the massive primary silicon phase particles are significantly refined after modification, while the needle-like eutectic silicon crystals become fibrous and short. It was found that the mechanism of phosphorus modification on the primary silicon can be attributed to heterogeneous nucleation of AlP, while the modification mechanism of Ce can be explained by adsorbing-twinning theory. In the aged microstructure of the modified hypereutectic Al-21wt.%Si alloy, there existed some strengthening phases such as AI4Cu9, Al2Cu, AlCu3, and Al57Mn12. The P＋Ce complex modifier not only affected the size of primary silicon and eutectic silicon, but also the aging behavior of alloys under the heat treatment process. When Al-21wt.%Si alloy was modified using 0.08%wt.P ＋ 0.6wt.% Ce, the aging precipitates were dispersed uniformly in the alloy, and its mechanical properties at room and elevated temperatures are optimized （Rm = 287.6 MPa at RT, Rm = 210 MPa at 300 ℃）.     

Effects of cooling rate and B content on microstructure of near-eutectic Al-13wt%Si Alloy

Under cooling rates of 2 ℃/s and 10℃/s, the influences of B content on the microstructure of near eutectic Al-13.0wt%Si alloy have been investigated. Results showed that the addition of boron resulted in refinement of eutectic grains, and to some extent, had an inhibiting effect on precipitation of the primary phases, and the refining and inhibiting effects are much more obvious at higher cooling rate. When B was not added, higher cooling rate promoted the α-Al dendrites formation. At lower cooling rate, the addition of B did not cause the so called ＂columnar to equiaxed transition （CET）＂, however, at higher cooling rate, this transition was obvious. After the addition of B, the nucleation temperature TN ascended and nucleation mode changed from nucleation mode of from wall towards centre （without B addition） to a nucleation mode that the eutectic nucleated evenly throughout whole sample （with B added）. It can be concluded that the addition of B offers a large amount of nuclei for eutectic solidification, as a result, the eutectic grains was refined. Higher cooling rate will lead to more nuclei, so the effects on the refinement of eutectic grains and on suppression of primary phases are increased.     

Effects of P＋Cr complex modification and solidification conditions on microstructure of hypereutectic AI-S alloys by wedge-shaped copper mould casting

Large and segregated primary Si particles may drastically decrease the mechanical properties of AI-Si alloys. To solve this problem, a P-Cr complex modifier was added into the alloy, and the effects of P-Cr complex modification and solidification conditions on the microstructure of hypereutectic Al-Si alloys casting produced in wedge-shaped copper mould were studied. The thermal analysis technique was applied to calculate the cooling rate during solidification. The microstructures were observed by means of optical and scanning electron microscopies. Results showed that the primary Si segregates in the as-cast hypereutectic AI-Si alloys. The segregation of primary Si can be inhibited by adding a P＋Cr complex modifier and increasing the cooling rate during solidification. The refinement of primary Si particles by P＋Cr complex modification is due to the formation of CrSi2 and AlP particles which act as the heterogeneous nuclei for the primary Si phase. The segregation of Si was also inhibited through the adherence of heavier CrSi2 particles to the primary Si particles.     

Effects of Al-Mn-Ti-P-Cu master alloy on microstructure and properties of Al-25Si alloy

To obtain a higher microstructural refining efficiency, and improve the properties and processing ability of hypereutectic AI-25Si alloy, a new environmentally friendly AI-20.6Mn-12Ti-0.9P-6.1Cu （by wt.%） master alloy was fabricated; and its modification and strengthening mechanisms on the AI-25Si alloy were studied. The mechanical properties of the unmodified, modified and heat treated alloys were investigated. Results show that the optimal addition amount of the AI-20.6Mn-12Ti-0.9P-6.1Cu master alloy is 4wt.%. In this case, primary Si and eutectic Si as well as e-AI phase were clearly refined, and this refining effect shows an excellent long residual action as it can be heat-retained for at least 5 h. After being T6 heat treated, the morphology of primary and eutectic Si in the AI-25Si alloys with the addition of 4wt.% AI-20.6Mn-12Ti- 0.9P-6.1Cu alloy changes into particles and short rods. The average grain size of the primary and eutectic Si decreases from 250 IJm （unmodified） to 13.83 pm and 35 IJm （unmodified） to 7 tim; the e-Al becomes obviously finer and the distribution of Si phases tends to be uniform and dispersed. Meanwhile, the tensile properties are improved obviously; the tensile strengths at room temperature and 300 ℃ reach 241 MPa and 127 MPa, increased by 153.7% and 67.1%, respectively. In addition, the tensile fracture mechanism changes from brittle fracture for the alloy without modification to ductile fracture after modification. Modifying the morphology of Si phase and strengthening the matrix can effectively block the initiation and propagation of cracks, thus improving the strength of the hypereutectic AI-25Si alloy.     

Effect of alumina short fiber and air-cooling processing on solidification microstructure and tensile properties of Al2O3/Al-15Si composites

The effect of microstructure variation by addition of alumina short fiber and optimization of tensile properties by air-cooling processing in Al2O3/Al-15Si composites were studied.The results show that in Al-015Si alloy matrix composites with 14% and 30%(volume fraction)fiber,the primary silicon is hardly refined,but the eutectic silicon is effectively refined and granulated.Granulation of some eutectic silicon mainly happens in fiber segregation areas.Refining and granulation of the eutectic silicon are related to the physical constraint arising from the fiber,After the 30%Al2O3/Al-15Si composite was remelted and air-cooled,the number of the eutectic silicon on the surface of the fiber increases,which results in the improvement of fiber/matrix interface and tensile properties for the as-cast composite,Air-cooling processing may be reliable for the optmization of the microstructure and properties of fiber reinforced hypereutectic Al-15Si alloy composites.     

Grain refinement of hypoeutectic Al-Si alloy prepared with ELTA by Al-4B master alloy

Electrolytic low-titanium aluminum （ELTA） was produced by adding TiO2 powder to an industrial aluminum electrolyzer. The grain refining effect of Al-4B master alloy in the hypoeutectic Al-Si alloy prepared by using ELTA was investigated, and compared with those of Al-STi, Al-STi-IB and Al-4B master alloys in the similar alloy prepared by using pure Al. The results indicate that when Al-4B is added to the melt of the alloy prepared by using ELTA in terms of the Ti/B mass ratio of S：l, the grain refining effect is better than those ofAl-STi, Al-STi-IB and Al-4B master alloys. Thus, using Al-4B to refine the grain of Al-Si alloys prepared by using ELTA will possibly become a feasible way of obtaining Al-Si alloy with homogeneous and fine microstructure.     

Effect of Ca addition on solidification microstructure of hypoeutectic Al-Si casting alloys

The effect of Ca addition on the solidification microstructure of hypoeutectic Al-Si casting alloys was investigated using scanning electron microscopy(SEM) and differential scanning calorimetry(DSC) methods with particular attention focused on the change of morphologies of primary α-Al and eutectic silicon. Meanwhile,solute distribution in solid-liquid was simulated according to Scheil-Gulliver law. Results showed that primary α-Al and eutectic silicon were refined as Ca content increased because of the variation of the solute concentration in liquid. The addition of Ca increased the nucleation sites like Al_3Ti or Al_2 Cu to promote the nucleation of primary α-Al. Affected by modification effect of Ca,the shape of eutectic silicon changed from flake to fibrous structure. In addition,coarse plate Ca-rich phases could be found along the grain boundary with high Ca content.     

Microstructure and mechanical properties of Al-10Si alloy modified with Al-5Ti

The microstructure, fracture morphology and mechanical properties of Al-10 Si alloy modified with Al-5 Ti were analyzed and tested by optical microscopy, scanning electron microscopy, and universal electronic testing machine. Compared with unmodified Al-10 Si alloy, the area fraction of α-Al phase in Al-10 Si alloy modified at 740 °C increased first and then decreased with the increase of added amounts of Al-5 Ti, and reached the maximum when the added amount of Al-5 Ti was 0.5 wt.%. When the modification temperature increased from 700 to 740 °C with Al-5 Ti being fixed at 0.5 wt.%, α-Al dendrites were refined obviously and the area fraction remarkably increased. Compared with unmodified Al-10 Si alloy, the ultimate tensile strength and elongation of the alloy modified at 740 °C with 0.5 wt.% Al-5 Ti increased by 9% and 49%, respectively. The fracture surface of modified alloy predominantly exhibited ductile fracture.     

Solidification behaviour of Al-7 %Si-Mg casting alloys

The effects of Mg content and cooling rate on the solidification behaviour of Al-7% Si-Mg(mass fraction)casting alloys have been investigated using differential scanning calorimetry, differential thermal analysis and microscopy. The Mg contents were selected as respectively 0.00%, 0.35% and 0. 70% (mass fraction). DTA curves of Al-7%Si-0.55%Mg(mass fraction) alloy at various cooling rates were accomplished and the alloy melt was cast in different cooling rates. The results indicate that increasing Mg content can lower the liquidus and binary Al-Si eutectic transformation temperatures. Large Fe-rich π-phases (AlsFeMg3Si6) are found in the 0.70% Mg alloys together with some small β-phases (Al5FeSi) ; in contrast, only β-phases are observed in the 0.35% Mg alloys. The test results of the Al-7%Si-0.55% Mg alloys identify that the liquidus and binary Al-Si eutectic transformation temperatures decrease, and the quantity of ternary Al-Si-Mg2 Si eutectic phase decreases as the cooling rate increases.     

Influence of Ca on microstructure and corrosion resistance of Mg-14Li alloy

In order to improve the corrosion resistance of magnesium lithium alloy, Mg-14 Li alloy with different content of Ca(0, 3, 5, 10 wt.%) was prepared with a induction melting furnace. Electrochemical test and corrosion test were carried out in NaCl solution with different Cl~-concentrations. The results indicate that the microstructure of the Mg-14 Li alloy with Ca consists of dendritic β phase and eutectic structure(β+CaMg_2). With the increase of Ca addition from 0, to 3, 5, 10 wt.%, the corrosion resistance of the Mg-14 Li alloy initially increases first and then decreases, and that of alloy with 3% Ca is the best. Therefore, the corrosion resistance of Mg-14 Li alloy in NaCl solution can be effectively improved by adding proper amount of Ca. In addition, the concentration of Cl~-was one of important factors affecting the corrosion resistance of the Mg-14 Li alloy, and the influence of Ca was slighter than that of Cl~-.     

Preparation of casting alloy ZL101 with coarse aluminum-silicon alloy

The coarse Al-Si alloy produced by carbothermal reduction of aluminous ore contains 55% Al, 25% Si and some impurities. The main impurities are slag and iron. The process of manufacturing casting Al-Si alloy ZL101 with the coarse Al-Si alloy was studied. The phase constitution and microstructure of the coarse Al-Si alloy, slag and ZL101 were examined by X-ray diffractometry and scanning electron microscopy. The results show that the content of silicon and iron in the casting alloy reduces with the increase of the dosage of purificant and manganese, but increases with the rise of filtering temperature. It is found that casting Al-Si alloy conforming to industrial standard can be produced after refining by using purificant, and removing iron by using manganese and added magnesium.     

Microstructure of interaction interface between Al-Si, Zn-Al alloys and Al2O3p／6061Al composite

Interaction behaviors between Al-Si, Zn-Al alloys and Al2O3p/6061Al composite at different heating temperatures were investigated. It is found that Al2O3p/6061Al composite can be wetted well by AlSi-1, AlSi-4 and Zn-Al alloys and an interaction layer forms between the alloy and composite during interaction. Little Al-Si alloys remain on the surface when they fully wet the composite and Si element in Al-Si alloy diffuses into composite entirely and assembles in the composite near the interface of Al-Si alloy/composite to form a Si-rich zone. The mierostrueture in interaction layer with Si penetration is still dense. Much more residual Zn-Al alloy exists on the surface of composite when it wets the composite, and porosities appear at the interface of Zn-Al alloy/composite. The penetration of elements Zn, Cu of Zn-Al alloy into composite leads to the generation of shrinkage cavities in the interaction layer and makes the microstructure of Al2O3p/6061Al composite loose.