Modification Of Eutectic Si Research Articles

Achieving simultaneous improvement in strength and ductility in Al–Si–Mg–Ce alloy through synergistic morphology modification of eutectic (Si) and Al2Si2Ce phases by Sr addition

In this paper, it was found for the first time that with Sr addition in Al–Si–Mg–Ce alloy, the morphology of eutectic (Si) can be modified from branch to fine fibrous, while the bulk-like Al2Si2Ce phase may replace the elongated needle-like one. Moreover, Mg was observed to segregate along the (Al)/Al2Si2Ce interface and Sr was found to concentrate in the interior of Al2Si2Ce phase. Such heterostructured Sr–Al2Si2Ce was also supported by first-principles calculations. The synergistic morphology modification of eutectic (Si) and Al2Si2Ce phases by Sr addition stimulated the simultaneous improvement in strength and ductility in Al–Si–Mg–Ce alloy.

Correlation of Electron Configuration, Electronegativity, and Ionization Energy of Strontium on the Modification of Eutectic Si in High-Pressure Die Cast A380 Al–Si Alloys

Correlation of Electron Configuration, Electronegativity, and Ionization Energy of Strontium on the Modification of Eutectic Si in High-Pressure Die Cast A380 Al–Si Alloys

Effect of solidification pressure on the corrosion behavior and mechanical properties of Al-7Si-3Cu-(0.4 Mg)-(0.5Ge) alloys

Developing practical microstructural solutions that simultaneously enable excellent corrosion resistance and mechanical properties in Al-Si-Cu-based alloys has been increasingly in demand. In this study, we attempt to tailor the microstructural evolution to manipulate the mechanical performance and corrosion resistance of Al-7Si-3Cu-(0.4 Mg)-(0.5Ge) alloys fabricated by GPa-level pressure combined with solution and/or aging treatments. It was found that as the solidification pressure increased, the dendritic growth tendency of the α-Al phase became less pronounced, and the modification of eutectic Si became increasingly significant. Complete solid solution alloys were even achieved under 6 GPa. The corresponding kinetic and thermodynamic mechanisms of pressure-induced microstructural evolution were explored in detail. Upon aging treatment, dense irregular Si precipitates emerged from the supersaturated matrix in Al-7Si-3Cu alloys solidified at 5 GPa and 6 GPa, while denser and finer Si precipitates growing along the 〈100〉Al directions dominated the matrix of Al-7Si-3Cu-0.4 Mg-0.5Ge alloys, which resulted in considerable enhancement of mechanical properties. The electrochemical corrosion behavior was evaluated in the as-cast and heat-treated conditions. The underlying corrosion mechanisms were discussed in terms of pressure, supersaturated solutes and precipitates. These results reveal the feasibility of designing high-strength and corrosion-resistant Al-Si-Cu series alloys via the manipulation of pressure and heat treatment.

Simultaneous refinement of α-Al and modification of Si in Al–Si alloy achieved via the addition of Y and Zr

Due to the Si/Zr-poisoning effect, conventional refiners often yield unsatisfactory results in refining α-Al grains for Al–Si alloys. In this work, the refinement of α-Al grains and the modification of eutectic Si are simultaneously achieved through the combined addition of Y and Zr to A356 alloy. The results indicate that the individual addition of Zr aids in refinement due to the formation of heterogeneous nuclei Al3Zr, while Y alone can refine α-Al grains and modify eutectic Si to a certain extent. When Y and Zr are added together, not only is the size of α-Al grains further refined to 22.1 μm, but the morphology of eutectic Si is also completely transformed into a fibrous structure. The interaction between Zr and Y decreases their solubility in the matrix, enhances heterogeneous nucleation, and induces the formation of a Al8FeMg3Si6YxZry phase enriched at grain boundaries, suppressing the growth of eutectic Si flakes. Compared to the use of Al–Ti–B refiners and Sr modifiers, the alloy with 0.25Zr and 0.3Y additions exhibits more significant grain refinement and Si modification. Furthermore, it facilitates the precipitation of fine Al3(Y, Zr) particles during the T6 heat treatment process, resulting in an optimal ultimate tensile strength (UST) of 289 MPa and an elongation of 9.75%.

Effect of heat treatment on microstructural characteristics and mechanical properties of hypereutectic B390 aluminium alloys modified by phosphorus and bismuth

This study investigated the effects of solution treatment and aging processes on microstructural characteristics and mechanical properties of hypereutectic B390 Al-Si Alloy modified by phosphorus (P) and bismuth (Bi). The morphology evolution of primary Si, eutectic Si, intermetallic compounds, and secondary dendrite arm spacing (SDAS) of both initial and modified alloys were investigated in as-cast and heat-treated conditions. It was found that the combination of 0.1 wt%P and 0.5 wt%Bi in B390 alloy resulted in a remarkable modification and refinement of primary Si, eutectic Si, and SDAS compared to initial specimens in the as-cast condition. After heat treating, the fine lamellar eutectic Si and intermetallic compounds underwent a higher degree of fragmentation and coarsening, appearing as small round particles, leading to a more pronounced formation of a supersaturated solid solution. Additionally, the peak aging time of the B390-P-Bi alloy was only 7 h, 2 h less than the initial specimen. After T6 treatment and addition of both 0.1 wt%P and 0.5 wt%Bi, the B390-P-Bi alloy exhibited a smaller rounded Mg3Bi2 phase at peak aging with a 62.07% size reduction compared to the B390-Bi alloy. The results show that adding P with Bi enhanced hardness, ultimate tensile strength (UTS) and elongation because of refinement of the SDAS, primary Si and eutectic Si. These refinements played a crucial role in increasing tensile strength by more effective strengthening through precipitation and grain size reduction. The B390-P-Bi alloy is a promising choice for applications requiring a balance between strength and ductility.

Tailoring the strength and corrosion resistance of Al-7Si: Eutectic Si modification by Sr and Sc

The effects of different content of Sr and Sc on the microstructure, mechanical properties and corrosion resistance of an Al-7Si alloy were investigated. The presence of Sc in the Sr-modified Al-Si alloy resulted in multiple types of eutectic Si morphologies. The modification of eutectic Si improved the yield strengthen and elongation of Al-7Si alloys, but lead to the increase of boundaries between α-Al and eutectic Si particles, which caused decrease of corrosion resistance and polarization resistance. The incomplete modification offered a possibility to satisfy the require that a compromise between mechanical properties and corrosion resistance. The relationship between the content of Sr and Sc and the morphologies of eutectic Si in the alloy was also summarized.

A new synergy to overcome the strength-ductility trade-off dilemma in Al–Si–Cu alloy by micro-nano-particle complex clusters

The effects of the novel micro-nano-particle clusters (nano-AlN and submicron-TiC particles doped with B, referred as TiCB) on the microstructure and mechanical properties of the Al–9Si–3Cu alloy are investigated herein. Comprehensive analysis revealed that the nano-AlN particles resulted in a significant modification of eutectic Si by causing the poisoning of twin plane re-entrant edge growth of Si and restricting the growth of Si crystals. Correspondingly, the morphology of Si transformed from flaky to fibrous. Furthermore, the synergy of areas with and without particle clusters was emphasized to address their contributions to the simultaneous improvement of the strength and ductility. When inoculating the micro-nano-particle clusters into the Al–9Si–3Cu alloy, the yield strength, ultimate tensile strength, and elongation were 138 MPa, 253 MPa, and 5.8%, respectively, corresponding to increases of 23.2%, 23.4%, and 123.1% compared with those of the uninoculated Al–9Si–3Cu base alloy (112 MPa, 205 MPa, and 2.6%, respectively). After T6 heat treatment, the spheroidal Si and θ′ phases on the Al matrix further improved the strength of the Al–9Si–3Cu alloy. This work may provide a promising strategy to design and fabricate Al–Si–Cu alloy with high strength and ductility.

Effect of Eu and P additions with Ta grain refiner on the solidification microstructure of Al-7Si-0.3Mg alloys

Al-7Si-0.3Mg based alloys have been widely used. Nevertheless, at least three issues during melt treatment (grain refinement of Al grains, modification of eutectic Si and refinement of eutectic grain size) need to be further explored. In this contribution, we focus on these three melt treatments. For grain refinement of Al grains, the stochiometric Al-2.2Ti-1B grain refiner rod together with 0.12 wt. % Ta was used. For modification of eutectic Si, Eu up to 500 ppm was used. The best modification can be obtained with 200 ppm Eu. By further increasing Eu up to 500 ppm, modification level becomes worse due to the formation of Al2Si2Eu. For the refinement of eutectic grain size, a combined addition of Eu (up to 500 ppm) and P (up to 40 ppm) was used. With increasing P concentration, the modification of eutectic Si became worse. The size of eutectic Si increases, the shape factor of eutectic Si decreases. When the P concentration is higher, more Eu is needed for a well-modified eutectic Si. This investigation provides a novel concept for melt treatment of Al-Si-Mg based alloys.

A study on the interaction between a Sr modifier and an Al-5Ti-1B grain refiner in an Al-7Si-0.35Mg casting alloy

A Sr modifier and an Al-Ti-B grain refiner were simultaneously added to an Al-7Si-0.35Mg cast alloy and the interaction between Sr and Al-5Ti-1B was investigated. The combined additions of 100 ppm Sr and 500 ppm Ti produced both eutectic Si modification and α-Al grain refinement while increasing the nucleation frequency of Al-Si eutectic grains compared to an alloy with the addition of Sr alone. TEM analysis revealed that Al2Si2Sr phases existed with either TiB2 or AlP and TiB2 coupling particles. This suggests that pre-existing TiB2 particles in the melt form prolific AlP, the most potent nuclei for Si, and thereby promote the nucleation of the eutectic Al-Si grains during solidification despite the deactivation of AlP consumed for the preceding formation of Al2Si2Sr.

Grain refinement and modification of an Al–Si–Mg–Ti–Be cast alloy: microstructure and tensile property

In this study, the combined use of grain refinement and modification was studied on a hypoeutectic Al–Si–Mg–Ti–Be cast alloy. The primary α-Al grains were transformed from columnar dendrites in the as-received alloy into fine equiaxed dendrites. Meanwhile, the eutectic Si with irregular morphologies were modified to fine fibrous. The room-temperature ultimate tensile strength is increased by ∼14% from 145 MPa to 165 MPa, while the elongation to fracture is increased from 3% to 5%. The comprehensive enhancement of mechanical properties is due to the synergistic effect of microstructural refinement and isotropic improvement by α-Al grain refinement and eutectic Si modification.

Grain refinement and eutectic modification of A356 casting alloy by adding Al-B-Sr master alloys and its effect on tensile properties

The effects of the grain refinement and eutectic Si modification on tensile properties by using Al-B-Sr master alloys in A356 cast alloy were investigated. Two different master alloys, Al-4%B-1%Sr (4B1Sr) and Al-3%B-3%Sr (3B3Sr), were developed. In microstructure observation, the master alloys were consisted of AlB2, SrB6, AlSrF, KAlF4 and Al4Sr compounds. It should be noted that the α-Al phase also exists in two master alloy. The result showed that the AlB2 area fraction in the 4B1Sr alloy was higher than the 3B3Sr alloy. The 4B1Sr alloy has better efficiencies of α-Al grain refinement and eutectic Si modification than the 3B3Sr alloy, and α-Al grains are refined from 3035 to 312 μm and the eutectic Si is modified from the acicular to fibrous morphology. The tensile properties of 4 wt% treated with 4B1Sr alloy has higher UTS and elongation compared to the treated with 3B3Sr alloy.

Modification of eutectic Si in hypoeutectic Al-Si alloy with novel Al-3Ti-4.35La master alloy

Grain refinement and eutectic Si modification of hypoeutectic Al-Si alloys are crucial to improving their mechanical properties. In this paper, the effects of a novel Al-3Ti-4.35La master alloy on the morphology of eutectic Si and mechanical properties of hypoeutectic Al-7Si alloy were studied, and the modification mechanism on eutectic Si was revealed. The results show that the addition of 0.2 wt% Al-3Ti-4.35La master alloy can transform the eutectic Si phase from the coarse plate and needle to fine fiber and partial granular structure. After modification, the ultimate tensile strength and elongation of the Al-7Si alloy reached 178.3 MPa and 12.0%, which are enhanced by 15.6% and 106.9%, respectively, over the unmodified alloy. A detailed analysis revealed that, on one hand, the addition of Al-3Ti-4.35La master alloy can reduce the nucleation temperature of eutectic Si in Al-7Si, shorten the eutectic reaction time, and inhibit its growth. On the other hand, the morphology of eutectic Si can also be affected by altering its growth behavior. The twinning density in the eutectic Si after the modification increases significantly while the growth direction is anisotropic. The modification mechanism of the Al-3Ti-4.35La master alloy on eutectic Si is believed to be consistent with the impurity-induced twinning mechanism (IIT). This work provides important insights into alloy modifications by rare-earth master alloys.

Effect of Ultrasonic-Assisted Modification Treatment on the Microstructure and Properties of A356 Alloy.

Ultrasonic treatment was applied to an A356 aluminum melt with different modifiers, and the effects of ultrasonic treatment on the structure and properties of the A356 alloy were studied. The results showed that α-Al was effectively refined with different ultrasonic modification treatments. In particular, ultrasonic treatment showed the most obvious refinement with macroscopic grains of unmodified alloy and optimized the refinement of secondary dendrite arm spacings in the Sr/Ce synergistic alloys. The eutectic Si of the unmodified A356 alloy had no obvious change after the ultrasonic treatment, but the branch diameter of the eutectic Si reduced in the Sr and Sr/Ce modification alloys after the ultrasonic treatment. The ultrasonic treatment significantly improved the ultimate tensile strength and elongation of the as-cast A356 alloy with the unmodified material, which was due to refinement of the α-Al grains by the ultrasonic treatment. After the T6 heat treatment, the ultimate tensile strength values of the alloys showed no obvious change due to the ultrasonic treatment, but the plasticity of the alloy was significantly improved. Mg2Si precipitation was the dominant strengthening mechanism during the T6 heat treatment, while the plasticity was determined by the size and distribution of the eutectic Si. Acoustic cavitation caused by the ultrasound-activated impurities and the induced heterogeneous nucleation and supercooled nucleation in the groove melt was the main cause of the α-Al refinement, the eutectic Si modification and the improvement in the mechanical properties.

Casting A356+SiCp with ultrasonically treated melts

Low mass fractions (0.05 wt%) of SiC micro sized particles have been added to an A356 melt and dispersed by ultrasonic vibration to study their impact on the microstructural morphology of cast samples. It is shown that the ultrasonic melt treatment at 680°C can promote a homogenized distribution of the reinforcement while also degassing the melt and induces a moderate grain refinement. Even though SiC may act as a nucleant, its use did not induce a significant grain refinement relatively to ultrasonically treated unreinforced melts. Adding SiC microparticles, however, seems to enhance Eutectic Si modification, although it contributes to its slight coarsening at the expense of Mg2Si.

Primary Si refinement and eutectic Si modification in Al-20Si via P-Ce addition

Enhancing the mechanical properties of hypereutectic Al-Si alloys by refining the primary and eutectic Si morphology is very challenging. In this study, the refinement mechanism of primary and eutectic Si morphologies via the simultaneous addition of P-Ce into the Al-20Si alloy was studied. Microstructural analysis revealed that the primary and eutectic Si morphologies were significantly refined, which increased the tensile strength. Furthermore, the addition of Ce, up to 0.6 wt%, can result in the formation of Ce-rich intermetallic phases, which may lead to a significantly increased tensile strength while retaining the ductility of the alloy. The ultimate tensile strength of the Al-20Si alloy increased from 96 to 175 MPa, and the elongation increased from 1.0% to 1.7% with the addition of P-Ce. Moreover, the wear resistance of the alloy improved. The added P and Ce did not react with each other to form an intermetallic compound; therefore, this method can simultaneously refine primary and eutectic Si.

Characterization of in-situ reinforced (Al,Si)3(Ti,Ce) precipitates in T6 treated A356-0.3wt.%Ce-1.5vol.%TiCN composite and its effects on mechanical properties

In the present study, the microstructural evolution and mechanical properties of T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite were studied. The results demonstrated that the grain refinement and eutectic Si modification effects of T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite are remarkable than that of T6 treated A356 alloy, and similar to that of T6 treated A356–0.3wt.%Ce alloy. More importantly, the in-situ reinforced (Al,Si)3(Ti,Ce) precipitates were found in T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite. TEM results and simulated diffraction pattern corresponding to the proposed crystal structure indicated that the (Al,Si)3(Ti,Ce) precipitates could be indexed consistently according to a body-centered tetragonal structure (I4/mmm space group, D022 type) with lattice parameters approximately of a = 0.519 nm and c = 0.859 nm. The existence of (Al,Si)3(Ti,Ce) precipitates resulted in the increase of strength due to the load bearing and coefficient of thermal expansion (CTE) mismatch strengthening. Besides, the fracture mode of the T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite is a transgranular fracture. Compared with the T6 treated A356–0.3wt.%Ce alloys, A356–0.3wt.%Ce-1.5vol.%TiCN alloys showed better elongation, which is ascribed to the transformation of needle-like and hard Ce-rich phases distributing along with the eutectic Si to blocky and relatively soft (Al,Si)3(Ti,Ce) phases. The ultimate tensile strength (UTS) and the elongation (El) of the A356–0.3wt.%Ce-1.5vol.%TiCN composite were increased by 3.7% and 32.7% than that of the A356–0.3wt.%Ce alloy, respectively.

Modification mechanism and tensile property of Al-9Si-0.4Mg-0.1Cu alloy

In this work, eutectic Si modification grade formula was established and effect of Sr element on modification level and mechanical properties of Al-9Si-0.4Mg-0.1Cu alloy was studied. Thermal analysis, SEM, EPMA and TEM were applied to analyze cooling curves, microstructure and Si twinning of the alloys. The results showed that precision and accuracy of eutectic Si modification grade formula were significantly improved and quantitative evaluation modification level of eutectic Si could be achieved. Modification level of eutectic Si increased first and then decreased with Sr content increasing. Though twin plane re-entrant edge (TPRE) mechanism and impurity induced twinning (IIT) mechanism were effective under certain conditions, they cannot fully explain the modification mechanism of eutectic Si in Al-9Si-0.4Mg-0.1Cu alloy. Sr element caused constitutional undercooling at the front of solid-liquid interface, promoted the formation of fine Al 2 Si 2 Sr phases and nano-precipitates, resulting in the changes of size and morphology of eutectic Si. With the improvement of eutectic Si modification level, the UTS and El of the alloys increased. While, adding excessive Sr led to the formation of coarse Al 2 Si 2 Sr, which was detrimental to the improvement of modification level and mechanical properties of alloy. • Modification level function suitable for quantitatively evaluate modification grade of eutectic Si was established. • Fine Al 2 Si 2 Sr phases and nano-precipitates change the size and morphology of eutectic Si. • Coarse Al 2 Si 2 Sr reduces the modification level of eutectic Si and the mechanical properties of alloy.

Effect of addition of 3 %Al2O3 on mechanical and microstructural properties in Al-16Si hypereutectic alloys with pouring temperature

It is well know that the mechanical properties of hypereutectic Al-Si alloys are affected by the size, volume fraction and distribution of primary and eutectic Si particles. However, the pouring temperature of the alloy also acts as the vital role for simultaneous refine and modifying Si particles in hypereutectic Al-Si alloys by conventional means. The particles distribution of nano particles on the melt is different at different pouring temperature which affects the physical, mechanical and the microstructural behavior of Al-Si alloys. Various content of gamma Al2O3 nano particles were added in hypereutectic Al-16Si alloy melt and further dispersed through an ultrasonic cavitation based technique. The cast hypereutectic Al-16Si alloy with the nano particles’ addition showed a significant enhancement in hardness, strengths and ductility. The wear behaviour of the materials depends on the distribution of intermetallic compound over melt. This paper suggests that gamma Al203 nano particles effectively induced simultaneous refinement of primary Si and modification of eutectic Si, resulting in superior ductility enhancement that is much higher than those conventional methods can offer. Moreover, the large plate eutectic Si particles were also modified into fine core particles. The result could have great potential for numerous applications. The experiment has been performed on a group of specimens under different loads and with different speeds. We observe from the experiment that, with the increase in Al2O3 content wearing tendency decreases due to formation of Al-Si intermetallic compounds.

Factors affecting eutectic Si modification in Al-Si hypoeutectic alloy with the addition of Na, Sr, Eu and Yb

Factors affecting eutectic Si modification in Al-Si hypoeutectic alloy with the addition of Na, Sr, Eu and Yb were investigated. The modification effect is determined by element concentration in eutectic Si, which is mainly attributed to the solubility of modifying element M in α-Al and the interaction energy parameter of Al (or Si) and modifying element. A great modification is achieved by M of a limited solubility in α-Al and a moderate interaction energy parameter of Si (or Al) and M. The results are verified by the experimental results reported in the previous literatures. The effect of cooling rate on modification is also discussed in this work.

Effects of thermal-rate treatment and modification of Ce on the microstructure and properties of A356 alloys

In this study, the effects of thermal-rate treatment (TRT) and modification of Ce on the microstructure and mechanical properties of A356 alloy were investigated. The results showed that the microstructure of A356 alloy was improved after TRT and modification of Ce. The α-Al was refined significantly and the eutectic Si transformed from needle-like shape to granular-like shape. When the content of Ce increased to 0.5%, the grain size of α-Al of A356 alloy began to increase and the dendrites became coarse. When the Ce content was 0.4%, the tensile strength and yield strength of A356 alloy were 183MPa and 124 MPa, respectively. The mechanism of (TRT+Ce) on the grain refinement of α-Al and modification of eutectic Si was discussed.