Sr Master Alloy Research Articles

Investigation of Modifying Alloying Elements in High-Pressure Injection Casting Eutectic Al-Si Alloys

In the study, the mechanical properties of aluminum alloys produced by the injection molding method, especially using Strontium and Titanium metals, were optimized without being subjected to cold forming. Mechanical tests were applied to the alloys produced by the high-pressure casting technique, and their strength, hardness, and microstructure were examined. Optical and SEM microscopy examinations investigated grain structures. Within the scope of the study, AlTi5B1 master alloy and AlSr10 master alloy were added to the pure AlSi10 (Fe) alloy in 5 different compositions. AlTi5B1 master alloy added to pure AlSi10(Fe) alloy significantly increased the hardness by reducing the grain size. Si modification took place with the addition of AlSr10 master alloy, and it was observed that the obtained weight ratios of 150ppm, 300ppm, and 450ppm Sr increased the hardness proportionally by 2.5 HB each. With the increase in Ti and Sr master alloys added, a significant increase was observed in tensile and yield strengths and % elongation rates. In the compression test, the percentage (%) deformation elongation, the reduction of the grain structure of the material by the added Ti and Sr elements, and the transformation of the eutectic silicon into a spherical structure absorbed the applied Fm force. This led to an increase in strength, and while the permanent deformation elongation decreased as the weight of Ti increased, it was observed that the permanent deformation elongation decreased proportionally with each added amount of 150 ppm Sr. The addition of the Ti element reduced the grain size by shrinking the α-Al dendrites, but it did not affect the eutectic Si.

Heterogenous Grain Nucleation in Al-Si Alloys: Types of Nucleant Inoculation

The objective of the current work is to establish, on the one hand, the conventional mechanisms of grain refining and, on the other hand, the effect of the refining-modification interaction in Sr-modified Al-Si alloys on the achieved grain refining and the modification of eutectic silicon. For this purpose, the hypereutectic alloy A390.1 (~17%Si) was used. Various grain refiners were used, namely, Al-10%Ti, Al-5%Ti-1%B, and Al-4%B. After the preparation of the liquid metal, several concentrations of these master alloys were added to the liquid bath according to the desired objective. The different melts prepared were heated at 750 °C and cast in a preheated graphite mold with a solidification rate of around 0.8 °C/s. The liquid metal was. The presence of strontium (added in the form of Al-10%Sr master alloy) and boron completely affects the microstructure of the alloy. An atom of Sr unites with 6 atoms of B to form a compound whose stoichiometric formula is of the SrB6 type, leading to a significant reduction in the modification. A strong relationship exists between the addition of B and the recovery level of Sr. The affinity between titanium and boron is stronger than the affinity between boron and strontium. Both B and TiB2 phase particles do not react with Si; it is only the Ti part of the Al-Ti-B master that forms (Al, Si)3Ti. Regardless of the amount of Si content in the alloy, the Al-4%B master alloy achieves the best grain refining compared to Ti-containing master alloys.

Refining and modification effects of (Al, Zr, Si)–Al4Sr on Al–7Si–0.5 Mg alloy

The Al–9Zr-0.9Sr master alloy was used to refine and modify the Al–7Si-0.5 Mg alloy, and to improve the refining and modification effects, the Al–9Zr-0.9Sr master alloy was carried out melt spinning treatment. The second phase particles in the ribbon are smaller and more evenly distributed than those in the ingot. The Al–Zr–Sr inoculation showed excellent refining and modification effects on Al–7Si-0.5 Mg alloy, and in the range of 1 wt.%∼4 wt.%, the refining effect was gradually enhanced with the increase of the inoculant dosage. The morphology and size of particles in inoculant have significant effects on the refinement and modification effects of the inoculant. The X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and selected area electron diffraction (SAED) results showed that in Al–7Si-0.5 Mg matrix alloy, (Al, Zr, Si) instead of Al3Zr was used as the heterogeneous nucleation substrate of α-Al to refine the grains. The Sr element in the master alloy was mainly used to modify eutectic silicon, and melt spinning could effectively improve its modification effect on eutectic silicon. With the increase of inoculant dosage, the mechanical properties of the alloy were gradually improved. However, when the dosage was increased to 4 wt.%, some large rod-like particles appear due to the excessive Zr element, resulting in a decrease in elongation.

Metallothermic Production of Aluminum–Strontium Master Alloy for Modification of Silicon

Strontium master alloy is widely used in today’s aluminum foundries for modification of Al–Si alloys. In this study, Al–Sr master alloy was produced in molten Al alloy directly from strontium carbonate instead of using the pure strontium metal which is difficult to store in the air due to its high oxygen affinity. In a laboratory-scale induction furnace, SrCO3 and SrO powders were injected into the liquid metal via argon flow and subjected to reduction reaction. The oxygen-free medium required for the reduction was provided by the gas purged on both the surface and the inside of the liquid metal. Hence, the master alloy was produced directly by an economical process. Moreover, the addition of Mg to the reducing melt decreased the surface tension of the liquid aluminum; as a result, the reduction efficiency was increased. At the best of the results, the master alloy containing 5.15% Sr was obtained by reducing approximately half of the fed SrO by Al6Mg. This master alloy was used to modify A360 alloy, and the same modification effect as the commercial Al5Sr master alloy was observed.

Mechanical properties, corrosion behavior, and microstructure of Sr modified Al–9.2Mg–0.7Mn alloys

AbstractThe influence of strontium (Sr) additions in the form of Mg–Sr master alloys from 0 to 0.6 wt% on the mechanical properties, corrosive nature, and microstructure of Al–9.2Mg–0.7Mn alloys is investigated. The material is studied in a fully annealed (O‐temper) and a sensitizing treatment at 150°C for 7 days. Here we demonstrate that there will be a new phase which might be (Al, Mg)17Sr2 formed in the as‐cast microstructure. When the Sr content is 0.2 wt%, under the premise that the mechanical properties of completely annealed alloy change little (relative to the matrix: the ultimate tensile strength increases by 8 MPa and the elongation only decrease by 1.6%), the intergranular corrosion resistance is significantly improved. The specific performance is that the mass loss from intergranular corrosion decreases by more than 53% from the addition of 0.2 wt% Sr after sensitizing.

Effect of Al-Sr master alloy on the formation of long period stacking ordered phase and mechanical properties of Mg-Gd-Zn alloy

The rapid formation of profuse fine Long Period Stacking Ordered Structure (LPSO) lamellae is especially desired for Mg-Gd-Zn alloys as type II wherein LPSO phases are difficult to form in as-cast state and prolonged heat treatments are necessary. The aim of this work is to investigate the effect of various Al-10 Sr master alloy additions (0, 0.6, 1.8, in wt. %) on LPSO formation in as-cast Mg-14.02Gd-2.33Zn alloy and the microstructural evolution during subsequent heat treatment and ECAP processing as well as their mechanical behavior variations. Minor addition of 0.6 wt. % Al-Sr master alloy introduces abundant 18R and 14H-LPSO phases in as-cast Mg-Gd-Zn alloy, and accelerates the microstructural evolution into high density of well-aligned long fiber-like 14H nanolamellae only through short-time solid solution and 1-pass ECAP processing as well as low-temperature aging. While a higher level of 1.8 wt. % (Al-Sr) addition produces short rod-like 14H particulates and considerable hard Al2Gd, network (Mg, Al)3Gd intermetallic compounds deteriorating the mechanical property. Consequently, processed Mg-Gd-Zn-0.6(Al-Sr) alloy exhibits a superior mechanical property due to synergistic effects of long fiber-like LPSO phase strengthening and grain refinement strengthening and so on. This paper provides an effective and economical method to fabricate high-performance Mg-Gd-Zn alloys reinforced with LPSO phases.

Effect of cooling rates of production process of Al-3%B-3%Sr master alloy on grain refinement and eutectic modification efficiency in cast A356 alloy

In this paper, size and morphology of the grain refiner and modifier particles in the Al-3%B-3%Sr master alloy production by using different cooling rates were investigated. Two Al-3%B-3%Sr master alloys were produced with 0.2 and 10°C/s, respectively. The grain refinement and eutectic modification efficiency of the Al-3%B-3%Sr master alloy were tested in casting process of A356 alloy by addition of 4wt.% and holding times for 10-120 min. The experimental result showed that microstructure of the M1 alloy (Slow cooling) consisted of larger solidified particles of AlB2, SrB6and Al4Sr in the matrix of α-Al compared to the M2 alloy (Rapid cooling). The addition of the M1 alloy in cast A356 alloy, it was found that small grain size and fully modify eutectic silicon were obtained from the holding time in a range of 10-60 min. While the addition of M2 alloy, a small grain size was achieved in shorter holding time in a range of 10-30 min but the eutectic silicon was partly modify. From the thermal analyzed result, solidification of un-modified A356 alloy was changed after addition of Al-3%B-3%Sr master alloy. It was clearly observed that both the undercooling of nucleation and eutectic reaction was reduced and the solidification time was shifted to longer.

Microstructure evolution of Al–Sr master alloy during continuous extrusion

The microstructure evolution of Al–Sr master alloy during continuous extrusion was investigated using X-ray diffractometer, scanning electron microscope and transmission electron microscope. Results indicate that the continuous extrusion process could change the Al4Sr particles of the alloy significantly in size and morphology. The as-cast needle-like Al4Sr particles are broken into small blocks in upsetting zone and crushed heavily in adhesion zone. Plenty of dislocations get tangled up in right-angle bending zone. Al4Sr particles grow in the extending zone. Finally, Al4Sr particles in products are approximately 28 μm in length. Al2Sr particles precipitate during the process. Compared with products by horizontal extrusion, Al4Sr particles by continuous extrusion are finer and distribute more evenly.

A Metallographic Study of Grain Refining of Sr-Modified 356 Alloy

The grain refining influence of Ti and B in the presence of Sr was investigated in A356.2 alloy using Al–10 wt%Ti, Al–5 wt%Ti–1 wt%B, Al–2.5 wt%Ti–2.5 wt%B, Al–1.7 wt%Ti–1.4 wt%B and A1–4 wt%B master alloys. Strontium modification of the A356.2 alloy was carried out using Al–10 wt%Sr master alloy and two levels of Sr: 30 ppm and 200 ppm. The occurrence of intermetallic phases resulting from Sr–Ti and/or Sr–B interactions was investigated using electron microprobe analysis and metallographic techniques. Addition of B in amounts exceeding 0.1 wt% led to the formation of particles containing predominantly B and Sr, with a composition approaching SrB6. No interaction between Sr and Ti was observed. Thus, the boron content of the alloy should be considered as one of the parameters which would affect successful grain refinement and modification of A356.2 castings. The effect of Sr/B interaction on the grain size of the A356.2 alloy samples is also presented.

Comparation about Refining Efficiency to Microstructure of AZ31 Magnesium Alloy for Sr Master Alloys

In the present work, the influence of Al-Sr and Mg-Sr master alloys on the as-cast microstructure of the AZ31 magnesium alloy was investigated,and the refinement efficiencies of both master alloys were also analyzed and compared. The research results indicate that both the Al-Sr and Mg-Sr master alloys have obvious refinement effect on the as-cast microstructure of the AZ31 magnesium alloy, and the refinement efficiency of the Mg-Sr master alloys was better than that of the Al-Sr master alloys. The mechanisms for the differences of grain refinement efficiency between Al-Sr and Mg-Sr master alloys on the AZ31 magnesium alloys were also discussed.

Modification performance on 4032 Al alloy by using Al–10Sr master alloys manufactured from different processes

The microstructures and modification performance on 4032 aluminum alloy of the Al–10Sr master alloy wire prepared from “direct reaction-hot extrusion” and the trapezoidal block from “direct reaction” were systemically studied by using optical metallurgical microscope, XRD and SEM. It was found that the preparation processes exhibited a significant effect on the microstructures of the Al–10Sr, which thereby influenced its modification performance. It has been found that when the Al–10Sr alloy wire was used, a desirable modification was obtained after 2min and reached to the best performance at 60min, and the optimum Sr addition amount was 0.04–0.06wt%, and the good modification performance was kept even after 300min. However, when the Al–10Sr alloy trapezoidal block was used, a desirable modification was started after 30min and reached to the best performance as long as 120min, and the optimum Sr addition amount was 0.06–0.08wt%, and the effective modification period was only 180min. Therefore, comparing with the Al–10Sr alloy trapezoidal block, the Al–10Sr alloy wire had better modification efficiency, which not only reduced the Sr addition amount of about 30%, but also greatly decreased the incubation time and improved the ability of anti-fading.

Effects of grain refining and modification on mechanical properties and microstructures of Al–7.5Si–4Cu cast alloy

Al–7.5Si–4Cu cast alloy melt modified by Al–5Ti–B, RE and Al–10Sr master alloys were poured in the chromite sand moulds, to investigate comparatively the effects of individual or combined additions of grain refiners and modifiers on the mechanical properties, microstructures, grain refining and modification, and intermetallic compounds of the alloy. The results show that the mechanical properties and the microstructures of Al–7.5Si–4Cu cast alloys are improved immensely by combining addition of 0.8%Al–5Ti–B, 0.1%RE and 0.1%Al–10Sr grain refiners and modifiers compared with the individual addition and cast conditions. For individual addition condition, addition of 0.8% Al–5Ti–B master alloy can obtain superior tensile strength, Brinell hardness and finer equiaxed α(Al) dendrites. The alloy with 0.1% RE master alloy shows the highest improvement in ductility because the rare earth can purify the molten metal and change the shape of intermetallic compounds. While the alloy with 0.1% Al–10Sr modifier shows only good improvement in yield strength, and the improvement of other performance is unsatisfactory. The Al–10Sr modifier has a significant metamorphism for the eutectic silicon, but will make the gas content in the aluminum alloy melt increase to form serious columnar grain structures. The effects of grain refining and modification on mean area and aspect ratio have the same conclusions obtained in the mechanical properties and the microstructures analyses.

On thermal analysis, macrostructure and microstructure of grain refined Al–Si–Mg cast alloys: role of Sr addition

The present study aimed at investigating the influence of grain refinement in combination with Sr modification on the solidification behaviour of A356·2 alloy, and the resulting micro- and macrostructures obtained. Grain refinement of A356·2 alloy using Ti and B additions in the ranges of 0·02–0·5% and 0·01–0·5% respectively was studied using five different grain refiners in the form of Al–10%Ti, Al–5%Ti–1%B, Al–2·5%Ti–2·5%B, Al–1·7%Ti–1·4%%B and Al–4%B aluminium master alloys. Sr modification of the alloys was carried out using Sr additions of 30 and 200 ppm in the form of Al–10%Sr master alloy. The probable interactions between Sr and Ti and Sr and B were investigated using different metallographic techniques. Thermal analysis was also used to evaluate these interactions. Electron microprobe analysis revealed that adding >0·1%B to the A356·2 alloy may lead to formation of particles predominantly containing B and Sr, with a composition approaching SrB6.

Effect of grain refiner on the tensile and impact properties of Al–Si–Mg cast alloys

The present study aims to investigate the influence of the addition of Ti and B in the form of five different grain refiners/aluminium master alloys (Al–10%Ti, Al–5%Ti–1%B, Al–2.5%Ti–2.5%B, Al–1.7%Ti–1.4%B and Al–4%B) in conjunction with that of Sr (as modifier) added in the form of Al–10%Sr master alloy to A356.2 alloy. Grain refinement of an A356.2 alloy with Ti and B additions in the ranges of 0.02–0.5% and 0.01–0.5%, respectively, was examined using these different types of grain refiners. Strontium additions of 30 and 200 ppm were made. All alloys were T6-heat treated before mechanical testing. Tensile and impact tests were conducted to evaluate the influence of the interaction between grain refiner and modifier on the mechanical properties. The properties were determined for both the as-cast and heat-treated conditions.

Probing the local atomic structure of Sr-modified Al–Si alloys

Extended X-ray absorption fine structure (EXAFS) spectroscopy and atom probe tomography (APT) measurements were jointly used for the first time to probe the local structure around Sr atoms in Al–10%Sr master alloy and in Al–3%Si–0.04%Sr and Al–12.5%Si–0.04%Sr eutectic alloys in order to study the impact of trace levels of Sr on the morphological changes occurring in Al–Si binary eutectic alloy. EXAFS analysis shows the oxidation states of Sr is close to Sr0 in all the alloys studied. In the Al–10%Sr master alloy, Sr atoms tend to form the intermetallic compound Al4Sr. On the other hand, in Al–Si alloys, Sr atoms segregate towards Si-rich regions, preferentially bonding to Si atoms to form Al2Si2Sr-like clusters with a coordination environment consistent with bulk Al2Si2Sr. APT study reveals the presence of nanometer-sized Al-rich and Si-rich regions and support the EXAFS results. We speculate that addition of trace levels of Sr to Al–Si binary alloy system results in the initial formation of Al2Si2Sr-like clusters and the presence of such intermetallic clusters could play an important role such as poisoning of nucleation sites, thereby delaying the nucleation of eutectic phases and causing the morphological changes of the eutectic phases in the Al–Si alloys.

Effect of Strontium and T6 Heat Treatment on Structure and Performance of Al-11.6Si-0.5Mg Alloy

In this study, Strontium (Sr) was added as modifier during the casting of Al-11.6Si-0.5Mg alloy, and the effect of T6 heat treatment on microstructure and performance of alloy was also investigated. The results showed that the 0.3% Al-8%Sr master alloy can refine effectively the α-Al dendrite and eutectic structure; the best economic process of T6 heat treatment is solution at 535°C for 6 hrs., and water cooling at 50~60°C,aging at 160°C for 6 hrs , then air cooling. After Sr modification and T6 heat treatment, the mechanical properties of alloy are improved remarkably, i.e., the tensile strength increased to 348MPa from 183MPa before modification and the elongation raises from 3.0% to 6.5%. So this alloy is applied to the strain clamp products in electric power fitting industry.

Modification of Sr on 4004 Aluminum Alloy

As a brazing foil, 4004 Al alloy has good welding performance. However, the high Si content decreases the plasticity of the alloy. To improve the plasticity of 4004 Al alloy and subsequently improve the productivity of 4004 Al foil or 434 composite foil, 4004 Al alloy was modified by Al-10%Sr master alloy. Modification effects of an additional amount of Sr, modification temperature, and holding time on 4004 aluminum alloy were studied by orthogonal design. The results showed that the greatest impact parameter of 4004 aluminum alloy modification was the additional amount of Sr, followed by holding time and modification temperature. The optimum modification parameters obtained by orthogonal design were as follows: Sr addition of 0.04%, holding time of 60 min, and modification temperature of 760°C. The effect of Sr addition on modification was analyzed in detail based on orthogonal results. With increasing of Sr addition, elongation of 4004 alloy increased at first, and decreased after reaching the maximum value.

Effect of P and Sr complex modification on Si phase in hypereutectic Al–30Si alloys

In this paper, the complex modification process of P and Sr for hypereutectic Al–30Si alloys was investigated. After the addition of 2.0% Al–3P and 0.7% Al–10Sr master alloys continuously added during the melt inoculation and solidification process, the primary Si can be significantly refined from more than 200.0μm decreasing to 32.8μm with homogeneous distribution and eutectic Si was obviously modified as fibrous simultaneously. The modification mechanism was also studied. It is found that the melt temperature has influence in the interaction between P and Sr. At about 1000°C, AlP is surrounded by Al4Sr phase to form encapsulation structure, which would react with Sr to form Sr3P2 at approximate 1300°C. However, P and Sr take the respective form of AlP and Al4Sr at 770°C, which just be the reason for the excellent complex modification of Si phase using continuous refining method.

Mg–Zr–Sr alloys as biodegradable implant materials

Novel Mg–Zr–Sr alloys have recently been developed for use as biodegradable implant materials. The Mg–Zr–Sr alloys were prepared by diluting Mg–Zr and Mg–Sr master alloys with pure Mg. The impact of Zr and Sr on the mechanical and biological properties has been thoroughly examined. The microstructures and mechanical properties of the alloys were characterized using optical microscopy, X-ray diffraction and compressive tests. The corrosion resistance was evaluated by electrochemical analysis and hydrogen evolution measurement. The in vitro biocompatibility was assessed using osteoblast-like SaOS2 cells and MTS and haemolysis tests. In vivo bone formation and biodegradability were studied in a rabbit model. The results indicated that both Zr and Sr are excellent candidates for Mg alloying elements in manufacturing biodegradable Mg alloy implants. Zr addition refined the grain size, improved the ductility, smoothed the grain boundaries and enhanced the corrosion resistance of Mg alloys. Sr addition led to an increase in compressive strength, better in vitro biocompatibility, and significantly higher bone formation in vivo. This study demonstrated that Mg–xZr–ySr alloys with x and y ⩽5wt.% would make excellent biodegradable implant materials for load-bearing applications.

Morphology modification of Mg 2Si by Sr addition in Mg-4%Si alloy

A modification of Mg 2Si in the hypereutectic Mg-4%Si alloy (mass fraction) with Sr was investigated. Two types of Mg 2Si in the alloys were found: polygonal primary Mg 2Si and Chinese script type eutectic Mg 2Si. Adding Al-10% Sr master alloy to the Mg-4%Si alloy clearly reduced the average size of primary Mg 2Si and changed the morphology of eutectic Mg 2Si from Chinese script type to polyhedral or fine fibre shape. The refinement of primary Mg 2Si is mainly attributed to the heterogeneous nucleation mechanism induced by the Sr-rich particles. The modification of eutectic Mg 2Si results from the dissolved Sr, which alters the preferred growth manner of the eutectic.