Sr Master Alloy Research Articles

Fourier Thermal Analysis of Eutectic Al-Si Alloy with Different Sr Content

AbstractThe purpose of this work is to explore the capability of Fourier Thermal Analysis (FTA) to detect differences in solidification kinetics between unmodified and Sr modified eutectic Al-Si alloy obtained from the same base alloy. Experimental melts are produced in silicon carbide crucibles using an electrical resistance furnace and burdens of A356 alloy and commercial purity Si. The addition of strontium to the melts is accomplished using Al-10 pct Sr master alloy rod. Chemical composition is controlled using spark emission spectrometry. The changes in microstructure are characterized using optical microscopy. Thermal analysis are performed in cylindrical stainless steel cups coated with a thin layer of boron nitride, using two type-K thermocouples connected to a data acquisition system. Experimental cooling curves are numerically processed using FTA. Results show changes in solidification kinetics of eutectic Al-Si alloy with different Sr content. These changes, measured at the beginning and during solidification of the probes, can be related to the changes in nucleation and growth causing the differences detected during microstructural characterization of the probes.

Effects of Different Cooling Rate and Modifiers on the Microstructures of 4Y32 Aluminum Alloy

This paper discussed the effects of different cooling rate on the microstructure of the 4Y32 aluminum alloy and the refinement and modification on 4Y32 aluminum alloy by using Na and Al-10%Sr master alloys in various treatment states. And also the effect of Al-10Sr and Al-3Ti-1B compound modification on microstructures of 4Y32 aluminum alloy has also been studied. The results showed that: the primary silicon was eliminated during slow cooling. As the cooling rate increased, the number of primary silicon was also growing, but the size of primary silicon and eutectic silicon were significantly refined; when without modification, the shape of eutectic silicon was needle and flake; 4Y32 aluminum alloy could be effectively refined after Na modification, under the optimum addition amount of 0.8wt%. The best modification was achieved with 15 minutes, that is, the shape of primary silicon changed to small granular or oval and the primary silicon was eliminated; the as-cast structure has been improved after Al-10Sr modification, under the optimum addition amount of 0.2wt. %, the shape of eutectic silicon changed to fine short rod or point and the primary silicon was eliminated; However, in the compound modification, efficiency of Sr was decreased with the increasing additional amount of AI-3Ti-1B master alloy, which was attribute to the interaction of Sr and Ti.

Preparation of Al–Ti–C–Sr master alloys and their refining efficiency on A356 alloy

Al–Ti–C–Sr master alloys with various amounts of Sr were prepared through a method of liquid solidification reactions. The as-prepared Al–Ti–C–Sr master alloys were then used as grain refiners to modify A356 alloy. The microstructures of the Al–5Ti–0.25C–2Sr, Al–5Ti–0.25C–8Sr alloys and modified A356 alloy were investigated. The results showed that the Al–5Ti–0.25C–2Sr alloy consisted of phases of α-Al, lath-shaped or tiny blocky TiAl 3, granular TiC, and blocky or rim AlTiSr, while the Al–5Ti–0.25C–8Sr alloy contained an irregular blocky Al 4Sr phase besides the above-mentioned phases. Satisfactory grain refining and modifying effects were obtained by the addition of Al–Ti–C–Sr alloys (0.5 wt.%) to the A356 alloy. Meanwhile, the sizes of the α-Al dendrites / SDAS(40 µm) decreased to 32.7 µm (or 30 µm).The morphology of eutectic silicon was changed from needle-/platelike form to fibrous/globular form. The grain refinement and modification effects of Al–Ti–C–Sr alloys on A356 alloys were mutually promoted. Compared with the Al–5Ti–0.25C–2Sr alloy, the Al–5Ti–0.25C–8Sr alloy possessed higher efficiency in grain refinement and modification of the A356 alloys.

Effect of grain refinement and modification on the dry sliding wear behaviour of eutectic Al–Si alloys

The present study deals with an investigation of dry sliding wear behaviour of grain refined and or modified eutectic (Al–12Si) Al–Si alloy by using a Pin-On-Disc machine. The indigenously developed Al–1Ti–3B and Al–10Sr master alloys were used as grain refiner and modifier for the grain refinement of α-Al dendrites and modification of eutectic Si, respectively. Various parameters have been studied such as alloy composition, sliding speed, sliding distance and normal pressure. The cast alloys, master alloys and worn surfaces were characterized by SEM/EDX microanalysis. Results suggest that, the wear resistance of eutectic Al–Si alloys increases with the addition of grain refiner (Al–1Ti–3B) and or modifier (Al–10Sr). Further, the worn surface studies show that adhesive wear was observed in Al–12Si alloy in the absence of grain refiner and modifier. However, an abrasive and oxidative wear was observed when the grain refiner and modifier are added to the same alloy. Commercially available LM-6 (12.5%Si) alloy was used for comparison.

Effect of Mg–10Sr master alloy on grain refinement of AZ31 magnesium alloy

The effect of Mg–10Sr master alloy on the grain refinement of AZ31 magnesium alloy is investigated. The results indicate that the various Mg–10Sr master alloys (original, rolled, aged and remelted) can effectively refine the grains of AZ31 alloy. Furthermore, for a given 60-min melt holding time, the average grain size of AZ31 alloy treated with the various Mg–10Sr master alloys gradually decreases with the Sr amount increasing from 0.01 to 0.1%. In addition, for a given Mg–10Sr master alloy and 0.1% Sr, the average grain size of the AZ31 alloy treated for 20-min melt holding time is larger than that of the AZ31 alloy treated for 40, 60 or 80 min, and the effect of melt holding time on the average grain size becomes unobvious after 20 min. The grain refinement of AZ31 alloy treated with the various Mg–10Sr master alloys may be explained by the GRF (growth restriction factor) mechanism.

Comparation about efficiency of Al–10Sr and Mg–10Sr master alloys to grain refinement of AZ31 magnesium alloy

In the article, the effects of Al–10Sr and Mg–10Sr master alloys on the grain refinement of AZ31 magnesium alloy, are compared and analyzed. The results indicate that adding Al–10Sr or Mg–10Sr master alloys to AZ31 magnesium alloy could effectively reduce its grain size, but the refinement efficiency of Mg–10Sr master alloys is higher than that of the Al–10Sr master alloys. In addition, for a given melt holding time, the refinement efficiency of the two master alloys respectively increase with Sr adding amount increasing from 0 to 0.1 wt%, and the increasing laws are similar. For a given Sr adding amount, the refinement efficiency of Al–10Sr mater alloy gradually increases with the melt holding time increasing from 20 to 80 min, but its changing is not obvious for the Mg–10Sr mater alloy. The difference of refinement efficiency for the Al–10Sr and Mg–10Sr master alloys might be related to the dissolution modes and rates of Al4Sr and Mg17Sr2 phases in the melt of AZ31 magnesium alloy.

Effects of solutionized Al–10Sr master alloys on grain refinement of AZ31 magnesium alloy

In the paper, the effects of solutionized Al–10Sr master alloys on grain refinement of AZ31 magnesium alloy are investigated. The results indicate that the effects of solid solution treatment on the morphology and size of Al 4 Sr phases in the commercial Al–10Sr master alloy are obvious. With the solutionized temperature increasing from 400 °C to 600 °C, the size of Al 4 Sr phases reduces gradually, and the morphology of Al 4 Sr phases evolves from coarse block shape to fine block and flake shapes. Comparing with the commercial Al–10Sr master alloy, the solutionized Al–10Sr master alloys exhibit higher refinement efficiency to AZ31 magnesium alloy, and the refinement efficiency increases with the solutionized temperature increasing from 400 °C to 600 °C. The mechanism might be related to the dissolution rates of Al 4 Sr phases in the melt of AZ31 magnesium alloy.

Effects of Al-Sr Master Alloys on the As-Cast Microstructure of the AZ31 Magnesium Alloys

The influence of Al-10.5%Sr master alloy, which is much cheaper than Mg-Sr master alloys, on the as-cast microstructure of the AZ31 alloy was investigated. The research results revealed that the Al-10.5%Sr master alloy produced obvious modification of the as-cast microstructure of the AZ31 alloy, and the modification efficiency increased with the holding time from 0min to 60min and the amount of Sr from 0.01% to 0.1%. Moreover, the results also showed that the Al-10.5%Sr master alloys of different states had different modification efficiency on the as-cast microstructure of the AZ31 alloy. The Al-10.5%Sr master alloys in extrusion deformation state and rapid solidification state had better modification efficiency than the Al-10.5%Sr master alloys received and in heat treatment state, which could be related to the microstructure of the Al-10.5%Sr master alloys with different states.

Assessment of modification and formation of intermetallic compounds in aluminum alloy using thermal analysis

In this research, melt of aluminum alloy was modified using Al–10 wt.%Sr masteralloy. Thermal analysis has been used to record the cooling curve of temperature–time for a sample of solidified alloy. Important solidification events have been evaluated using the first derivative-cooling curves. Effect of strontium on the formation temperature and undercooling temperature of intermetallic compounds during pre- and post-eutectic reactions of the alloy has also been investigated using thermal analysis and SEM–EDS. Six reactions in the formation of different phases have been identified by studying first derivative-cooling curves of the alloy. Nucleation temperatures of these phases were studied and compared in both modified and un-modified aluminum alloy.

Microstructural and wear behavior of hypoeutectic Al–Si alloy (LM25) grain refined and modified with Al–Ti–C–Sr master alloy

Present article reports the microstructure and wear behavior of grain refined and modified Al–7Si–0.3Mg (LM25) alloy. Combined grain refinement and modification is achieved by inoculating LM25 melt with various inoculation levels (0.2, 0.5 and 1.0 wt%) of a novel Al base master alloy containing Ti, C and Sr (synthesized in the authors’ laboratory) at 720 °C. The wear resistance of LM25 alloy improves with the addition of this master alloy up to 0.5 wt%. It is observed that α-Al cell size and morphology of the eutectic silicon of LM25 alloy have significant effect on the wear resistance of the alloy.

Effect of grain refining and Sr modification on Prefil measurement sensitivity in 356 alloys using electron probe microanalysis technique

To obtain the best possible Ai–Si alloy casting, the quality of the molten alloy must be optimised, i.e. the molten metal must be free of inclusions, impurities and dissolved gases during the casting process. The cleanliness of the molten metal can be monitored by means of various filtration techniques such as the Prefil (pressure filtration) technique used in the present study. Two melt treatment processes also generally applied to Al–Si alloys to improve the cast microstructure and alloy properties are grain refining and modification. However, the addition of grain refiners (in the form of Al–Ti–B master alloys) or modifiers (in the form of Al–Sr master alloys) to the melt can affect the behaviour of the inclusion measurement system. The present work was carried out on A356 alloys to study the effect of such additions when using the Prefil technique (additions of Ti, B or Sr can skew the Prefil filtration curve and make it less effective). The Prefil experiments were carried out using two types of ceramic filters: standard permeability (SP) filters with an average filter pore size of ~90 μm, and high permeability (HP) filters with an average filter pore size of ~130 μm. The results show that the Prefil curves obtained from the high permeability filters are more sensitive to the presence of oxides (film or particles) than the standard filters. The filtration rate is greatly affected by the amount of grain refiner added. Best results are obtained for the alloy without grain refiner addition. The filtration rate progressively decreases with increasing amount of grain refiner. When the total amount of boron added to the melt (through the Al–5Ti–1B grain refiner used) reaches 60 ppm, the filtration rate is approximately nil. In the case of strontium modification, a reasonably good correlation between the amount of Sr in the molten metal and the Prefil curve (or 'footprint') has been established. However, more experiments are still needed for a better understanding of the effect. Oxidation of Sr is possible, even for concentrations as low as 30 ppm. The SrO oxide particles (white, round shaped) are always seen to be associated with Al2O3 oxide particles (observed in the form of dark short rods). The curvature of the Prefil footprint is found to be sensitive to the amount of oxides present.

Combined effect and its mechanism of Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr master alloy on microstructures of Al–Si–Cu alloy

The combined effect of Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr on Al–Si–Cu alloy has been investigated. Equiaxed dendritic grain of 100–120 μm was obtained with holding time of at least 240 min through addition of more than 0.020% Ti and 0.026% B, though the laminar morphology of eutectic Si kept unaltered. Eutectic Si was completely modified for more than 240 min through addition of Al–10wt.%Sr which also had some benefit on the refinement of primary α-Al. The combined addition of both Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr led to shorter working time of modification and slightly coarser grain size. The above results are mainly due to the formation of SrB 6 through the reaction between Al–10wt.%Sr and Al–3wt.%Ti–4wt.%B. It was found that satisfactory grain refinement and modification could be attained by suitable addition of both Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr in spite of the formation of SrB 6.

Microstructures and modification performance of melt-spun Al-10 Sr alloy

The microstructures of Al-10 Sr alloy quenched at various wheel speeds have been investigated using X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The experimental results show that the microstructures of melt-spun Al-10 Sr alloy are quite different from those of ingot-like alloy consisting of coarse plate-like Al4Sr embedded in the eutectic matrix. For lower wheel speeds of 500 and 1000 rpm, the microstructure is composed of nanoscale particle-like Al4Sr embedded in α-Al solid solution. With wheel speeds exceeding 1500 rpm, the formation of primary Al4Sr phase is completely suppressed and the eutectic microstructure consisting of alternate dark and bright zones is obtained. Eutectic Al4Sr in dark zones is stripe-like and irregular blocky, while regular stripe-like in bright zones, about 10–20 nm in width. Furthermore, modification tests indicate that the modification performance of melt-spun Al-10 Sr alloy is much better than that of ingot-like alloy, reducing the amount of Sr addition and greatly shortening the incubation time. The reasons for the formation of microstructures and the improvement of modification performance of melt-spun Al-10 Sr master alloy have also been discussed.

Recent developments in hypoeutectic Al-Si A-S4G alloy

The effect of adding Sr in the form of the Al-5 Sr master alloy to commercial A-S4G and high purity Al-4Si alloys on the modification process has been investigated. The volume fraction of the eutectic matrix decreased by modification due to the movement of the eutectic point to the higher Si content side. The tensile properties, especially elongation, have been increased by modification. The elongation of the A-S4G alloy is increased from a value of 0.9 to 15% by modification. Additionally, the elongation of the modified high purity alloy reached a value of 34%. The fracture path of the modified alloys circumvents the α-phase while it is not yet known if it propagates intergranularly or transgranularly through the eutectic matrix. The fracture surface revealed dimple and smooth ripple patterns reflecting the high ductility of the modified alloys.

Structural modification of Al-Si eutectic alloy by Sr and its effect on tensile and fracture characteristics

Modification of the commercial A-S13 alloy and high purity Al-Si eutectic alloy has been successfully achieved using Al-5 Sr master alloy. The refined structure showed more fine and uniformly distributed eutectic silicon in the high purity alloy. The incidence of Al-dendrites due to modification was related to the movement of the eutectic point to the higher-silicon side. The chill-cast alloys showed better refined structure and higher mechanical properties in comparison with the sand-cast alloys. The modified chill-cast alloy exhibited the best mechanical properties. The ultimate. tensile strength of which reached 280 M Pa and the elongation was 9.2%. The fracture patterns changed from well faceted brittle appearance to smooth silky and dimple-like for the normal and modified alloys respectively. This reflects the change from brittle to ductile behaviour after modification. A model for the fracture mechanism was proposed to explain the observed higher ductility for the modified alloy.

Dissolution of Non-Reactive Strontium Containing Master Alloys in Liquid Aluminum and A356 Melts

The dissolution behaviour of Al-10%Sr, Al-14%Si-10%Sr and Al-45%Sr master alloys has been investigated in both pure liquid aluminum and in an A356 foundry alloy. These strontium containing alloys exhibit simple dissolution in both types of melts. Both the dissolution rate and the recovery increase with temperature. Over the temperature interval of 675–775°C dissolution was determined to be mass-transfer controlled with associated activation energies of 10–20 kcal/mol. Experimental rate constants for dissolution yielded good agreement with a mass transfer correlation expressed as KM = (0.673(GrM · Sc)0.25 + 0.435 h/r)D/h at 675°C and 725°C;and at 775°C, with KM = (0.60(GrM · Sc)0.26)D/h.

Dissolution of Non-Reactive Strontium Containing Master Alloys in Liquid Aluminum and A356 Melts

The dissolution behaviour of Al-10%Sr, Al-14%Si-10%Sr and Al-45%Sr master alloys has been investigated in both pure liquid aluminum and in an A356 foundry alloy. These strontium containing alloys e...

Microstructure and mechanical properties of modified and non-modified stir-cast Al-Si hypoeutectic alloys

The microstructure and mechanical properties of modified and non-modified stir-cast commercial aluminium alloys A-S7G03 and A-S4G have been investigated. Stir casting of these alloys resulted in spherical and/or rosette shape primary α-phase, and the eutectic silicon was broken into miniature needle morphology. This stir-cast structure slightly improved the mechanical properties in comparison to those of conventionally cast alloys, however the fracture of the stir-cast alloys revealed intergranular brittle fracture. The addition of 0.02% strontium, in the form of Al-5 mass% Sr master alloy, during stir casting modified the eutectic silicon into a very fine spheroidal morphology, while the α-phase particle showed the same morphology as the stir-cast alloys. This novel structure resulted in significant improvement of mechanical properties. The elongation of the modified stir-cast alloys was five times greater than that of the non-modified one. A transgranular mode of fracture was observed for the modified stircast alloys, moreover smooth ripple and dimple patterns were observed reflecting the high ductility of the modified stir-cast alloys.

Structure, mechanical properties and fracture of aluminium alloy A-356 modified with Al-5Sr master alloy

The cooling rate during solidification of the aluminium-silicon alloy A-356 was found to have a pronounced effect not only on the structure and mechanical properties, but also on the modification process using Al-5 mass% Sr master alloy. Cooling rates in the range of 0.2 to 5 K sec−1 were conducted using different types of moulds. Decreasing the cooling rate increases the degree of modification obtained, and a cooling rate of 0.2 K sec−1 showed the optimum modification in the present study. The mechanical properties were significantly improved by modification. Ductility of the modified alloy was eight times greater than that for the non-modified one. Moreover, the mechanical properties of the modified alloys, in the present study, were higher than those modified with sodium, and additionally the ductility of the present modified alloy was higher than that for alloys modified with strontium. A tendency towards ductile rupture was observed. The transgranular type of fracture was optically detected, and a dimple-pattern was observed on the fracture surface by scanning electron microscopy.