Strontium Modification Research Articles

Relationship Between Machinability, Microstructure, and Mechanical Properties of Al-7Si Alloy

Abstract In this work, commercially available Al-7Si alloy was used, and the microstructure was modified by the additions of AlSr15, AlTi5B1, and Al3B. Cylindrical samples were cast into a sand mold and the machinability of the alloys was characterized by means of surface roughness, chip morphology, and buildup edge of the chips. Tool life and surface finish can be improved by decreased chip size by lowering the energy required for machining. The surface finish is an indicator of the quality of the material during the machining process. Therefore, in addition, melt quality was measured by means of reduced pressure test and the calculation of the bifilm index was used to compare the melt quality with machinability. It was found that there is a good correlation between bifilm index and surface roughness of the machined parts. Thus, for a better surface finish, melt quality, which can be quantified by bifilm index, has to be high. AlSr15 modified alloy exhibits the lowest built-up edge with the lowest surface roughness, because strontium modification causes coarse silicon crystals to transform to fine fibrous structure, which enhances machinability.

Quality of the Seam in Welding under Flux by Means of Barium–Strontium Carbonatite

The use of barium–strontium carbonatite in the modification and refining of ferrocarbon alloys is considered. Its use in welding fluxes is proposed. That possibility is analyzed for the example of BSK-2 barium–strontium modifier (Technical Specifications TU 1717-001-75073896–2005) produced by OOO NPK Metalltekhnoprom, with the following composition: 13.0–19.0% BaO, 3.5–7.5% SrO, 17.5–25.5% CaO, 19.8–29.8% SiO2, 0.7–1.1% MgO, 2.5–3.5% K2O, 1.0–2.0% Na2O, 1.5–6.5% Fe2O3, 0–0.4% MnO, 1.9–3.9% Al2O3, 0.7–1.1% TiO2, and 16.0–20.0% CO2. A production technology is proposed for a flux additive containing 70% barium–strontium carbonatite and 30% liquid glass. Several welding-flux compositions based on slag from silicomanganese production are tested. The flux additive is introduced in quantities of 1, 3, and 5%. The specifics of welding under the proposed welding fluxes are determined. The chemical composition of the fluxes, the slag crusts, and the metal in the weld seam are determined by X-ray spectral analysis. The weld seams are studied metallographically. It is possible in principle to use barium–strontium carbonatite as a refining additive to welding fluxes; it also provides a protective atmosphere for the welded metal. By introducing barium–strontium carbonatite, the content of nonmetallic inclusions (nondeforming silicates, point oxides, and brittle silicates) in the weld seam may be reduced, and the desulfurizing properties of the welding fluxes may be enhanced. The introduction of up to 5% barium–strontium carbonatite in welding fluxes based on silicomanganese slag ensures that the metal in the weld seam has ferrite–pearlite structure of Widmanstatten type. The grain size is slightly reduced here: from a score of 4 to 4–5.

Strontium-modified premixed calcium phosphate cements for the therapy of osteoporotic bone defects.

Strontium-releasing calcium phosphate bone cements are promising materials for the clinical regeneration of osteoporosis-related bone defects since they have been shown to stimulate bone formation and at the same time limit osteoclastic bone resorption. Today clinical practice favours minimally invasive surgical techniques, e.g. for vertebral fracture treatment, posing special demands on such cements. We have therefore developed a premixed, strontium-releasing bone cement with enhanced mechanical properties and high radiographic visibility that releases biologically relevant strontium concentrations and thus stimulates cells of the osteogenic lineage. In a pilot experiment we also exemplify its excellent suitability for minimally invasive balloon kyphoplasty procedures.

Effect of Sr–Grain Refining–Si Interactions on the Microstructural Characteristics of Al–Si Hypoeutectic Alloys

The present study was performed on A356.2 alloy to explore the link between the effectiveness of different grain refiner practices and strontium (Sr) modification on both the eutectic silicon (Si) particle morphology and the final grain size. To achieve this objective, several types of grain refiners were added to the molten alloy at 750 °C in different concentrations and for various holding times. Strontium was added in the amount of 200 ppm. Thermal analysis combined with microstructure analysis using optical microscopy and electron probe microanalysis was used to assess the results. It was found that Sr has a certain affinity to react with the boron (B) in Al–5%Ti–1%B master alloy which partially reduced the grain refiner effectiveness. The eutectic Si particles maintained a similar degree of modification as in the non-grain refined Sr-modified condition. Al–4%B used with Sr led to the formation of a new intermetallic (SrB6), resulting in a significant decrease in the modification effect of Sr together with an increase in the obtained grain size. This effect increases at higher levels of added Al–4%B. The presence of excess Si leads to a change in the composition of the Al3Ti phase into (Al, Si)2Ti.

3D imaging and quantification of porosity and intermetallic particles in strontium modified Al-Si alloys

Al-Si alloys are widely used in the automotive and aerospace industries. Porosity is considered to be a major defect in these cast alloys. In this study, the effect of strontium (Sr) modification on porosity formation and intermetallic formation in Al-Si alloys is quantified using X-ray tomography. Quantitative information such as average pore size, shape, pore distribution and intermetallic particle size distribution were evaluated for Sr modified and unmodified Al-Si alloys. Results show that the addition of 400 ppm of Sr increases the porosity by 10% as compared to unmodified Al-Si alloy. Further, Sr addition increases the average equivalent diameter of pores from 2 μm to 18 μm compared to unmodified alloys. A greater number of larger pores were found in the Sr modified alloy, whereas the number of small sized pores was significantly higher in unmodified alloy. The addition of 400 ppm of Sr results in formation of Al-Si-Sr intermetallics with an average equivalent diameter of 4.5 μm. It can be hypothesised that these intermetallic particles act as heterogeneous sites for pore nucleation and significant further growth of porosity in Sr modified alloys.

Effect of a Minor Sr Modifier on the Microstructures and Mechanical Properties of 7075 T6 Al Alloys

The influence of a minor strontium (Sr) modifier on the microstructures and mechanical properties of 7075 Al alloys was investigated in this paper. The grain size of cast 7075 Al alloys was refined from 157 μm to 115 μm, 108 μm, and 105 μm after adding 0.05 wt. %, 0.1 wt. %, and 0.2 wt. % Sr, respectively. The extruded 7075 Al alloys was refined with different degrees of Sr modifier. The mechanical properties were optimum when adding 0.1 wt. % Sr. The ultimate tensile strength (σb) increased from 573 to 598 MPa and the elongation-to-failure (δf) was raised from 19.5% to 24.9%. The microhardness increased from 182 to 195 Hv. The tensile fracture surface via scanning electron microscopy (SEM) revealed a transition from brittle fracture to ductile fracture as Sr increased from 0 wt. % to 0.2 wt. %. The result in this paper proved that the modifier can improve the properties of 7075 Al alloy.

Effect of Solidification Parameters on the Microstructure and Tensile Properties of 319-Type Alloys

The present study was performed on an Al–Si–Cu 319-type alloy using an end-chill mold, while varying the cooling rate along the solidification axis. Good fits for response parameters of percent porosity, maximum pore area, average pore area, maximum pore length and average pore length were obtained from the statistical analysis of the porosity data for the end-chill mold samples. These results strongly support the porosity formation observed in an aluminum A319.2 alloy reported in an earlier study. Tensile samples were T6-heat-treated, and the data obtained from these samples were analyzed statistically. The results show that the ultimate tensile strength (UTS) is sensitive to variations in the porosity and solidification conditions, and varies in a nonlinear fashion with respect to both, while the yield strength is practically unaffected. Ductility is also sensitive to variations in porosity and cooling rate, following a trend similar to that shown by the UTS. Increasing the porosity volume fraction above 0.5 % in the base alloy (unmodified and non-grain-refined) reduces the ductility to negligible levels. Strontium modification and grain refining allow for increases in porosity before the same level of degradation in ductility is observed. The cooling rate significantly influences the ductility at low hydrogen levels. At higher levels, however, hydrogen has a more pronounced effect (porosity related) on the drop in ductility.

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.

Study on the Piezoelectric Behavior and Structural Changes of Strontium Doped PZT Ceramics

Some piezoelectric properties of lead zirconate titanate PbZr0.53Ti0.47O3 ceramic samples sintered at 1100oC for 3 hours has been investigated in this work and compared to the strontium modification at 0.2, 0.4, and 0.6 mol%. Polarization versus Electric Field curve and d33 and Kp piezoelectric parameters was taken at room temperature in order to investigate the correlation with phase amount and lattice parameters of crystalline phases calculated through Rietveld refinement. The results indicated the lead substitution with 0.4 mol% of strontium enhances the d33 and Kp piezoelectric parameters, but there is no systematic variation of the piezoelectric properties with strontium content. By the other hand, tetragonal phase seems plays an important rule on piezoelectric devices operating near the room temperature and some correlations could be found.

Microalloying and modification of steel with natural materials and industrial waste

The use of natural materials and industrial waste in the microalloying and modification of steel is studied. The metallurgical properties of a natural barium–strontium modifier are investigated, and its influence on the melting point of reducing slag is assessed. The results show that its industrial use is very promising. Terra software is used to assess the reduction of barium and strontium from their oxides by silicon and aluminum. The action of barium and strontium on the metal quality is analyzed. The potential of vanadium converter slag in microalloying steel with vanadium is established. The effectiveness of carbon from molten steel in the reduction of vanadium is assessed. Industrial tests are in good agreement with the theoretical findings. Recommendations are made for the optimization of microalloying and modification. The use of the materials here investigated improves the economics of steel production and considerably enhances the quality of the steel produced. The prospects for expanded of use of natural materials and industrial waste are discussed.

Strontium substitution in apatitic CaP cements effectively attenuates osteoclastic resorption but does not inhibit osteoclastogenesis

Strontium ions were discovered to exert a dual effect on bone turnover, namely an inhibition of cell-driven bone resorption and a simultaneous stimulation of new bone tissue formation. A variety of strontium containing calcium phosphate bone cements (SrCPC) have been developed to benefit from both effects to locally support the healing of osteoporotic bone defects. While the stimulating effect of strontium modification on bone forming cells has been demonstrated in a number of studies, this study focuses on the inhibition and/or reduction of osteoclastogenesis and osteoclastic resorption by a strontium substituted calcium phosphate bone cement (SrCPC). Human peripheral blood mononuclear cells (PBMC) were differentiated into osteoclasts in the presence of different Sr2+-concentrations as well as on the surface of SrCPC disks. Osteoclastogenesis of PBMC was shown to be merely unaffected by medium Sr2+-concentrations comparable to those released from SrCPC in vitro (0.05–0.15mM). However, an altering effect of 0.1mM strontium on the cytoskeleton of osteoclast-like cells was shown. In direct contact to SrCPC disks, these cells exhibited typical morphological features and osteoclast markers on both RNA and protein level were formed. However, calcium phosphate resorption was significantly decreased on strontium-containing cements in comparison to a strontium-free control. This was accompanied by an intracellular accumulation of strontium that increased with substrate strontium content as demonstrated by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). This study illustrates that SrCPC do not inhibit osteoclastogenesis but significantly attenuate osteoclastic substrate resorption in vitro. Statement of SignificanceStrontium ions have been shown to promote bone formation and inhibit bone resorption. Therefore strontium is successfully used in the treatment of osteoporosis and also inspired the development of strontium-containing strontium/calcium phosphate bone cements (SrCPC). Studies have shown the positive effects of SrCPC on bone formation, however, the inhibiting effect of strontium on bone resorption in the context of such cements has not been shown so far. We found that the formation of bone-resorbing osteoclasts is not inhibited, but that their resorption activity is decreased in contact to SrCPC. The former is important since those cells play an important role in the bone cell signaling. The latter is a key requirement in osteoporosis therapy, which addresses excess bone resorption.

Combined effect of strontium modifier and antimony refiner on texture and growth mode of eutectic phase in an Al-11Si-2Cu-0.8Zn-0.6Fe cast alloy

Results of electron back-scattered diffraction and transmission electron microscopy studies reveal that the orientation of aluminium in the eutectic phase is different from the surrounding aluminium dendrites and that twin spacing of eutectic silicon increased significantly due to the interaction between strontium and antimony. In addition, the formation of ternary Mg2Sb2Sr intermetallic compound that precedes the eutectic reaction was proposed to be responsible for interaction.

Microstructural characterization and high cycle fatigue behavior of investment cast A357 aluminum alloy

In order to observe the influence of strontium (Sr) modification and hot isostatic pressing (HIP) on an aluminum–silicon cast alloy A357 (AlSi7Mg0.6), the microstructure and the high cycle fatigue behavior of three batches of materials produced by investment casting (IC) were studied. The parts were produced by an advanced IC proprietary process. The main process innovation is to increase the solidification and cooling rate by immersing the mold in cool liquid. Its advantage is to produce finer microstructures. Microstructural characterization showed a dendrite arm spacing (DAS) refinement of 40% when compared with the same part produced by conventional investment casting. Fatigue tests were conducted on hourglass specimens heat treated to T6, under a stress ratio of R=0.1 and a frequency of 25Hz. One batch of material was unmodified but two batches were modified with 0.007% and 0.013% Sr addition, from which one batch was submitted to HIP after casting. Results reported in S–N diagrams show that the addition of Sr and the HIP process improve the 106cycles fatigue strength by 9% and 34% respectively. Scanning electron microscopy (SEM) observation of the fracture surfaces showed a variety of crack initiation mechanisms. In the unmodified alloy, decohesion between the coarse Si particles and the aluminum matrix was mostly observed. On the other hand, in the modified but non HIP-ed alloy, cracks initiated from pores. When the same alloy was subjected to HIP, a competition between crystallographic crack initiations (at persistent slip bands) and decohesion/failure of intermetallic phases was observed. When compared to fatigue strength reported for components produced by permanent mold casting, the studied material are more resistant to fatigue even in the unmodified and non HIP-ed states.

Studies on Partially Melted Zone and Pitting Corrosion Resistance of A356 Aluminium-Silicon Alloy GTA Welds

Gas Tungsten Arc Welding (GTAW) of Pressure Die cast A356 Al-Si alloy with strontium modification was done both with and without filler. The microstructural changes in Weld metal zone (WM), Heat affected zone (HAZ) and Partially Melted Zone (PMZ) were studied. PMZ of aluminium alloy weld is an important region, as it is the weak link in the weldments. It is significantly affected by the welding parameters, filler metal and prior thermal condition. In the present work affect of welding techniques i.e. Continuous Current Gas Tungsten Arc Welding (CCGTAW) and pulsed Current Gas Tungsten Arc Welding (PCGTAW) on microstructure and pitting corrosion resistance of weld metal, Partially melted zone and Heat affected zone in the prior conditions of as cast and T6 conditions were studied. Susceptibility to liquation was found to be less in the weld made in as cast condition of pulsed current GTA welds compared to that of artificially aged condition (T6) of continuous current GTA welds. This was mainly attributed to the silicon enrichment of eutectics at the grain boundaries. Potentiodynamic polarization testing was carried out to study the pitting corrosion behavior of the welds. Pitting corrosion resistance of weld made with pulsed current GTAW of as cast alloy is better than the that of weld made with continuous current GTAW of T6 alloy. This is mainly attributed to the discontinuous eutectic formation at the grain boundary base metal and PMZ.

Influence of strontium in AlSi7Mg0.3 alloy on the tool wear

Al-Si alloys are leading casting alloys based on aluminum. Machining of aluminum alloys is currently frequently used and it is an important area of production. The paper deals with an experiment that was conducted at the Faculty of Production Technology and Management, University of Jan Evangelista Purkyně in Usti nad Labem, where was machined alloy AlSi7Mg0,3. Samples were made for processing from the master alloy AlSi7Mg0,3, subsequently unmodified and modified of strontium Sr. This paper describes the evaluation of tool wear in terms of how or strontium modification may affect (reduce) the tool wear.

A novel strontium(II)-modified calcium phosphate bone cement stimulates human-bone-marrow-derived mesenchymal stem cell proliferation and osteogenic differentiation in vitro

In the present study, the in vitro effects of novel strontium-modified calcium phosphate bone cements (SrCPCs), prepared using two different approaches on human-bone-marrow-derived mesenchymal stem cells (hMSCs), were evaluated. Strontium ions, known to stimulate bone formation and therefore already used in systemic osteoporosis therapy, were incorporated into a hydroxyapatite-forming calcium phosphate bone cement via two simple approaches: incorporation of strontium carbonate crystals and substitution of Ca2+ by Sr2+ ions during cement setting. All modified cements released 0.03–0.07mM Sr2+ under in vitro conditions, concentrations that were shown not to impair the proliferation or osteogenic differentiation of hMSCs. Furthermore, strontium modification led to a reduced medium acidification and Ca2+ depletion in comparison to the standard calcium phosphate cement. In indirect and direct cell culture experiments with the novel SrCPCs significantly enhanced cell proliferation and differentiation were observed. In conclusion, the SrCPCs described here could be beneficial for the local treatment of defects, especially in the osteoporotic bone.

Optimization of Squeeze Parameters and Modification of AlSi7Mg Alloy

Abstract The paper present the examination results concerning mechanical properties of castings made of AlSi7MG alloy in correlation both with the most significant squeeze casting parameters and with the modification treatment. Experiments were planned and held according to the 23 factorial design. The regression equations describing the influence of the squeeze pressure, the mould temperature, and the quantity of strontium modifier on the strength and elongation of the examined alloy were obtained. It was found that the main factor controlling the strength increase is the squeeze pressure, while the plasticity (A5) of the alloy is affected most advantageously by modification. The application of modification treatment in squeeze casting technology enables for production of the slab-type castings made of AlSi7Mg alloy exhibiting strength at the level of 230 MPa and elongation exceeding 14%.

Effects of strontium impurity on the structure and dynamics of Al88Si12 liquid

The effects of strontium modification on the structure and dynamics of Al88Si12 liquid are studied by means of ab initio molecular dynamics simulations. By replacing 0.5% and 4.0% of Al with Sr, we show that the addition of Sr lowers the self-diffusion of Al and Si of the liquid and reduces the nearest-neighbor correlation between Si atoms. The simulation provides an explanation for the change in morphology of the eutectic phases observed in rapidly solidified Al–Si alloys modified with Sr.

Structural and Luminescence Properties of Borate Glass with Lithium and Strontium Modifier Doped with Transition Metal Ions

A system of borate based glass with different modifier but similar dopant was investigated to determine both the structural and photoluminescence properties. The glass sample from the series of x(M):(1-x)B2O3 where 0.2 ≤ x ≤0.7 mole% and M was Li2O and SrO, and the metaborate composition of glass was doped withMn¬¬2+, Fe2+ and Zn2+ ions. The effect of the modifier towards the structural and photoluminescenceproperties in the glass samples was investigated using Fourier-Transfer Infrared (FT-IR) spectroscopy and photoluminescence spectroscopy. Infrared spectrum revealed the traces of BO3 and BO4 units at different modifier and concentration. Significant changes in the host structure showed modification at specific region depending on the type of modifier.The photoluminescence of the samples were studied using the luminescence spectrophotometer. The samples were excited at different emission wavelength to compare the results. This study showed that with the introduce Mn2+, Fe2+ and Zn2+ ions as activators within the host material enhancedphotoluminescence characteristic.

Poisoning effect of bismuth on modification behaviour of strontium in LM25 alloy

Nucleation and growth, temperature measurements and microstructure observations of silicon phase are presented for strontium modified Al–7%Si (LM25) cast alloy treated with bismuth. The results show that addition of bismuth in strontium modified alloys may have a poisoning effect resulting in lost modification of the silicon phase. With increasing Bi/Sr ratio, thermal analysis measurements showed that the eutectic growth temperature increased remarkably to 573°C and recalescence decreased to 0·2°C and the morphology of silicon displayed the same flake-like structure as in the unmodified alloys. Microstructural observation showed that a minimum Bi/Sr ratio of 1·2 which is equivalent to a Sr/Bi ratio of 0·43 is required for effective strontium modification and neutralization of the poisoning effect of bismuth.