Al4Sr Phase Research Articles

Performance evaluation of different carbide inserts in turning of newly developed Al‐12Si‐0.1Sr alloy

AbstractAn Al‐12Si‐0.1Sr alloy ingot was manufactured using a permanent mold casting technique. The microstructure and mechanical properties of this alloy were researched. Effects of different cutting conditions (cutting speed‐V: 200 m/min, 300 m/min, and 400 m/min and feed rate‐f: 0.05 mm/rev, 0.1 mm/rev, and 0.15 mm/rev) on the cutting force (F) and surface roughness (Ra) during machining using uncoated and physical vapor deposition‐ titanium aluminum nitride coated carbide inserts were also revealed. Microstructure of the alloys consists of α phase, intermetallic δ and Al4Sr phases, thin spherical eutectic, and irregular coarse‐shaped primary silicon particles. Cutting force and surface roughness decreased with the increased cutting speed during turning with uncoated, and titanium aluminum nitride coated inserts while they increased feed rate. A built‐up edge and built‐up layer were formed in both cutting inserts. The built‐up edge and built‐up layer decreased with increasing cutting speed and increased feed rate. The cutting force, surface roughness, built‐up edge, and built‐up layer were lower in uncoated inserts compared to the titanium aluminum nitride coated inserts.

Effect of Sr on hot deformation behavior and microstructure of Al-4.6Mg alloy

The hot deformation behaviors of Al-4.6Mg and Al-4.6Mg-0.2 Sr alloys at temperatures of 300–450 ℃ and strain rates of 0.001–1 s−1 were comparatively studied. Optical microscopy (OM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to study the effect of Sr on the microstructures of the alloys. The constitutive equations of Al-4.6Mg and Al-4.6Mg-0.2 Sr alloys were established. The apparent activation energies of the two alloys were 165.632 and 157.456 kJ/mol, respectively. The microscopic analysis showed that Sr had no significant effect on the grains of the as-cast Al-4.6Mg alloy, the precipitation phase changed, and the needle-like Al4Sr phase was formed. During isothermal compression (IC), both alloy samples consisted of slender grains and new quasi-equiaxed grains. Compared with the Al-4.6Mg alloy, the Al-4.6Mg-0.2 Sr alloy had a lower LnZ value, a smaller grain size, and more sufficient dynamic recovery (DRV); in addition, the grain growth of the Al-4.6Mg-0.2 Sr alloy was suppressed. The main textures of the Al-4.6Mg alloy were Goss and cubic textures, which were replaced by cubic and brass textures after adding Sr. During the IC of the Al-4.6Mg-0.2 Sr alloy, a nanoscale precipitated τ phase, which was uniformly distributed inside spherical grains, was formed.

Experimental research on machinability characteristics of Al-9Si alloy: Effect of Sr and Mg additives

In this study, the effects of strontium (Sr) and magnesium (Mg) elements in certain rates added to Al-9Si alloy manufactured using permanent mold casting technique on the structural, mechanical, and machinability properties of these alloys were investigated. While microstructural images of the alloys were obtained with an optical microscope, hardness, tensile strength, and elongation to fracture were determined by conventional methods. The resultant cutting force ( F) and average surface roughness ( Ra) were measured as experimental outputs in the turning process. It was observed that Al-9Si alloy comprised of α-Al, eutectic Al-Si, β, and primary Si phases. The addition of Sr to the Al-9Si alloy led to the formation of the Al4Sr phase and the transformation of the β phase into the δ phase. The addition of Mg to Al-9Si-0.1Sr alloy caused the δ phase to transform into the π phase. The hardness of the tested alloy increased significantly with the Mg addition. The yield strength and tensile strength of them increased with both Sr and Mg additions. On the other hand, elongation to fracture value of the Al-9Si alloy increased with Sr addition while it decreased with the Mg addition. The F and Ra values obtained from the Al-9Si alloy increased with Sr addition in the turning process while decreased with Mg addition. The results obtained from turning tests were discussed based on the mechanical properties of alloys.

Hot compression and industrial extrusion characteristics of an as-cast Al-10Sr master alloy

Abstract The mechanical properties and castability of Al-Si-based alloys can be remarkably improved by adding Al-Sr master alloy, which modifies the structure and morphology of eutectic silicon. The size of Al4Sr phases in Al-Sr master alloy has been found to take key effect in Sr-modification. To obtain optimized processing parameters and understand the refinement mechanisms of Al4Sr phases during plastic deformation, the hot compression and industrial extrusion characteristics of an as-cast Al-10Sr master alloy were systematically investigated in this work. The results showed that the flow behavior of the Al-10Sr master alloy can be well described by a constitutive equation with the hot deformation activation energy of 222.23 kJ/mol. The obtained optimum processing region was located at temperature of 460–530 °C and strain rate of 0.2–1 s−1 from the established processing maps. During hot compression testing, plastic deformation mainly occurred in soft Al matrix and the Al4Sr phases were slightly broken. During industrial extrusion process, the Al4Sr phases were refined effectively based on the above optimum processing conditions. Comparing to conventional extrusion process, repetitive Conform process showed better ability in refining Al4Sr phases. After three repetitive Conform passes, the length of Al4Sr phases decreased from 80 to 11 μm and the width decreased from 25.6 to 8.3 μm, and the Al4Sr phases were also distributed homogeneously. The in-depth refinement mechanisms of Al4Sr phases during plastic forming were also discussed based on microstructural examinations and finite element analysis.

An analysis of microstructure and impression creep response of squeeze-cast AZ91–xBi–ySr alloys

ABSTRACTThe present investigation deals with the microstructural modification following the Bi + Sr additions to the squeeze-cast AZ91 alloy and its effect on impression creep response. The Bi + Sr additions form the Al4Sr and Sr2Bi phases besides the α-Mg and β-Mg17Al12 phases, and improves creep resistance of the AZ91 alloy. The AZ91 + 1.0Bi + 0.5Sr alloy reveals the best creep resistance among the alloys. The stress exponent and the activation energy values of all the alloys are in the range of 4–7 and 100.2–112.7 kJ mol−1, respectively, depicting the pipe diffusion-controlled dislocation creep is the governing creep mechanism. The post-creep microstructural study confirms several dislocations pile-ups around the Al4Sr and Sr2Bi phases resulting in improved creep resistance of the modified AZ91 alloys.

Microstructure, tensile properties and free bulge formability of Sr- and Y-containing AZ31 alloy sheet produced by twin-roll casting and sequential hot rolling

The effects of Sr and Y on microstructure, tensile property and free bulge formability of AZ31 alloy sheet produced by twin-roll casting and sequential hot rolling were investigated to improve the mechanical properties and formability of the AZ31 alloy. Sr and Y addition can form Al4Sr, Al2Y and Al3Y phases which can impede dislocation movement and promote dynamic recrystallization during the rolling deformation and decrease the lattice resistance to dislocation motion by decreasing Al solubility in the alloy, resulting in finer grains, lower dislocation density and no twinning generating in the twin-roll casting and sequential hot rolling (TRC-HR) AZ31–1.3Sr–1.0Y alloy. The maximum stress and elongation of the alloy increase significantly after adding Sr and Y. The average cavity and grain sizes of the TRC-HR AZ31–1.3Sr–1.0Y alloy are smaller, resulting in higher elongation in the alloy. The addition of Y and Sr can effectively improve the free bulge formability and the thickness uniform of the alloy. The Al4Sr, Al2Y and Al3Y phases can inhibit the grain growth by obstructing dislocation motion or grain boundary slip, resulting in smaller grain size of AZ31–1.3Sr–1.0Y alloy bulge parts.

The influence of hot extrusion deformation on microstructure evolution, tensile properties and corrosion behavior of Mg–3Al–0.5Mn–0.5Sr alloy

A novel microalloyed Mg–3Al–0.5Mn–0.5Sr (AMJ300) alloy was designed and prepared. Then the original structure of as-cast alloy was optimized by hot extrusion. The influence of extrusion on microstructure, corrosion and tensile properties of as-cast AMJ300 alloy were studied by OM, SEM, EDS, XRD, TEM, electrochemical workstation and tensile tests. The results indicated that α-Mg, Al8Mn5 and Al4Sr phases constitute the AMJ300 alloy. Furthermore, the microstructure of alloy was further refined after extrusion, which indicates that the microstructural evolution during extrusion was governed by dynamic recrystallization. The fine and close of structure and the morphology change of intermetallic compounds greatly improved the corrosion resistance of AMJ300 alloy. The results of corrosion rate, corrosion current and corrosion morphology showed that the corrosion resistance of as-cast alloy could be significantly improved by extrusion. The main corrosion products of AMJ300 alloy in 3.5 wt.% NaCl solution was Mg(OH)2. After extrusion, the tensile properties of AMJ300 alloy was significantly improved. The tensile strength reached 349 MPa, the yield strength reached 229 MPa, and the elongation reached 13.2%. Compared with the as-cast alloy, the tensile strength, the yield strength and the elongation increased by 218.1%, 248.9% and 173.7% respectively

Effect of Strontium and Magnesium Additions on the Microstructure and Mechanical Properties of Al–12Si Alloys

In this study, a binary Al–12Si, eight ternary Al–12Si–Sr, and six quaternary Al–12Si–0.1Sr–(0.2–1)Mg alloys were produced by permanent mold casting. It was observed that microstructure of the binary alloy consisted of the phases of aluminum rich α grains (dendrites), primary silicon, plate like β and eutectic Al–Si containing needle like silicon particles. The ternary alloys have fine and globular (modified) eutectic silicon particles and higher volume fraction of α (Al) dendrites than binary alloys. They also contained Al4Sr phase after 0.02 wt% Sr, in addition to the phases in the binary alloy. This phase got coarse when the strontium ratio exceeded 0.1%. It was observed that the plate like β phase seen in the binary alloys transformed into the fibrous form δ phase in the ternary alloys. Magnesium addition resulted in transformation of δ phase into script like π phase, and the formation of lamellar like Mg2Si phase when the ratio of it in the quaternary alloys reached the 0.6 wt%. The lamellar like form of Mg2Si phase changed to Chinese-script type after the 0.6 wt% Mg. The results showed that hardness, yield and tensile strength of the Al–12Si–Sr alloys increased with increasing strontium content up to 0.1 wt%. The results also showed that hardness of the quaternary alloys increased with increasing magnesium content, while yield and tensile strength increased only up to 0.6 wt% Mg.

A Comparative Study on Microstructure, Mechanical and Tribological Properties of A4, AE41, AS41 and AJ41 Magnesium Alloys

Microstructure, tensile and wear properties of as-cast A4 (Mg-4Al), AE41 (Mg-4Al-0.5Ce-0.5La), AS41 (Mg-4Al-1Si) and AJ41 (Mg-4Al-1Sr) alloys were investigated, and the results were compared with each other in this study. Microstructures were investigated by XRD, optical and scanning electron microscopes. Tensile tests were conducted at both room and elevated temperatures. Tribological properties were examined by pin-on-disk wear tests under different applied loads. Microstructure characterizations revealed that the volume fraction of second phases considerably increased by alloying additions of 1 wt.% Ce/La, Si and Sr. The microstructure of A4 alloy consisted of α-Mg grains and divorced β-Mg17Al12 phases. After individual alloying additions of 1 wt.% Ce/La, Si and Sr, the secondary phases were primarily replaced by needle-shaped and massive blocky-shaped Al11(Ce,La)3 phases in AE41 alloy, Chinese-script-type Mg2Si phases in AS41 alloy and divorced globular-like and massive blocky-shaped Al4Sr and (Mg,Al)17Sr2 phases in AJ41 alloy. The tensile tests showed that at both room and elevated temperatures alloying additions of 1 wt.% Ce/La, Si and Sr resulted in an increase in the strength but a decrease in the ductility. Among the studied alloys, AS41 alloy exhibited the best strength. Wear test results showed that AE41 and AJ41 alloys similarly exhibited the best wear resistance owing to the presence of hard and dense intermetallics. Abrasion was the main wear mechanism under low applied loads while delamination, adhesion and oxidation mechanisms were majorly observed under high applied loads.

Dynamic Recrystallization Behavior and Corrosion Resistance of a Dual-Phase Mg-Li Alloy

The hot deformation and dynamic recrystallization behavior of the dual-phase Mg-9Li-3Al-2Sr-2Y alloy had been investigated using a compression test. The typical dual-phase structure was observed, and average of grain size of as-homogenized alloy is about 110 µm. It mainly contains β-Li, α-Mg, Al4Sr and Al2Y phases. The dynamic recrystallization (DRX) kinetic was established based on an Avrami type equation. The onset of the DRX process occurred before the peak of the stress–strain flow curves. It shows that the DRX volume fraction increases with increasing deformation temperature or decreasing strain rate. The microstructure evolution during the hot compression at various temperatures and strain rates had been investigated. The DRX grain size became larger with the increasing testing temperature or decreasing strain rate because the higher temperature or lower strain rate can improve the migration of DRX grain boundaries. The fully recrystallized microstructure can be achieved in a small strain due to the dispersed island-shape α-Mg phases, continuous the Al4Sr phases and spheroidal Al2Y particles, which can accelerate the nucleation. The continuous Al4Sr phases along the grain boundaries are very helpful for enhancing the corrosion resistance of the duplex structured Mg-Li alloy, which can prevent the pitting corrosion and filiform corrosion.

Effect of the addition of Sr modifier in different conditions on microstructure and mechanical properties of T6 treated Al-Mg2Si in-situ composite

The present work was carried out to investigate the effect of different sizes of Al4Sr phase in Al-10Sr alloy on the microstructure and mechanical properties of T6 treated Al-(10/15)Mg2Si in-situ composites. The finer Al4Sr phase could be obtained via rolling and hot-extruding the as-cast Al-10Sr master alloy, which thereby influenced its modification performance. The results showed that primary Mg2Si was transformed from imperfect octahedron to regular polygon morphology and eutectic Mg2Si was changed from Chinese script type to fibrous or fish-bone structure after the addition of Sr modifier in three conditions (as-cast, rolled and extruded). Moreover, the finer Al4Sr phase was beneficial to further refine the primary Mg2Si accompanied with a more uniform size distribution, and the spheroid transformation of eutectic Mg2Si was remarkably promoted during T6 heat treatment process. As a consequence, the superior ultimate tensile strength and elongation of T6 treated Al-10Mg2Si and Al-15Mg2Si were obtained (291 MPa and 4.45%, 289 MPa and 2.36%, respectively). The results of EDS analysis showed that Sr distributed at the interface of the primary Mg2Si, which lead to the morphology transformation of Mg2Si particles. Thus, this study offered a simple optimized method to enhance the modification efficiency of Sr on Al-Mg2Si composites.

Effects of minor Sr addition on the microstructure, mechanical properties and creep behavior of high pressure die casting AZ91-0.5RE based alloy

Effects of minor Sr (x=0, 0.2, 0.6, 1.0wt%) addition on microstructure, mechanical properties and creep behavior of high pressure die casting AZ91-0.5RE based alloys were thoroughly investigated. Experimental results show that the addition of Sr to HPDC AZ91-0.5RE based alloys can refine the microstructure including externally solidified crystal α-Mg and eutectic compound β-Mg17Al12. On the other hand, when the content of Sr reaches 1.0%, a small amount of plate-like Al4Sr phase can be formed. Moreover, minor of Sr addition can significantly decrease the volume fraction of β-Mg17Al12 precipitates of AZ91-0.5RE based alloys. In addition, the mechanical properties of AZ91-0.5RE based alloys can be improved remarkably with Sr addition, and the alloy containing 0.2% Sr exhibits the best mechanical properties at ambient temperature. Fractographic analyses demonstrate that the fracture modes of the alloy without and with Sr are quasi-cleavage fracture and ductile fracture, respectively. Furthermore, Creep properties of HPDC AZ91-0.5RE based alloys were obviously improved by adding Sr element. And creep mechanisms of the alloys with and without Sr at 150°C/30–70MPa and 50MPa/140–160°C are both considered to be dislocation climb controlled creep based on the analyses of the stress exponent and apparent activation energy. The AZ91-0.5RE-1.0Sr alloy presents the best creep resistance among the studied alloys, which is mainly attributed to the presence of thermally stable intermetallic compound of Al4Sr phase at the grain boundaries.

Preparation of Al-Sr master alloys by the aluminothermic reduction of SrO using aluminum scrap at pilot plant scale

Al-Sr master alloys were prepared by aluminothermic reduction of SrO in molten aluminum processed from scrap. The trials were performed at 500 kg pilot plant scale, using a gas operated furnace with a silicon carbide crucible. The effect of temperature, initial magnesium concentration and agitation speed on the aluminothermic reduction rate of SrO powders was studied. Moreover, the microstructure of Al-Sr master alloys prepared has been analyzed by means of optical microscopy, X-ray diffraction (XRD), and scanning electron microscopy (MEB). In this sense, the morphology of secondary constituents and the structure of Al4 Sr phase were evaluated. The results showed that the aluminothermic reduction technique is useful for producing Al-Sr master alloys, observing the presence of the Al4 Sr intermetallic phase as the main secondary constituent.

Effect of Billet Preheating Temperature on Continuous Extrusion Forming of Al-Sr Alloy

Abstract Based on numerical simulation and process experiment, this study investigates the effect of billet preheating temperature on continuous extrusion forming of Al-Sr alloy and the microstructure and mechanical properties of products. The numerical simulation results show that the temperature starts to rise after the billet enters into the cavity during the continuous extrusion of Al-Sr alloy, and the maximum temperature appears at the die exit. Moreover, the maximum equivalent stress appears in the right-angle bending zone. The billet preheating temperature increases from 300 °C to 480 °C, the maximum temperature of billet in cavity increases from 483 °C to 512 °C and the temperature at the die exit increases from 493 °C to 522 °C. The experiment results show that the Al4Sr phase morphology in products changes from granular to blocky and increases in size. The tensile strength decreases from 114 MPa to 104 MPa, and the elongation increases from 8.4% to 10.5%.

Influence of additions of Sb and/or Sr on microstructure and tensile creep behaviour of squeeze-cast AZ91D Mg alloy

The effects of individual and combined additions of Sb and Sr on microstructure and creep properties of the squeeze-cast AZ91D alloy have been investigated. For comparison, the same has also been studied on the as-cast AZ91D alloy without any addition. The results indicate that both individual and combined additions refine the grain size and β-Mg17Al12 phase, which is more pronounced with combined addition. Besides α-Mg and β-Mg17Al12 phases, a new rod-shaped Mg3Sb2 and an irregular shaped Al4Sr phases are formed following individual additions of Sb and Sr in the AZ91D alloy. With combined additions, both Mg3Sb2 and Al4Sr phases are formed in the AZ91D alloy. All the alloys have been creep tested at a temperature of 175°C and at an initial stress of 70MPa. All the modified AZ91D alloys exhibit superior creep resistance as compared to the base AZ91D alloy. Individual addition of Sb is more effective as compared to the individual addition of Sr in improving creep resistance of the AZ91D alloy owing to the higher thermal stability of the Mg3Sb2 phase. Among the modified alloys, the best creep resistance is obtained in the AZ91D alloy pertaining combined addition of both Sb and Sr owing to the reduced amount of β-Mg17Al12 phase and increased amount of high melting point Mg3Sb2 and Al4Sr intermetallic phases.

Evolution of Morphological Character of Al4Sr Phase Under Different Solidification Conditions

Evolution of Morphological Character of Al4Sr Phase Under Different Solidification Conditions

Microstructure evolution and mechanical properties of Mg–9Li–3Al–2Sr alloy in change channel angular pressing

Change channel angular pressing is a specially designed continuous processing technique to prepare bulk ultrafine grained materials. The extrusion process and structure evolution of Mg–9Li–3Al–2Sr alloy were analysed. The long strip phases of α-Mg and β-Li were sheared into short pieces during extrusion. The continuous distribution Al4Sr phases were extruded into small particles, which are mainly observed in the α/β phase interface and β-Li matrix phase. Structure homogeneity can be achieved, and the mechanical properties were improved with one pass processing. The effect of Al4Sr phase on the microstructure and mechanical properties of Mg–9Li–3Al–2Sr alloy was observed to be different due to the various extrusion modes and parts.

The Influence of Strontium on the Microstructure of Cast Magnesium Alloys Containing Aluminum and Calcium

Abstract The structure of Mg-9Al-2Ca-xSr alloys is composed of a-Mg grains and the Al2Ca and Al4 Sr phases in the interdendritic areas. These phases are formed as a result of eutectic reactions. Globular particles of the Al8Mn5 phase are observed within the interior of the grains. The addition of strontium to Mg-9Al-2Ca-0.4Mn alloys causes the formation of the Al4Sr phase and increase of its volume fraction with increasing strontium levels. Moreover, increase of the strontium amount causes a decrease of aluminum content in the a-Mg solid solution.

First-principles investigation of the structural, electronic and elastic properties of Al2Ca and Al4Sr phases in Mg-Al-Ca(Sr) alloy

First-principles calculations have been carried out to investigate the structural stabilities, electronic structures and elastic properties of Mg17Al12, Al2Ca and Al4Sr phases. The optimized structural parameters are in good agreement with the experimental and other theoretical values. The calculated formation enthalpies and cohesive energies show that Al2Ca has the strongest alloying ability, and Al4Sr has the highest structural stability. The densities of states (DOS), Mulliken electronic populations, and electronic charge density difference are obtained to reveal the underlying mechanism of structural stability. The bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio are estimated from the calculated elastic constants. The mechanical properties of these phases are further analyzed and discussed. The Gibbs free energy and Debye temperature are also calculated and discussed.

Preparation of a novel Al–3B–5Sr master alloy and its modification and refinement performance on A356 alloy

A novel Al–3B–5Sr master alloy has been prepared through in situ synthesis method in Al melt. The as-prepared master alloy was then used to modify A356 alloy. The microstructures of the Al–3B–5Sr alloy and modified A356 alloy were investigated. The results showed that the Al–3B–5Sr alloy mainly consisted of phases of α-Al and granular SrB6, while the Al–3B–5Sr–7Si alloy contained irregular blocky Al4Sr phase, AlB2 and Si besides the above-mentioned phases. Satisfactory grain refining and modifying effects were obtained by the addition of Al–3B–5Sr alloy (0.5wt.%) to the A356 alloy. Meanwhile, the morphology of eutectic silicon was changed from needle/platelike form to fibrous/globular form. The sizes of the α-Al dendrites decreased from ∼1000μm to ∼300μm. The mechanical properties of A356 alloy has been improved significantly with 0.5wt.% Al–3B–5Sr alloy addition.