Cast Grain Research Articles

Regulating the grain refinement and rolling properties of coarse-crystalline Mg-Zn-Gd-Ca-Mn alloy through multi-pass cold rolling and annealing

The newly developed Mg–Zn-RE (rare earth) alloy sheet shows significant prospects for 3C applications due to its superior room-temperature malleability compared to the commercial AZ31 alloy. However, the casting ingots of these alloys often exhibit coarse grains due to low alloying element content and the absence of the grain-refining element Zr, making them susceptible to significant cracking while hot-rolling. This study applies a multi-pass cold rolling technique with minimal reduction to a cast Mg–Zn-Gd-system alloy characterized by coarse grains, followed by a static annealing process to enhance its rolling capability. The impact of cold rolling and annealing temperatures on microstructure, plastic deformation mechanism, and static recrystallization (SRX) behavior were studied. It was found that multi-pass cold rolling with minimal decrease promoted the generation of more twins and slip lines, resulting in more uniform deformation and a substantial accumulated rolling strain of 10 %. Consequently, the significant accumulated strain, coupled with stress concentration at positions such as grain boundaries, twin boundaries, and dislocation tangles, acted as nucleation sites for complete static recrystallization at a specific annealing temperature of 375 °C. As a result, the coarse cast grains were successfully refined from 400 μm to 37 μm. Fortunately, this improvement has significantly enhanced the hot-rolling qualities, removing fractures throughout the process. This advancement not only enables industrial-scale rolling but also enhances production efficiency.

Solidification of two fused cast Al2O3–ZrO2–SiO2 materials in an aero acoustic levitator

Due to their excellent high-temperature properties and corrosion resistance, AZS materials are widely used in glas making. Two industrially available fused cast AZS materials were chosen for this study. One composition was close to the ternary eutectic of zirconia, mullite, and corundum. The other material was close to mullite composition with approx ten wt% ZrO2. The microstructure and phase composition of the received material was analyzed. Additionally, the materials were remelted in an aero acoustic levitator. The fused cast grains and the remelted samples showed significant differences in the microstructure and phase composition. Due to the high cooling rates and homogeneous nucleation under containerless conditions, both materials tended to form a glassy phase. Cooling samples with a pre-existent nucleus or controlled conditions yielded a fine-grained crystalline microstructure. For conventional cooling, the silica and alumina-rich material exhibited large corundum precipitates. In contrast, the containerless processed sample showed primary precipitation of mullite.

Effect of Sm + Er and Heat Treatment on As-Cast Microstructure and Mechanical Properties of 7055 Aluminum Alloy.

The 7055 aluminum alloy is an ultra-high strength aluminum alloy, which is widely used in the aerospace field and new energy automobile manufacturing industry. As it retains high strength, its plastic deformation ability needs to be improved, which limits its application in plastic processing. In this study, the cast grains of the 7055 aluminum alloy were refined by adding Sm + Er, and the proper heat treatment procedure was utilized to further precipitate the rare earth phase in order to increase the alloy's strength and toughness. The grain size, microstructure and phase were characterized by optical microscopes (OMs), scanning electron microscopy-energy spectrum (SEM-EDS) and a XRD diffractometer (XRD). The macroscopic hardness, yield strength and tensile strength of alloy materials were measured by a hardness meter and universal electronic tensile machine. The results showed that the as-cast sample and the heat treatment sample all contained Al10Cu7Sm2 and Al8Cu4Er rare earth phases. But, after heat treatment, the volume percentage of the rare earth phase dramatically increased and the dispersion was more unified. When 0.3 wt.%Sm and 0.1 wt.%Er were added, the grain size could be refined to 53 μm. With the increase in the total content of rare earth elements, the refining effect first increased and then decreased. Under 410 °C solid solution for 2 h + 150 °C and aging for 12 h, the macroscopic hardness, yield strength, tensile strength and elongation of 0.3 wt.%Sm + 0.1 wt.%Er + 7055 as-cast samples were 155.8 HV, 620.5 MPa, 658.1 MPa and 11.90%, respectively. After the addition of Sm and Er elements and heat treatment, the grain refinement effect of 7055 aluminum alloy was obvious and the plastic property was greatly improved under the premise of maintaining its high-strength advantage.

Effect of Ti-B Grain Refiners on Wear and Corrosion of the A332 Alloy with Sr Modification

Grain refiners play a critical role in changing characteristics and properties of casting aluminum alloys. The Al-Si alloy (A332) is one of the most popular hypoeutectic alloys with a large range of industrial applications. It has a varied phase and morphology; however, it features problems with acicular-shaped eutectic phase, and generally exhibits dendritic cast grain type. To change this situation, the Sr element acts as a modifier of eutectic, which, along with a grain refiner may increase mechanical properties. In this work, two different grain refiners (Al5Ti1B, Al5Ti2B) were applied to the A332 alloy modified with Sr, and analyzed in relation to grain size, hardness, corrosion resistance, and wear behavior. Corrosion tests in 3.5 wt.% NaCl solution, nanoindentations, and Heyn’s method to analyze grain size and microhardness as optical and SEM images were made to examine the changes caused by grain refiners. A reduction in grain size was achieved, and the influence in size and hardness of the β-Fe phase was verified in the wear and corrosion analyses.

Effect of minor Sc addition on high temperature tensile behavior of Al–7Zn–2Mg–2Cu–0.2Zr alloy

Alloys of Al–7Zn–2Mg–2Cu–0.2Zr and Al–7Zn–2Mg–2Cu–0.2Zr–0.2Sc were prepared by extrusion casting. Elongation–to–failure tests and strain–rate–change tensile tests were conducted at 300, 350, 400 and 450 °C, and deformation mechanisms were investigated based on microstructure, stress exponent and deformation activation energy. The results show that the 0.2 wt% Sc addition improves both tensile ductility and strength by refining grains and forming second phase particles. Primary Al3(Sc, Zr) particles precipitate during solidification and refine the as–cast grains, and secondary Al3(Sc, Zr) particles precipitate and interact with moving dislocations during high temperature deformation. The Sc addition has no significant effect on high temperature deformation mechanism. The deformation of both alloys is dominated by dislocation creep strengthened by second phase particles at 300 and 350 °C. Such strengthening effect weakens with the increase in temperature, and the deformation transfers to solute–drag dislocation creep at 450 °C.

Optimization of modification of silumin alloy with Al-Ti-B ligature obtained from dispersed wastes of mechanical engineering by electroslag casting

In this research the process of modifying the AK7 alloy with an experimental master alloy based on the Al-Ti-B system, made from machine-building chip waste, using a combination of powder metallurgy and electroslag casting processes, was studied and optimized. The adequate linear model was obtained on the basis of the study, carried out according to the plan of a full factorial experiment, in which the controlled factors were: the mass ratio of titanium- and boron-containing materials in the charge composition. The role of the solvent in the charge composition was played by the chip waste of the AK7 cast alloy.The response of the cybernetic system was the size of the cast grain of the modified AK7 alloy. The grain-grinding effect of controlled factors has been established. The minimum possible size of the cast grain of the modified AK7 alloy is established with a 95% probability at the level of 250 microns.

Efficiency of different commercial TiBAl grain refiners on refinement of pure aluminum cast structures

Industries largely rely on empirical tests to determine what composition and amount of TiBAl grain refiners to add during the casting of aluminum alloy for cast grain structure refinement. TiBAl grain refiners are aluminum master alloys having intermetallic particles within the aluminum matrix, these particles are mainly made of Ti and Al borides, having higher melting point than aluminum matrix. Addition of them to the melt, induces heterogeneous nucleation of aluminum cast grain structures, which promotes solidification of fine equiaxed grains at expense of columnar grain structures. This yields in grain refinement of cast structures, and is beneficial to mechanical and surface treatment properties on the final product. Very often in industrial practice during casting, whether a grain refiner is suitable for a given alloy, the amount to be added in the melt, and what cooling rates to use, are questions remain and reaching the balance becomes a cumbersome practice, and leads to pernicious material’s properties. This study aims to explore the refinement efficiency of three variants of locally supplied TiBAl grain refiners on the microstructure of cast pure aluminum (CPAl). A standard test method of TP-1 was adopted and the efficiency of TiBAl grain refiners was determined according to the average grain sizes. It was found that Al-3Ti-1B alloys from different suppliers yield different grain sizes, however, Al-5Ti-1B alloy has better efficiency than Al-3Ti-1B alloy system on CPAl material. The optimum holding time for CPAl melt at 750℃ is 5 minutes to achieve a fine grain size.

WAYS TO INCREASE PLASTICITY IN DEFORMATION OF TITANIUM ALLOYS WITH MINIMIZATION OF ENERGY COSTS

This article dial with study, which was carried out to increase the ductility and deformability of titanium alloys BT1-0 and BT6, as well as the formation of highly plastic β-phase emissions in the microvolumes of the alloy. It was determined that the reason for the satisfactory combination of high plastic and impact characteristics with significant strength (σв> 800 MPa) were the following factors: the formation of a significant amount of metastable β-phase, has high plasticity and favorable morphology of the structure in the form of quasi-eutectoid, in which α -phase alternates with plastic β-layers. Research and experiments based on the new concept have proven the prospects of microalloying titanium with a non-deficient effective alloying element, iron. It also shows the real possibility of using much cheaper low-grade sponge-titanium (compared to high-purity sponge titanium) in the smelting of ingots and their processing with a decrease in energy consumption of processing processes and significant economy of titanium. Analysis of these experimental data allowed us to draw the following conclusions. With an increase in the amount of iron in the alloys of the Ti-Fe system, the yield strength and Brinell hardness naturally increased. As shown, iron "loosens" the crystal lattice of titanium and can’t increase the strength of the interatomic bond. Therefore, the nature of the strengthening of titanium iron is different. It is due to the following: grinding of grain in cast and forged states under the influence of iron. It was found that the size of cast grains decreased tenfold during doping titanium alloys by iron. Thus, with increasing concentration of iron in the titanium alloys, the length of the grain boundaries, which were an obstacle to the movement of dislocations, increased sharply.

Activated flux TIG welding of dissimilar SS202 and SS304 alloys: Effect of oxide and chloride fluxes on microstructure and mechanical properties of joints

Low depth of penetration limits the use of favored tungsten inert gas (TIG) welding process for joining of ferrous and non-ferrous metals, demanding weld bead profile of high quality. This article aims to study the effect of chloride and oxide fluxes viz. calcium chloride (CaCl2) and ferric oxide (Fe2O3) on micro-structural and mechanical properties of TIG welded joints of dissimilar SS304 and SS202 steels. Results reflected that use of oxide and chloride fluxes significantly affects the weld bead geometry, bead dimensions and penetration. The use of oxide flux resulted in complete penetration and approximately linear root of weld with good fusion of both the base metals. Fusion zone showed columnar dendritic cast grain structure while coarse grain structure was obtained in heat-affected zone. Fusion zone hardness was higher than SS304 base metal and an opposite trend observed for SS202 irrespective of welding condition. Fine grained heat affected zone hardness was higher than coarse rain for all welding conditions.

Grain refinement of hypoeutectic Al-7wt.%Si alloy induced by an Al–V–B master alloy

The current study investigates the grain refinement of an Al-7wt%Si alloy with addition of Al–V–B master alloy. It is found that the Al–V–B master alloys can overcome the Si poison effect on grain refinement and refine the as cast grain structure of the Al-7wt%Si alloy effectively. A remarkable grain refinement has been achieved by using an Al–3V–1B master alloy with the combined inoculation of 0.015 wt% V and 0.005 wt% B, compared to that obtained by separate inoculation of Al–5V and Al–3B master alloys with the same concentrations of V and B. The corresponding XRD analysis on the Al–5V and Al–3V–1B master alloys and extracted particles from the Al–3V–1B master alloy show that the active nuclei are VB2 particles. The employment of the new Al–3V-1.28B master alloy optimized according to the atomic ratio of V:B = 1:2 produced the finest grain size in the Al-7wt.%Si alloy compared with the commercial Al–3Ti–1B and Al–5Ti–1B master alloys. This study indicates that the Al–V–B master alloy has the potential to be an effective grain refiner for Al–Si alloys.

Mechanisms of TiAl alloys isomorphic inoculation from cryo-milled Ti-Al-Nb powders

Isomorphic inoculation has recently been introduced by the authors as a successful method to grain refine cast titanium aluminides [1]. Analyses of the cast grain size together with introduced particle size distributions revealed anomalously high grain refinement efficiency which was attributed to the particles breaking up during the holding stage prior to solidification [2]. In the present work, the microstructure of the inoculant powders is investigated in both the cryo-milled state as well as after simulated thermal cycles to reproduce their heating and holding in the melt. Results show that milling time does not impact the grain size in the particles, only their size distributions. Heat treatments between 1500 and 1600°C for short periods of time allowed the activation energy for grain growth and evaluation of the grain size evolution in the particles during the isomorphic inoculation process to be determined. Assuming that grain boundary melting is the predominant break up mechanism, a model to estimate dissolution of the powders is presented which includes diffusion and fluid flow. Despite its relative simplicity, the predicted number of particles remaining after heating and holding, which lead to grains in the as-cast structure, are in good agreement with the measured grain size. Finally, the paper summarizes the main features and mechanism making isomorphic inoculation a promising route for grain refining as-cast alloys.

Effect of nitrogen on grain growth and formability of Ti-stabilized ferritic stainless steels

The relationship between the grain size of as-cast and cold rolled 16%Cr ferritic stainless steel and the surface roughness defect, called ridging during forming was investigated. The ridging height corresponded to the grain size of the as-cast sample. The nitrogen content of 140 ppm yielded the minimum grain size and the minimum ridging height observed, whereas the nitrogen content of 50 ppm yielded the maximum grain size and the maximum ridging height observed. Ridging results from different plastic anisotropies of band structure composed of colonies. Through the EBSD analysis, the texture of mixed colonies composed of ND//{112} and ND//{331} in the 50 ppm nitrogen steel underwent more severe ridging than the randomly texture in the 140 ppm nitrogen steel sample. Therefore, an effective means to reduce the ridging of ferritic stainless steel during the forming process is to form a random texture by enhancing the formation of fine equiaxed grain during the casting process. During equal holding times at 1200 °C, the 80 ppm nitrogen sample was definitely coarsened, whereas the 200 ppm nitrogen sample underwent slower grain growth. Zener pinning force, which is proportional to the number of TiN particles on grain boundaries, was relatively strong in samples of 200 ppm nitrogen content, corresponding to slower grain growth. Although the Zener pinning force great affected with increasing nitrogen content, there may not affect the trend of initial cast grain size to be changed as much during annealing.

Research and Development of Vacuum - Lined Ladle

Due to defect of poor heat preservation property, the common steel ladles can’t pour numbers of boxes by one bag for special steel, such as high manganese steel which is sensitive to casting temperature, casting grain size and mechanical properties. The common steel ladles cooling fast often cause cold ladle and misrun. For better insulation, a vacuum insulation layer was added to the ladle to maintain the temperature of the molten steel, reduce the heat absorption of molten steel by ladle and reduce heat exchange with the outside world. The test results showed that the vacuum-lined steel ladle had a desired insulation performance which was much better than ordinary ladle. It improved the properties of castings and also had distinct energy - saving effect. Its good insulation performance brought a series of advantages, such as heating up fast during preheating of ladle, pouring temperature of molten steel could be further reduced, refining the casting grain size, improving the mechanical properties of the casting and wear resistance. Good insulation performance also could extend pouring time. At the same time, the low temperature ladle wall brought good working environment to foundry workers.

Fuel regression behavior of swirling-injection end-burning hybrid rocket engine

Burning experiments were conducted to better understand the fuel regression behavior in a swirling-injection end-burning hybrid rocket engine using paraffin wax/gaseous oxygen propellant. The oxidizer mass flow rate, grain diameter, and the distance between the oxidizer injector and the grain end-surface were the variable parameters taken as influencing the regression rate. The engine attained an overall axial regression rate as high as approximately 5 mm/s, whereas unstable combustion occurred with increasing burning time owing to low melting temperature of paraffin wax. The fuel grain with a diameter of 90 mm also resulted in unstable combustion caused by the initial shallow crack of the cast grain. The radial distribution of the local regression rate exhibited dependency on the radial position and had two peaks: close to the periphery and the middle of the chamber. From the analogy of the heat transfer at the end surface in a vortex flow chamber, the controlling parameter of the overall axial regression rate was derived. Since this parameter depends on the distance between the oxidizer injector outlet and the fuel grain end-surface, to hold the grain end-surface by using some kind of actuator is necessary to attain constant O/F combustion.

Influence of modification by superdispersed powder of aluminum oxide on lead-tin bronze structure

Lead-containing tin bronzes are a good antifriction material. The area of their application is limited because of low strength properties. It is possible to enhance the strength properties by changing their structure using modification by nanopowders. This article presents data on the influence of admixtures of the aluminum oxide nanopowder on the structure of the cast bronze (with lead and tin). For the castings, containing different amounts of the prepared modifier based on aluminum oxide, metallographic studies and structural studies were undertaken. Based on the results of the work, the concentrations of the aluminum oxide nanopowder in the modifier, strongly influencing the structure of the castings, have been chosen. It has been shown that even small admixtures of the modifier (0.07-0.25%) based on aluminum oxide allow refining the casting grain, reducing the average size of lead inclusions and forming a dispersed network of eutectoid inclusions.

Nonmetallic Inclusion Distribution within Ingots for Power Generation Engineering Forgings

Results are provided for a study of the distribution and location of nonmetallic inclusions in large forgings of steel 38KhN3MFA weighing 24.2 and 23.52 tons with a normal configuration and with a changed shape of the bottom part (“convex” bottom) cast in a vacuum. It is shown that the change in ingot bottom section geometry leads to an increase in temperature gradient and as a consequence to an increase solid phase advance intensity. In turn, this leads to more uniform distribution of oxysulfide inclusions. The sulfide inclusion content in the ingots compared increases from the periphery to the ingot axis. Dependences are obtained for metal ductility properties, i.e., relative elongation, relative reduction of area, and impact strength on sulfide inclusions distribution over ingot levels, and their unfavorable effect on these properties is established. It is shown that a reason for the reduction in ductility properties is sulfide phase location in the form of films of dendrite boundaries that occurs under conditions of a shortage of oxygen in the melt. This leads to a reduction in oxysulfide content and formation of a sulfide component in an unfavorable form distributed over cast grain boundaries. The ingots are destined for domestic power generation engineering forgings.

The influence of alloy composition on the as-cast grain structure in near net shape low-density steels

ABSTRACTLow-density steels are considered an attractive potential replacement for conventional steel in industries such as the automotive sector. However, there are several issues that need to be overcome before they become commercially useful grades. A significant constraint is in their processability, for example, a large as-cast grain size means these steels are prone to hot cracking. This paper explores how compositional variations affect the as-cast grain size in 12 low-density steels cast at solidification rates representative of near net shape casting. It is shown that while mushy zone width is a good indicator of the cast grain size, using a mushy zone width from liquidus to 85% solidified fraction gives a better correlation. It was found that the as-cast grain size of a 7 wt-% Al steel can be reduced from 736 to 244 µm through the addition of 1.5 wt-% Si which acts to increase the mushy zone width by 19°C.

Characterization of weld seam properties of extruded magnesium hollow profiles

Extrusions of hollow profiles with weld seams were conducted using the magnesium alloy ME21 applying various extrusion ratios. Subsequent analysis of the profiles’ microstructure was performed comparing weld free with weld seam containing material using (polarized) light optical microscopy (LOM). Additionally, the local texture and microstructure in the weld-free material as well as in the weld seam region has been examined with a scanning electron microscope coupled with electron backscatter diffraction technique (SEM-EBSD). The weld-free material and the weld seam are characterized by recrystallized microstructures, whereas few residual cast grains were identified. The local texture distinctively changes from the weld-free material to the weld seam. The texture of the weld-free material is comparable with the typical ME21 sheet texture. In the weld seam area, a pole density is found, which is distributed towards the transverse direction (TD) combined with a split and broadening of the pole density in the extrusion direction (ED). This texture influences the mechanical anisotropy due to the dependence of the activation of basal 〈a〉-slip and \( \{ 10\bar{1}2\} \;\langle 10\bar{1}1\rangle \)-extension twinning on the loading direction in favorably oriented grains.

Effects of Treatment Duration and Cooling Rate on Pure Aluminum Solidification Upon Pulse Magneto-Oscillation Treatment

The effect of pulse magneto-oscillation (PMO) treatment on casting grain size has been widely investigated. Nevertheless, its mechanism remains unclear, especially when PMO is applied at different periods during solidification, namely when only applied above the melting point. In the present work, the effect of PMO treatment applied at different segments during solidification was investigated. It was found that the dendrite fragmentation model may well explain the effect of PMO applied during the dendrite growth stage. However, only the cavities activation model may account for the effect when PMO is conducted above the melting point. In current study, the effect of PMO treatment on grain size was also investigated at various cooling rates. It was established that the cooling rate had only a slight effect on grain size when PMO treatment was applied. Thus, PMO treatment may provide homogeneous grain size distribution in castings with different wall thicknesses that solidified with various cooling rates.

Физическая химия и физика металлургических систем

Yttrium belongs to the same group as lanthanum, and its chemical properties are close to those of the latter. Therefore, yttrium is referred to as a rare earth metal. When added to a heavily deoxidized metal, yttrium refines a primary cast grain, reduces the area of treeing, purifies grain boundaries of non-ferrous inter-metallic compounds, reduces the size of non-metallic inclusions, and enhances heat resistance and high temperature strength of special steels. Optimal yttrium additive in the metal does not exceed 0.3 to 0.5 wt. %. Complex interaction of yttrium with oxygen in the presence of residual concentrations of aluminum, calcium and magnesium in the metal was not studied at all. Thermodynamic modelling of steel deoxidation using yttrium in the presence of low concentrations of aluminum, calcium or magnesium is developed. The surfaces of component solubility in liquid steel are created for Fe–Y–Al–O–C, Fe–Y–Ca–O–C, and Fe–Y–Mg–O–C systems. To make calculations related to oxide systems, all possible phase equilibria are established, coordination of equilibrium constants dependency on temperature is carried out, and energy parameters of the subregular ionic solution theory are specified. The surfaces of component solubility show that deoxidation by yttrium is a complex process due to the presence of calcium and aluminum in steel. Deoxidation products will contain complex phase compositions of oxides based on CaO, Al 2 O 3 , and Y 2 O 3 . In case of steel deoxidation by yttrium and magnesium, the process is performed alternately. Either yttrium or magnesium acts as a deoxidizer.