Aluminum Solid Solution Research Articles

Effects of Silicon Carbide and Tungsten Carbide in Aluminium Metal Matrix Composites

In the present study, an attempt has been made to synthesis Al6061/SiC/WC hybrid aluminium composites using stir casting method under various mass percentage of reinforcement. The mechanical properties such as compressive strength, tensile strength, hardness and wear resistance have been characterized and investigated. From the micro structural analysis of hybrid composites, it has been observed that reinforcement particles have been uniformly distributed without clustering of particles in matrix alloy. The precipitate of Mg2Si and un-dissolved Al6 (Fe, Mn) in aluminium solid solution has been observed as interfacial reaction. The hardness of hybrid composites has been increased due to incorporation of stiffer and stronger reinforcement in the matrix material. The presence of SiC and WC reinforcement in the matrix alloy can significantly enhance the compressive, tensile strength and wear resistance of aluminum hybrid composite.

Thermodynamic assessment of the Al-Mg-Si-Ti phase diagram for metal matrix composites design

Abstract A thermodynamic assessment of the equilibrium phase composition in the Al-rich side of Al-Mg-Si-Ti quaternary system was carried out using the CALPHAD methodology. The system was described at constant Mg content of 12.5 wt% and in the concentration range up to 10 wt% Si and 5 wt% Ti. In the Al-rich side, no ternary and quaternary phases were detected; binary phases Mg2Si, Al3Ti and β-Al3Mg2 are in equilibrium with the aluminum solid solution. The obtained data can be used to simulate the crystallization processes in the Al-Mg-Si-Ti system and to determine rational temperature-concentration conditions for in-situ metal matrix composites production.

Experimental Investigations on the Failure of Diesel Engine Piston

Piston failure is not a common incidence usually associated with micro-structure aspect. Pin hole or skirt of the piston is affected that most of the failure was initiated by cracks. In this study, investigations of piston failure using experiments have been presented. The average value of the hardness is 61 HRB. Hardness of the surface is clearly differs from the crown to skirt of the piston. The high percentage of silicon, increased the piston life, but could not retain high temperatures during the operating time and finally failed. Copper percentage decreases the mechanical properties of the alloys. The micro-structure of the piston particles like small, angular and primary silicon and Mg2Si particles distributed in a matrix of aluminum solid solution throughout structure.

Superplastic-Like Elongation by Transition of Deformation Mechanism from Grain Boundary Sliding to Solute Drag Creep in Fine-Grained Al-Mg Solid Solution Alloy

It is widely accepted that the dominant deformation mechanism of fine-grained superplasticity is through grain boundary sliding (GBS) that occurs in fine-grained materials. However, it has been reported that in “Class I” solid solution alloys, superplastic-like behavior controlled by trans-granular deformation occurs by solute drag creep. In this study, we have investigated superplastic behavior in a fine-grained aluminum solid solution alloy with a thermally unstable microstructure. To obtain fine-grained microstructure, friction stir processing (FSP) was applied to a commercial 5083 aluminum (Al−Mg) alloy. An equiaxial fine-grained microstructure with a grain size of 7.4 μm was obtained after FSP; however, this microstructure was unstable at high temperatures. Generally, for fine-grained superplasticity or GBS to occur or continue, the fine-grained microstructure must be smaller than 10 μm during high-temperature deformation. However, a large elongation of over 200% was observed at high temperatures despite the occurrence of grain growth. From microstructural observations, it was determined that a fine-grained microstructure is maintained in the early stage of deformation, but at strain levels greater than 100%, trans-granular deformation occurs. The microstructural feature of this trans-granular deformation is similar to the deformation microstructure of solute drag creep observed in “Class I” solid solution alloys. This indicates that a change in the deformation mechanism from GBS to solute drag creep takes place during high-temperature deformation. Here, based on our observations on our model system, which is a thermally unstable aluminum solid solution alloy, we discuss the possibility of a superplastic elongation occurring by means of a transition of the deformation mechanism.

Phase composition and mechanical properties of Al–1.5%Cu–1.5%Mn–0.35%Zr(Fe,Si) wire alloy

By using the experimental study and Thermo-Calc software simulation, the chemical composition of the model alloy containing 1.5% Cu, 1.5% Mn, 0.35% Zr (without the necessity of Sc addition) and with allowable Fe and Si content of up to 0.5% and 0.2%, respectively, have been justified. It was shown that the as-cast structure of the model alloy had the minimum quantity of eutectic inclusions of the Al2Cu and Al15(Fe,Mn)3Si2 phases formed during nonequilibrium solidification, whereas all zirconium content and about 1.1% Mn and 0.8% Cu were dissolved in the aluminium solid solution. Such structure provides high plasticity that allows for the deformation of ingots without their preliminary homogenization. By using the methods of radial-shear rolling (RSR), the 9 mm wire rods were produced from the ingot. The ductility of the rod was sufficient for cold deformation (rolling and drawing) with a high degree of deformation. In particular, a wire with diameters of 1 mm and 0.5 mm, and with UTS value of 430 MPa and 590 MPa, respectively, was obtained by cold drawing. Annealing after drawing reduces the strength properties and improves ductility of the obtained wire. EBSD analysis of the wire after annealing revealed that the described changes in mechanical properties are associated with the formation of a recrystallized grain structure (even in the presence of Zr and Mn-containing dispersoids in a large amount). Thus, using the example of the experimental model alloy, the principal possibility of obtaining a wire with a sufficiently high set of mechanical properties without the necessity of homogenization annealing, solution treatment, and water quenching has been shown.

Structure and Selected Properties of Arc Sprayed Coatings Containing In-Situ Fabricated Fe-Al Intermetallic Phases

The paper presents the results of research on the production by means of arc spraying of composite coatings from the Fe-Al system with participation of in-situ intermetallic phases. The arc spraying process was carried out by simultaneously melting two different electrode wires, aluminum and steel. The aim of the research is to create protective coatings with a composite structure with a significant participation of FexAly as an intermetallic phases reinforcement. The synthesis of intermetallic phases takes place during the (in-situ) spraying process. Currently most coatings involving intermetallic phases are manufactured by different thermal spraying methods using coating materials in the form of prefabricated powders containing intermetallic phases. The obtained results showed the local occurrence of intermetallic phases from the Fe-Al system, and the dominant components of the structure have two phases, aluminum solid solutions in iron and iron in aluminum. The participation of intermetallic phases in the coating is relatively low, but its effect on the properties of the coating material is significant.

Development of the Aluminum Powder Composite Based on the Al–Si–Ni System and Technology of Billet Fabrication of This Composite

Results of an investigation into the development of the composition and fabrication technology of compact billets of the aluminum powder composite material based on the Al–Si–Ni system for space-rocket hardware are presented. The composite production was performed as follows: initially the powder of the matrix alloy is prepared by gas sputtering, and then a mixture of the matrix alloy powder and alloying dispersed additives is subjected to mechanical alloying in high-energy apparatuses. The method of degassing the mechanically alloyed composition in a thin layer (in order to exclude material ejection from a container when degassing a larger volume of powder) and process regimes of composition compaction are developed using the unique equipment available at OAO Kompozit (Korolev, Moscow oblast)—a vacuum press. Using this technology, cylindrical briquettes up to 100 mm in diameter and up to 120 mm in height are fabricated. Newly developed and patented Kompal-301 composite material has substantial advantages over SAS-1-50 power alloy applied for similar purposes. Its thermal linear expansion coefficient is lower by a factor of 1.5, while the precision limit of elasticity is higher by a factor of 2–3 upon similar strength characteristics. The final structure of a compact briquette is a matrix in which dispersed particles of excess silicon are distributed rather uniformly against the background of the aluminum solid solution. Coarser isolated silicon particles are met in separate regions of the structure. Unfortunately, they are the cause of low plasticity of briquettes, which prevents the formation of semifinished products by plastic deformation; however, such low plasticity does not immediately negatively affect the fabrication of the briquettes themselves.

Influence of Annealing at Various Temperatures on the Structure and Hardness of Amorphous Ribbons of the Al85Y8Ni5Co2 Alloy

Aluminum-based metal glasses are a promising new family of materials. However, the influence of thermal treatment on the structure and properties of amorphous alloys of the Al–Y–Ni–Co system is still not studied in detail. In this work, amorphous ribbons of the Al85Y8Ni5Co2 alloy are formed by quenching on a rotating copper disc. The influence of annealing in vacuum at temperatures from 100 to 500°C for 30 min on the structure and hardness of these ribbons is investigated. To investigate the variations occurring in their structure after thermal treatment, scanning electron microscopy, X-ray structural analysis, and differential scanning calorimetry are used. To investigate the influence of annealing on mechanical properties of ribbons, the Vickers microhardness is measured. Conclusions on the variation in hardness depending on the structure of ribbons of the Al85Y8Ni5Co2 alloy are made based on these results. It is established that their microhardness increases with an increase in temperature, reaching the maximal value of 575 ± 7 HV after annealing at 350°C, and then decreases with a further increase in the thermal-treatment temperature. It is shown that ribbons of the Al85Y8Ni5Co2 alloy remain totally amorphous after annealing at t ≤ 250°C for 30 min, and crystalline phases are absent in the structure. An abrupt increase in hardness after annealing at 350°C is associated with the formation of nanocrystals of the aluminum solid solution 10–30 nm in size in an amorphous matrix surrounded by the residual amorphous matrix, while its further decrease is caused by an increase in the size of these crystals and the appearance of Al3Yand Al19Ni5Y3 intermetallic compounds in the structure.

EFFECT OF ANNEALING AT DIFFERENT TEMPERATURES ON THE STRUCTURE AND HARDNESS OF AL85Y8NI5CO2 ALLOY AMORPHOUS STRIPS

Aluminum-based metallic glasses are the new promising family of materials. However, the effect of heat treatment on the structure and properties of Al–Y–Ni–Co amorphous alloys has not been widely studied so far. In this paper, Al85Y8Ni5Co2 amorphous alloy strips were obtained by hardening on a rotary copper wheel. The effect of vacuum annealing at temperatures ranging from 100 to 500 °C for 30 minutes on the structure and hardness of these strips was investigated. Transmission electron microscopy, X-ray diffraction analysis, and differential scanning calorimetry were used to study changes in the structure of strips after heat treatment. Vickers microhardness was measured to investigate the effect of annealing on the mechanical properties of strips. The results obtained allowed for the conclusions made about changes in hardness depending on the Al85Y8Ni5Co2 alloy strip structure. It was found that as the temperature rises, strip microhardness increases reaching a maximum value of 575±7 HV after annealing at 350 °C, then it decreases with a further increase in the annealing temperature. It was shown that the Al85Y8Ni5Co2 alloy strips remain completely amorphous and no crystalline phases are detected in their structures after annealing at temperatures up to 250 °C for 30 minutes. A sharp increase in hardness after annealing at 350 °C is associated with 10–30 nm nanocrystals of an aluminum solid solution formed in the amorphous matrix and surrounded by a residual amorphous matrix, while further hardness decrease is associated with the increasing sizes of these crystals and Al3Y and Al19Ni5Y3 intermetallics formed in the structure.

Mechanism and Kinetics of Formation of Intermetallic Layers on the Surface of Steel Press Molds in Casting of Silumins

Regular features of the mechanism and kinetics of formation of transition layers under interaction between castable silumins and die steel 4KhVMFS (DI-22) used for making press molds are determined. The process of dissolution of the material of the press molds in AL-2 (AK12) silumin is accompanied by formation of aluminum-enriched intermetallic compounds of FeAl3 and Al4Si2Fe types and then by formation of Fe2Al5 and Fe3 Al intermetallic compounds with elevated iron content on the contact surface. Cross diffusion of aluminum is activated in regions under the continuous intermetallic layer on the surface of the mold and causes formation of a layer of a solid solution of aluminum in the steel, which is responsible for sticking of the material of the casting to the mold.

INVESTIGATION OF POSSIBILITY TO PRODUCE HIGH-STRENGTH BORON ALUMINUM SHEETS WITHOUT HOMOGENIZATION AND QUENCHING OPERATIONS

Al–Cu–Mn (Zr) alloys feature high strength and processability without any thermal treatment operations. Al–2%Cu–1,5%Mn–2%B and Al–2%Cu–1,5%Mn–0,4%Zr–2%B alloys were obtained in order to investigate the possibility of producing a aluminum boroncontaining alloy in the form of high-strength sheet rolled stock without thermal treatment. Melting was performed in the RELTEK induction furnace with intense melt stirring to eliminate sedimentation of boride refractory particles. Melting temperature was 950– 1000 °С. Melt was poured into 40×120×200 mm graphite casting molds. Calculation methods (Thermo-Calc) were used to demonstrate that manganese forms complex borides with aluminum and zirconium at a melting temperature while there is enough manganese in liquid and there is practically no zirconium left. Experimental methods (electronic scanning microscopy and electron microprobe analysis) proved the formation of the complex AlB2Mn2 boride, however, manganese remained in a solid solution is enough to form the Al20Cu2Mn3 phase particles in the amount up to 7 wt.%. In the alloy with zirconium, boron stimulates primary Al3Zr crystal separation and, therefore, zirconium content left in the aluminum solid solution is not sufficient for hardening. It is shown that it is possible to produce thin-rolled steel with a thickness of less than 0,3 mm with uniformly distributed clusters of the boride phase with a particle size of less than 10 μm. A high level of strength up to 543 MPa is reached without the use of hardening and aging due to the precipitation of Al20Cu2Mn3 phase dispersions during hot deformation (t =450 °C).

Formation process and properties of aluminium–chromium slag

In order to realize the application of aluminium–chromium slag for economical recycling, its formation process and properties, including the chemical composition and phase composition, physical properties, and microstructure, were studied. The main chemical components of aluminium–chromium slag are Al2O3 and Cr2O3； Cr, CaO, and MgO, among others, are also present as impurities. The main phase is a solid solution of aluminium and chromium oxides; this possesses high refractoriness, good mechanical properties at high temperature, and relative stability in chemical composition. CaO is the main volatile component; variations in the CaO levels affect the thermal conductivity and high-temperature linear thermal expansion, and thus, the mechanical properties of the slag.

The Influence of Boroaluminizing Temperature on Microstructure and Wear Resistance in Low-Carbon Steels

This article investigates the possibility of improving the wear resistance of carbon steel 30 by means of boroaluminizing in treatment pastes. Boroaluminizing was conducted in sodium fluoride (as an activator), boron carbide, and aluminum at furnace heating (the latter two components were taken in a ratio of 4 to 1). The treatment was administered for 4 hours in four temperature modes between 950°C and 1,100°C with a 50°C difference between modes. The microstructure, microhardness, and elemental and phase compositions of the boroaluminized layers were investigated. In addition, the wear resistance of the boroaluminized steels was tested. It was established that treatment temperatures of 1,000°C and lower lead to the formation of layered structures consisting of iron aluminides that are mainly located on top of the diffusion layer and iron borides adjacent to the base metal. Moreover, the use of boroaluminizing temperatures over 1,000°C results in the formation of a heterogeneous structure with iron borides FeB and Fe2B evenly distributed in the matrix of aluminum solid solution in iron. This contributes significantly to the mechanical properties of the layer; in particular, it enhances its wear resistance. It was established that the wear resistance of steel 30 significantly improves after treatment at 1,100°C in comparison with temperature modes of 950°C and 1,000°C.

Investigations Regarding Electron Beam Surface Remelting of Plasma Nitrided Spray‐Formed Hypereutectic Al–Si Alloy

Plasma nitriding of aluminum alloys is a suitable method for improving wear resistance because of the hard ceramic AlN layer formed. However, the surface's load‐bearing behavior is greatly limited by the low hardness of the Al base material. New investigations regarding improved load support of the thin AlN layer examine the treatment sequence of nitriding and subsequent EB remelting. Because of its broad range of beneficial alloying elements (Si, Fe, Cu, Mg), a hypereutectic Al–Si alloy (DISPAL® S232) − made by spray forming − was used as the base material. The electron beam remelting process is carried out on samples with a nitride layer thickness of approx. 3 μm. As a result of the newly formed phases, grain refinement, and oversaturation of the aluminum solid solution, the surface hardness beneath the nitride layer can be increased by up to three times compared to that of the initial base material. The estimated enhancement in load support is evaluated by unlubricated wear tests using a pin‐on‐disc configuration and scratch tests under constant loading conditions. Furthermore, the wear mechanisms are investigated by means of detailed SEM examination of the remelted surface layer.

Isothermal Solidification of an Al–Zn Alloy

In diffusion brazing, a brazing alloy layer thickness introduced into the gap between brazed parts is very small, which hinders the study of the isothermal solidification process. In this work, the isothermal solidification of an Al–Zn alloy is investigated at large volume and mass of the initial liquid that takes part in isothermal solidification. Zinc cylinders are caulked in the holes bored in aluminum cubes. The samples thus assembled are held at 500 ± 10°C for different times. The volume fraction of isothermal solidified crystals has been determined, and the growth rate of isothermal crystals is shown to decrease upon holding. The crystals formed during isothermal solidification width are up to 380 μm and length more than 1 mm. They are observed in the samples that are held more than 2 days. The zinc content in the isothermal solidified crystals corresponds to its mean content in the aluminum solid solution at 490–510°C, according to the Al–Zn phase diagram. The composition of the former liquid that surrounded the crystals during isothermal solidification coincides with the equilibrium composition of the liquid in the Al–Zn system at a temperature of 490–510°C.

Use of Calcium in Alloys: From Modifying to Alloying

Calcium is one of the most widespread and, consequently, low-cost metals on Earth. It has been applied for a long time in modifying and alloying alloys of heavy metals, in particular, lead and copper. It is used as a modifier in cast irons and steels. Calcium began being applied for alloying light alloys based on aluminum and magnesium comparatively recently. In this review, the application fields of metallic calcium and its influence on the structure and properties of various alloys are considered. Alloys based on aluminum–calcium eutectic have been systematically investigated over last few years, and it has been established that they possess casting properties no worse than these of silumins, and they can be hot-rolled and cold-rolled with a high degree of deformation. Ternary and more complex phase diagrams of systems including calcium are constructed and multicomponent alloys based on them are investigated. All these circumstances make it possible to outline several groups of new promising Ca-containing aluminum alloys: (i) alloys hardening without quenching due to the isolation of nanodimensional particles of Al3Zr, Al3Sc, and Al3(Zr,Sc) phases; (ii) high-strength alloys alloyed with traditional hardening elements of the aluminum solid solution, such as zinc and magnesium; and (iii) composite alloys having more than 20% eutectic intermetallic compounds in the structure. All these materials have reduced density, an improved set of operational properties, increased corrosion resistance, and high manufacturability when producing cast and deformed half-finished products.

EFFECT OF SILICON ADDITION ON SPECIFIC ELECTRICAL RESISTIVITY AND HARDNESS OF Al–1%Fe–0,3%Zr ALLOY

Calculation methods and Thermo-Calc software were used to analyze isothermal sections of the Al–Fe–Si–Zr alloy diagram at 450 °C and 600 °C, and polythermal sections at the concentrations of silicon up to 2 wt.% and zirconium up to 1 wt.%. It has been shown that a favorable phase composition consisting of an aluminum solid solution (Al) and an Al8Fe2Si phase with zirconium contained in a solid solution (Al) can be achieved under equilibrium conditions when making a cast section at silicon concentrations of 0,27–0,47 wt.%. In order to implement the process under non-equilibrium conditions of the abovementioned structural components and to ensure Zr inclusion in the (Al) composition, test ingots were made at an increased cooling rate (over 10 K/s). The metallographic analysis of the sample cast structure revealed the desired structure at 0,25 wt.% of Si and 0,3 wt.% of Zr in the alloy. The Al–1%Fe–0,3%Zr–0,5%Si alloy microstructure also contains the (Al) + Al8Fe2Si eutectic, but it is observed that the Al8Fe2Si phase is partially transformed into Al3Fe in step annealing at 600 °C. The structure of the alloy with 0,25 wt.% of silicon in the T600 state contains fragmented particles of the (Al) + Al8Fe2Si degenerate eutectic along the boundaries of dendritic cells. It has been found that the Si : Fe = 1 : 2 ratio in the alloy has a positive effect on its mechanical properties, especially hardness, without any significant conductivity reduction in the annealing process. This effect is explained by compact morphology formation in the structure of Al8Fe2Si phase particles. Moreover, silicon accelerates solid solution decomposition in terms of zirconium, as shown by the experimental graphs of hardness and resistivity dependence on the annealing step. Using the optimization function for the given hardness and resistivity parameters, the Al–1%Fe– 0,3%Zr–0,25%Si alloy demonstrated the best set of properties in the T450 state.

USING CALCIUM IN ALLOYS: FROM MODIFICATION TO ALLOYING

Calcium is one of the most common and, therefore, cheap metals on earth. It has long been used for the modification and alloying of heavy metal alloys, in particular lead and copper. As a modifier, it is used in cast irons and steels. More recently calcium started to be used in light alloys based on aluminum and magnesium. This review covers the applications of metallic calcium, its effect on the structure and properties of various alloys. Over the past few years, systematic studies of aluminum-calcium-eutectic alloys have been carried out and it has been found that their casting properties are no worse than that of silumins, and they can be subjected to hot and cold rolling with a high degree of deformation. Threefold and more complex phase diagrams of systems including calcium were constructed, and multicomponent alloys based on them were investigated. All this allowed us to distinguish several groups of new promising calcium-containing aluminum alloys: (1) alloys hardened without quenching due to nanosized Al3Zr, Al3Sc and Al3(Zr,Sc) phase particles precipitated during annealing; (2) high-strength alloys doped with traditional hardening elements of aluminum solid solution, zinc and magnesium; (3) composite-type alloys containing more than 20% of eutectic intermetallics in their structure. These alloys have a reduced density, an improved set of performance properties, increased corrosion resistance and high manufacturability when making cast and deformed semi-finished products.

Investigation into the Fabrication Possibility of the Boron–Aluminum Sheet Rolling of Increased Strength without Using Homogenization and Quenching

Al–Cu–Mn (Zr) aluminum alloys possess high strength and manufacturability without operations of thermal treatment (TT). In order to investigate the fabrication possibility of the aluminum boron-containing alloy in the form of sheet rolling with an increased strength without TT, Al–2% Cu–1.5% Mn–2% B and Al–2% Cu–1.5% Mn–0.4% Zr–2% B alloys are prepared. To exclude the precipitation of refractory boride particles, smelting is performed in a RELTEK induction furnace providing intense melt stirring. The smelting temperature is 950–1000°C. Pouring is performed into graphite molds 40 × 120 × 200 mm in size. It is established using computational methods (Thermo-Calc) that manganese forms complex borides with aluminum and zirconium at the smelting temperature; herewith, a sufficient amount of manganese remains in liquid, while zirconium is almost absent. The formation of AlB2Mn2 complex boride is proven; however, the amount of manganese remaining in the solid solution is sufficient to form the particles of the Al20Cu2Mn3 phase in amounts of up to 7 wt %. Boron stimulates the isolation of Al3Zr primary crystals in the alloy with zirconium; in connection with this, an amount of zirconium insufficient for hardening remains in the aluminum solid solution. The possibility of fabricating thin-sheet rolling with a thickness smaller than 0.3 mm with homogeneously distributed accumulations of the boride phase with a particle size smaller than 10 μm is shown. A high strength level (up to 543 MPa) is attained without using quenching and aging due to the precipitation of dispersoids of the Al20Cu2Mn3 phase during hot deformation (t = 450°C).

New insights into solidification and phase equilibria in the Al-Al3Zr system: Theoretical and experimental investigations

Phase equilibria and phase transformations during the solidification of alloys in the Al-Al3Zr corner of the Al-Zr system were investigated using both theoretical (DFT and Calphad modelling) and experimental techniques. This work involved two separate teams investigating the phase transformations of alloys of different compositions during solidification at slow cooling rates using DTA, SEM, TEM, XRD, EPMA analysis of as-cast and annealed samples.The formation of eutectic type colonies at the boundaries of dendrites and three types of primary intermetallic phase crystals were detected in the examined samples. A eutectic reaction was implied from the results of a DTA analysis. The obtained results question the currently accepted phase diagram for this part of the system which was based on measurements of the solubility of Zr in the aluminium solid solution and the liquidus surface.