Spray-formed Alloy Research Articles

Microstructural, mechanical, and sliding wear characterization of an Al90Cu4Fe2Cr4 spray-formed alloy

In this work, the microstructure and sliding wear behavior of a spray-formed Al90Cu4Fe2Cr4 (at%) alloy was studied. Mechanical properties under compression and Vickers microhardness were also evaluated. The microstructure of the spray-formed material consisted of an α-Al matrix reinforced with two complex intermetallic phases, λ-Al13Fe4 and Al13Cr2, which are binary based intermetallic structures, with significant amounts of the other elements of the alloy. The dry-sliding wear resistance of the composites was evaluated using a pin-on-disk test configuration, with normal loads ranging from 10 to 20 N and sliding velocities of 0.05–0.2 m.s−1. Alumina spheres were used as counter-bodies in these tests. The samples exhibited a high sliding wear resistance and showed almost no variation in the specific wear rates for all test parameters used, with values ranging from 7×10−4 to 8×10−4 mm3/N.m. The coefficient of friction also remained almost constant, around 0.4, and the main wear mechanism was the delamination of intermetallic particles. The results indicate an improved dry-sliding wear resistance at high normal loads compared to previously fabricated Al-matrix composites reinforced with quasicrystals and complex intermetallic phases. The mechanical properties of this alloy, fabricated in a single-step process, was in the same range as found for previous studies, of Al-matrix reinforced with micron-sized quasicrystals and intermetallics, prepared by more complex processing techniques. The simplicity of the one-step preparation process used in this study contributes to the development of more efficient and cost-effective tribological materials for various applications.

Microstructural features and mechanical properties of spray -formed hypereutectic Al-Si-Ti alloy

ABSTRACT In the present study, the effect of the addition of Ti on the microstructural and mechanical properties of hypereutectic (Al/15 wt. %Si) spray-formed (SF) alloys has been investigated and compared with as-cast (AC) alloys. Al/15Si and Al/15Si/2Ti alloys were synthesised by spray forming method. The microstructural features of the alloys were explored under an optical microscope, and a scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis were carried out for phase identification. The phase analysis confirmed the presence of α-Al and Si phases in all the alloys, with additional peaks attributed to Al3Ti and AlSi2Ti present in the Al/15Si/2Ti alloys. The microstructure of the SF1 alloy (Al/15Si) consisted of globular, fine Si phases (primary and eutectic) distributed homogeneously in the equiaxed Al matrix. The addition of Ti to the binary SF1 alloy led to the formation of an SF2 alloy (Al/15Si/2Ti) with a fine intermetallic phase of Al3Ti and further spheroidisation of Si particles. The SF1 and SF2 alloys exhibited 30% and 40% greater microhardness, respectively, than did their corresponding AC alloys. With the addition of Ti, the ultimate tensile strength of the SF2 alloy increased by 19% compared to that of the SF1 alloy. Furthermore, a significant increase in yield strength and ductility was observed in the SF alloys compared to the AC alloys. Adding Ti to hypereutectic Al/15Si alloy via the spray-forming method provides a better alternative material for aerospace and automotive applications.

Hot compressive deformation behavior and microstructural evolution of the spray-formed 1420 Al–Li alloy

The 1420 Al–Li alloy has been widely used in the aerospace field. To investigate the hot workability of the alloy, a series of hot compression tests were carried out on the spray-formed alloy in the temperature range of 300°C–450 °C with strain rates of 0.0001s−1-10s−1. First, an improved Johnson-Cook model was developed by considering the coupling effect of strain, strain rate, and temperature, and the prediction error of the model was reduced to 5.3 %. Subsequently, processing maps with various strains were established. In addition, the microstructural evolution under various deformation conditions was systematically studied using the electron backscatter diffraction (EBSD) technique. The alloy exhibited uniform deformation under the synergistic effect of the continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) mechanisms. Finally, the feasible hot working windows were identified as 425°C–450°C and 0.01s−1-0.1s−1 based on processing maps and microstructural evolution results. This work could offer comprehensive guidance for the hot working process of 1420 Al–Li alloy from both the macro and the micro aspects.

Hot Compression Deformation Behavior of Spray-Formed AlSn20Cu Alloy

The hot deformation behavior of spray-formed AlSn20Cu alloy during hot compression deformation was studied, and the constitutive equation of AlSn20Cu alloy was established. The samples of spray-formed AlSn20Cu alloy were compressed on Gleeble-3500 thermal simulation test machine. The error of the true stress caused by adiabatic heating effect in the experiment was corrected. The constitutive equation of spray-formed AlSn20Cu alloy could be represented by Zener-Hollomon parameter in a hyperbolic sine function. The results showed that the deformation temperatures and strain rates had a notable effect on the true stress of the alloy. At the identical deformation temperature, the true stress increased with the increase of strain rate. When the strain rate was constant, the stress decreased with the increase of deformation temperature. After hot compression deformation, the tin phase was elongated along the direction perpendicular to the compression axis with short strips and blocks. With the increase of deformation temperature and the decrease of strain rate, Sn phase distribution became more homogeneous.

Study of microstructure and tribological behaviour of spray cast high silicon hypereutectic Al-Si alloy

ABSTRACT This paper presents the study of the microstructure, wear properties of spray-deposited and hot compressed Al-35Si and Al-45Si alloys. The microstructure analysis and wear mechanisms of spray formed and as cast alloys were studied by using optical and scanning electron microscope (SEM). The microstructure of the spray-formed alloys showed fine particulate of primary Si and eutectic phases distributed uniformly in the equiaxed Al- matrix. Microstructural refinement was further increased in the hot-compressed alloys. Hardness, dry friction and wear tests were performed on spray formed alloys and compared with as cast alloys. Friction coefficient (COF) and wear rate of the alloys were measured under different applied loads (10–50 N) and sliding velocities of 1 and 1.5 m/s at constant sliding distance of 5000 m. The results indicated that the hardness and wear resistance of spray formed and hot-pressed alloys were considerably high over that of the as cast alloys. The improvements in hardness and wear resistance of spray-formed alloys were mainly attributed to morphology, size and distribution of Si particles induced during spray deposition process. Analysis of worn surfaces by SEM showed dominant wear mechanism of spray-formed alloy was mainly abrasive wear and oxidation wear.

Microstructure evolution and precipitation characteristics of spray-formed and subsequently extruded 2195 Al-Li alloy plate during solution and aging process

Abstract Al-Li alloys are being successfully employed for manufacturing the structural components of lightweight aircrafts. In this work, the microstructures and precipitation characteristics of the spray-formed and subsequently extruded 2195 Al-Li alloy plate during solid solution and aging treatments were investigated and compared by using different material characterization methods. The grains of the spray-formed alloy were equiaxed without obvious crystallographic textures, whereas in the as-extruded, solution-treated, and aging-treated alloys, the grain morphology changed from being strip shaped near the center of extruded plate to equiaxed near the surface. The grain size increased after the solution treatment, but the aging treatment had no obvious influence on the grain size. A rolling-type texture with a very dominant Brass orientation was observed at the center of the plate, whereas the textures near the surface were rotated, and the crystallographic texture was not sensitive to the solution and aging treatments. The precipitated T1 and θ′ phases, which played a strengthening role in the alloy, gradually formed and developed with increasing aging duration. Besides, the Al-Cu phase in the alloy dissolved and re-precipitated during the heat treatment process, while the Fe-containing particles always remained stable. By applying the uniaxial tension test, a good balance between ultimate tensile strength and elongation was achieved after aging treatment at 170 °C × 6 h.

Microstructure analysis and low-cycle fatigue behavior of spray-formed Al–Li alloy 2195 extruded plate

Microstructure and low-cycle fatigue behavior of spray-formed Al–Li alloy 2195 extruded plate were investigated in this work. The spray-formed alloy after hot extrusion experiment was treated with solid solution treatment and artificial aging. Microstructure analysis indicated the aged plate was dominated by elongated unrecrystallized grains, and had a rolling-type texture along extrusion direction with the highest intensity at Brass component. The existence of T1 phase strengthened the alloy crucially, but δ′ phase was basically absent. Then, the fully-reversed strain-controlled low-cycle fatigue tests were conducted at total strain amplitudes ranging from 0.4% to 1.0% for samples along two orthogonal directions. The stress-strain hysteresis loops were acquired, and the cyclic stress response curves were derived. At low strain amplitudes (0.4–0.5%), the initial cyclic hardening was slight and followed by a cyclic stability, while at higher strain amplitudes (0.6–1.0%), the alloy merely presented a continuously increasing cycle hardening behavior. Moreover, the fatigue life model based on the total strain energy was built and found to be suitable to predict life. Finally, the fatigue fractography observation showed that the fatigue source is relatively concentrated and the fracture surface had typical fatigue striations at 0.5% strain amplitude, while multiple cracks originated on the sample surface and the final fracture zone showed a ductile characteristic at 1.0%. The deformed microstructure near fracture surfaces were observed, and it was found that the cyclic hardening and stability were closely associated with the interaction between moving dislocations and obstacles including (sub)grain boundaries and secondary phase particles against them.

Microstructure and Porous Defects of a Spray-Formed and Hot Worked 7000 Aluminum Alloy

The evolution of microstructure and porous defects of a spray-formed 7000 Aluminum alloy is researched in this paper. The spray-formed alloy is treated by hot isostatic pressing (HIP), homogenization, hot extrusion, solution and aging treatment. Metallographic microscope, scanning electron microscope (SEM) and tensile test are used to research the microstructure and mechanical properties. The results show that, there are two kinds of porous defects in spray-formed alloy, which has gas and no gas. The porous defects of spray-formed ingot can be mostly eliminated by HIP and hot extrusion. After solution and aging treatment, the tensile strength and elongation reach 757MPa and 10.2%, respectively.

Fabrication and microstucture of spray formed powder metallurgy superalloy FGH4095M

Spray forming is a kind of near-net-shaped rapid solidification process based on powder metallurgy gas atomization technology. In this work, the FGH4095M is fabricated by spray forming. The pre-alloy is prepared by vacuum induction melting and vacuum arc remelting techniques. Then the alloy is sprayed by SK2 facility with atomization gas nitrogen at University of Bremen in Germany. In this paper we study the density and microstructure of the spray-formed billet, especially the special morphology of γ’ phase. The results show that density is associated with different parts of the deposited billet. The relative density of the bottom part is higher (99.63%) than those in the other parts. The relative density of top part (98.91%) is lowest. After hot isostatic pressing, the relative density can be up to 100%. Uniform and fine equiaxed grains are the remarkable morphology of spray-formed alloy without prior particle boundary. The sizes of grains are in a range of about l0-40 μm and the grains at bottom part of billet are finest. The grain sizes of primary γ’ phase are in a range of about 0.6-0.8 μm, and the grain sizes of secondary γ’ phase in a range of about 0.1-0.5 μm as well as dispersed spherical tertiary γ’ particles with the sizes of 10-20 nm. The special morphology of secondary γ’ phase occurs with the splitting of γ’ particle, which is related to the low cooling rate of the depositing process. The splitting behavior reduces the total energy of γ’ particle. Total energy of γ’ particle includes elastic interaction energy, elastic strain energy and surface energy, among which the elastic strain energy is invariable. The surface energy increases with the splitting process and the elastic interaction energy reduces. The effect of elastic interaction energy on particles is the major reason why the total energy is reduced. The trend of splitting behavior is analyzed by calculating the equivalent diameter of splitting γ’ particle. It indicates that when the equivalent diameter is over 0.40 μm, there is the possibility to split. Subsequently, spray-formed FGH4095M billet is treated by hot isostatic pressing, isothermal forging and heat treatment process to obtain the FGH4095M alloy turbine disk. The research of tensile property of FGH4095M alloy turbine disk shows an excellent property either at room temperature or at high temperature for the optimized alloy. The relationship between special morphology of γ’ phase and excellent property needs further investigating.

Distribution and Evolution of Porous Defects in Spray Formed 7XXX Aluminum Alloy

Abstract Al-10.8Zn-2.8Mg-1.9Cu-0.16Zr alloy was manufactured by the spray forming technique. Optical microscopy (OM) and field emission scanning electron microscopy (FESEM) were used to investigate microstructures of the spray-formed alloy. Morphology characteristics of all kinds of pores in as-deposited billet were summarized, and their formation mechanism in the alloy was studied. The influences of hot isostatic pressure treatment (HIP) and homogenizing treatment on porous defects in spray formed 7XXX aluminum alloy were studied. The results indicate that the porous defects in the spray-formed alloy are interstices, interlinked pores and gas pores. The distribution and types of porous defects are related with positions of the preform. The main defects in the center of the alloy perform are interstices and gas pores. More interconnected pores are located at the edge of as-deposited billet. The walls inside gas pores are smooth and concave, and the morphology of gas pores remains nearly spherical. Other porous defects show irregular geographies. HIP treatment can get rid of porous defects except for gas pores. Gas pores reappear after heat treatment because they are close pores actually.

Investigation of Porous Defects in Spray Formed 7XXX Aluminum Alloy

In this work, Al-10.8Zn-2.8Mg-1.9Cu alloy was manufactured by the spray forming technique. The microstructure of the spray-formed alloy was investigated by optical microscopy and field emission scanning electron microscopy. The results indicated that the porosity in the spray-deposited alloy was mainly composed of interstices, interconnected pores and gas pores. The distribution and types of porous defects were different, responding to position of the preform.

Ultrafine grain structure features in spray-formed AZ31 magnesium alloy

The ultrafine grain structure was developed in spray-formed AZ31 magnesium alloy by optimizing delivery tube orifice diameter. A significant refinement of grain size ∼1μm in ultrafine level was achieved by using 2.25mm delivery tube orifice diameter. The tensile strength value was increased from 145MPa of as-cast alloy to 250MPa of spray-formed alloy, registering an enhancement of ∼72%. On the other hand, elongation was increased from 6% to 13% using 2.25mm orifice, registering more than onefold increase in elongation. Also, hardness enhancement of ∼49% was observed in spray-formed AZ31 alloy compared to as-cast alloy. The fracture surface of spray-formed AZ31Mg alloy evidences the mixed type of ductile and brittle fracture.

Spray-Formed 50Si-50Al Alloy Deformed in the Semi-Solid State

50Si-50Al alloys were synthesized by the Spray Forming process, and were further deformed in the semi-solid state. The spray-formed microstructure consists of small equiaxed primary Si in 3-5 μm scale. For semi-solid deformation at 650°C at solid fraction (fs) of 0.4, the stress increases initially to reach the peak stress, then decreases to a plateau level, followed by last stage of stress climbing, and the effects of the deformation speeds on the stress level are significant, but not large. For deformation at 750°Cat fs of 0.31, the stress increases initially, then increases at a slower rate, followed by last stage of fast climbing, and the lower the deformation speed is, the higher the deformation stress. The average deformation stress needed at 650 °C was much higher that that needed at 750 °C. The deformation was inhomogeneous at 650°C to become pieces of connected semi-solid clusters, while the deformation was much more homogeneous at 750°C.

Extrusion, Properties, and Failure of Spray-Formed Hypereutectic Al-Si Alloys Based on the Optimization of Fe-Bearing Phase

Based on the densification of the spray-formed hypereutectic Al-Si (hyper-AS) alloys, the microstructural evolution, mechanical properties, as well as the failure are studied in this investigation. The appropriate process and parameters for the densification of the deposits are gained from the thermomechanical simulation. Besides of the spray-formed Al-25Si-5Fe-3Cu (3C) alloy, the microstructures of other spray-formed alloys with Mn/Cr addition are stable without coarsening of the refined α-Al(Fe,TM)Si (TM = Mn/Cr/(Mn+Cr)) particles, which can improve the heat resistance. Especially, a great number of the submicrosized α-Al(Fe,TM)Si phases are observed in the hot-extruded TM-containing alloys. The critical ranges of the major parameter TM/Fe mass ratios that can affect the formation of the α-Al(Fe,TM)Si phases in the cast or spray-formed hyper-AS alloys are severally determined. The structure and lattice constant of the refined α-Al(Fe,TM)Si phases also are characterized. The mechanical properties of the current extruded hyper-AS alloys at room or elevated temperatures are close to or higher than some commercial alloys or other published results. Therefore, the hyper-AS alloys can be proposed as new lightweight, heat-resistant, and high-strength alloys, which can be used in the complex working conditions, such as advanced engine systems. The main reason for the enhanced properties would be the formation of a large quantity of microsized/submicrosized α-Al(Fe,TM)Si phases and abundant dislocations, which can greatly reinforce the matrix and transform the brittle fracture of the needle-like Fe-bearing phases into ductile fracture.

Electron Beam Surface Engineering of Spray-Formed Aluminium-Silicon Alloys

Aluminium alloys are commonly used lightweight construction materials. Spray-formed alloys, in particular, represent a group of materials with very high Si contents and a homogeneous distribution of primary Si and other alloying elements in solid solution and intermetallic compounds. The paper deals with current results of EB surface alloying and dispersing of such alloys using a high frequency beam deflection technique. The results concerning the interactions between the EB and the material and its effects on the layer microstructure, characteristic layer properties as well as detailed researches into friction and wear behaviour and future prospects for the technological transferability to industrial applications will be discussed.

Friction and wear behaviour of electron beam surface treated aluminium alloys AlSi10Mg(Cu) and AlSi35

Abstract Because of their low density, Al based materials are increasingly used for state-of-the-art lightweight construction solutions. With regard to systems subjected to wear, Al alloys cannot be used for highly stressed components, unless they have been made resistant against wear by additional measures such as surface treatment. Electron beam (EB) surface treatment offers a possibility for producing hard wear-resistant layers on components made of Al alloys. Concerning Al materials, distinct improvements of layer properties can be achieved exclusively by the use of liquid phase surface processes (remelting, alloying, dispersing and cladding). The paper deals with current results of investigations in the field of EB surface remelting and alloying technologies of cast alloy AlSi10Mg(Cu) and spray-formed alloy AlSi35. The EB surface treatment of these alloys causes significant changes of properties in surface layers with depths of 0.5–4.0 mm basing on a local modification of microstructure. The hardness and scratch energy density of surface layers are 2–7 times higher than those of the base materials. Moreover, studies on friction and wear behavior under oil lubricated conditions at 80 °C impressively demonstrate the upgraded surface layer properties. Depending on the type of EB-alloying additives (Co, Cu, Ni powder) the specific wear rate decreases by a factor of 10–50 by effectuating a lower coefficient of friction simultaneously. The technologies discussed give a picture of the potential of EB technologies and offer new possibilities for improving service life and reliability of engine components, among others.

Precipitate Behavior and Microstructure Characterization of An Al-Zn-Mg-Cu Alloy Prepared by Spray Forming Process

A high Zn content Al-Zn-Mg-Cu alloy was prepared by spray forming process and the precipitate behavior and microstructure of the extruded alloy were also investigated. The precipitate sequence of the spray-formed alloy could be described as “α-solid solution → GPI zone → GPII zone (also called Metastable ′ )→ Stable  (MgZn2)” during artificial ageing treatment. In the early stage of artificial ageing treatment, the GPI zone was the main strengthening phase and kept coherent relationship with the matrix. With the increasing of ageing time, ′ phase dominate strengthening phase and kept semi-coherent relationship with the matrix. With the further increasing of ageing time,  phase took the place of ′ phase, and dominated the strengthening phase in the alloy. The grain size of the spray deposit is finer than that of cast alloys. The ultimate tensile strength of the alloy is over 810MPa in peak ageing condition.

Effect of (Mn + Cr) addition on the microstructure and thermal stability of spray-formed hypereutectic Al–Si alloys

Microstructures and thermal stability of hypereutectic Al–Si alloys with or without (Mn + Cr) addition, prepared via Spray Forming technique, are studied and compared with traditional cast alloys with same composition, using scanning electron microscopy with energy diffraction spectrum, X-ray diffraction, transmission electron microscopy and differential scanning calorimeter. The results show that the Fe-bearing and primary silicon phases in SF-3C alloy can be refined to less than 10 μm, especially in SF-MC21 alloy the Fe-bearing phase is refined into uniformly distributed α-Al(Fe,Mn,Cr)Si phase particles with sizes smaller than 5–6 μm, contributing to the decrease/elimination of the deleterious effect of needle-like Fe-bearing phases. The results of different heat treatments show SF-MC21 alloy possesses excellent thermal stability than SF-3C alloy which is unstable below 750 K for the coarsening of β-Al 5FeSi phase and formation of Al 7Cu 2Fe phase. The study indicates that both the existence of thermodynamically stable α-Al(Fe,Mn,Cr)Si particles and the increase of solidus temperature of SF-3C alloy induced by adding (2Mn + 1Cr) elements contribute to the high thermal stability of SF-MC21 alloy. Contemporarily, combined the phase reactions or transformation occurred during the melting and solidification processes of both spray-formed hypereutectic Al–Si alloys, the microstructure formation of spray-formed alloys is discussed.

Characterization of silicon phases in spray-formed and extruded hypereutectic Al–Si alloys by image analysis

The silicon phases in the spray-formed and extruded hypereutectic Al–Si alloys (AlSi18, AlSi25 and AlSi35) have been quantitatively evaluated by means of image analysis technique. The influence of silicon content in the alloys, thermal conditions during spray forming of the alloys and hot extrusion of the spray-formed alloys on the size, shape, dispersion and orientation of the silicon phases have been studied and discussed. In general, the silicon phases are greatly refined and uniformly distributed in the spray-formed Al–Si alloys. This improvement in the silicon phases is further facilitated by low thermal input as well as fast cooling conditions during spray forming. The silicon particles in the as-extruded Al–Si alloys appear more homogeneous and regular than those in the as-deposited Al–Si alloys but exhibit a certain amount of anisotropy and a tendency to preferred orientation. The silicon particles, depending on the particle size and shape, may fracture or coarsen during extrusion.

Microstructure Characteristics of Spray-Formed and Melt-Spun Al85Nd5Ni10 and Al89La6Ni5 Bulk Hybrid Composites

The microstructure characteristics of the spray-formed and melt-spun Al85Nd5Ni10 and Al89La6Ni5 alloys were studied. The spray forming process was demonstrated to produce a bulk scale hybrid composite consisting of amorphous and nanostructured phases directly without the need of an amorphous precursor. The spray-formed Al89La6Ni5 deposit (~1 mm in thickness) were partially amorphous, and the amorphous phase came from the undercooled liquid droplets upon deposition. The as-spray-formed Al85Nd5Ni10 deposit (~20 mm in thickness) was completely crystallized due to the devitrification of the retained amorphous phase to nano-scale secondary crystals upon deposition. Primary crystals (~1 μm) are dispersed uniformly in the bulk spray-formed amorphous/or partial amorphous composites and many distinctive deformation twins also are observed in the crystals, however, not twins found in the corresponding completely devitrified ribbon. This is mainly because of the stirring and impacting force offered by high velocity droplets during spray forming and the mismatch of thermal expansion coefficient between primary crystals and adjacent amorphous matrix.