Furnace-cooled Alloys Research Articles

Impact of cooling methods on the corrosion behavior of AA6063 aluminum alloy in a chloride solution

Abstract In this work, the AA6063 Al alloy was processed by cooling at four different conditions. The impact of the type of cooling method on the corrosion behavior of the produced alloys after 1 and 24 h in 3.5% NaCl solutions was carried out. Various electrochemical measurements, such as cyclic potentiodynamic polarization (CPP), chronoamperometric, and electrochemical impedance spectroscopy (EIS) measurements, were employed. The CPP data revealed that the intensity of corrosion of the alloys is highly influenced by the cooling method. The change in the chronoamperometric current at −650 mV (Ag/AgCl) over time indicates the possibility of pitting corrosion, particularly after 24 h, where the recorded currents showed a continuous increase over time. The scanning electron microscopy images taken for the surfaces of the alloys after corrosion confirmed that the lowest deterioration occurring on the surface was for the AA6063 alloy that was quenched in water. The EIS plots also demonstrated that AA6063 alloy exhibits different corrosion resistances when different cooling methods are applied. All measurements indicated that the corrosion resistance increases in the following order: the quenched alloy in water > the air-cooled alloy > the furnace-cooled alloy > the as-received alloy. The exposure for 24 h decreases the corrosion damage of all alloys via the formation and thickening of a top layer of corrosion products on its surface over time.

The Influences of Element Addition on Compression Properties of β-Ti-Mo (Nb)-based Alloys

The influences of the third element addition on the compression properties of Ti-12Mo-based and Ti-33Nb-based alloys was investigated, with emphasis on the influences of element addition on Young’s modulus, superelastic strain and yield strength of water-cooling samples. It is found that the water-cooling Ti-12Mo alloy has a lower modulus, lower yield strength, and higher hyperelastic strain than that of the furnace-cooled alloy of the same composition. Al and Sn can reduce the modulus and the yield strength, and increase the superelastic strain in the above two water-cooling alloys. The decrease in yield strength and modulus is due to orthogonal martensite ɑ’. The enhancement of the superelastic strain originated from the phase transformation of the ɑ”↔βM under stress. The effect of Sn in water-cooling quaternaryTi-18Nb-5Mo-5Sn alloy is different from the above two ternary alloys, and it increases β Phase stability and volume in water-cooling Ti-18Nb-5Mo-5Sn alloy.

Effect of the interspacing of intragranular lamellar LPSO phase on dynamic recrystallization behaviors of Mg-Gd-Y-Zn-Zr alloys

The microstructures with different interspacings of intragranular lamellar long period stacking ordered (LPSO) phase were designed by altering the cooling rate after solid solution heat treatment, and the effect of the interspacing on the dynamic recrystallization (DRX) of Mg-Gd-Y-Zn-Zr alloy was investigated. During hot compression in the temperature range of 350–500 °C and strain rate from 0.001 s−1 to 1 s−1, the water-quenched (WQ) alloy containing closely spaced LPSO lamellae exhibits higher peak stress, larger critical strain, and smaller area fraction of DRX grains than the furnace-cooled (FC) alloy containing widely spaced LPSO lamellae. It is concluded that closely spaced intragranular LPSO lamellae suppress DRX. We further revealed the underlying mechanism using EBSD analyses and TEM characterizations. The larger lamellar LPSO interspacing imposes a much weaker constraint on the activation of the non-basal [c]-containing dislocations, which act as obstacles for the gliding <a > dislocations and hence offer favorable conditions for continuous DRX (CDRX). These findings provide a microstructural guidance for tuning the hot formability of LPSO-containing Mg alloys.

Oxygen addition in biomedical Ti–Nb alloys with low Nb contents: Effect on the microstructure and mechanical properties

Ti–Nb alloys have been widely researched for biomedical applications because of their excellent mechanical properties, corrosion resistance, and superior biocompatibility. In this investigation, the influence of oxygen content on the microstructure and mechanical properties of Ti–Nb alloys with relatively low Nb contents was evaluated. Arc-melted Ti–Nb–O ingots (Nb contents were 15, 17.5, 20, and 22.5 wt% and O contents were 0.15, 0.25, and 0.40 wt%) were hot-rolled and solution-treated at 1200 °C for 1 h, followed by furnace cooling. These samples were characterized by scanning electron microscopy, differential scanning calorimetry, compression tests, and measuring hardness and Young's modulus. The furnace-cooled alloys exhibited typical α + β microstructures, in which the thickness of the α plates decreased with increasing Nb content and increased slightly with increasing oxygen content. A similar behavior was observed for the apparent β-transus, which decreased with increasing Nb content, and increased with increasing oxygen content. The obtained hardness and 0.2% compressive yield stress improved with increasing concentrations of alloying elements. This was due to the solid-solution strengthening promoted by Nb and oxygen, and microstructural refinement induced by Nb addition. The Young's modulus was found to increase very slowly with increasing oxygen content. Owing to the enhancement in yield stress and the small change in elastic modulus with increasing oxygen content, alloys can be designed and produced with high mechanical strength/Young's modulus ratios, favoring their application as biomaterials.

Behavior and mechanism of internal friction peak in quenched Fe-18 at.% Ga alloy

Quenched Fe-18 at.% Ga with high magnetostrictive properties has a peak (Pwq) in temperature-dependent internal friction (IF) spectrum near 320 °C, which disappears for both as-cast and furnace-cooled alloys. However, the mechanism of this peak is not well understood. In this investigation, the behavior and mechanism of this peak were systematically studied. It is found that the Pwq appears when the sample is quenched from a temperature higher than the critical temperature of the order-disorder phase transition and disappears when annealed at 300 °C for 1 h. The Pwq becomes gradually more apparent as the Ga content increases from below ~18 at.%, and the Pwq almost disappears when the Ga content equals 23 at%. Combined with deformation and XRD studies, the Pwq does not originate from the vacancies and dislocations produced by the high-temperature quenching process or a phase transition from D03 to L12, and potential formation mechanisms for the Pwq may originate from the transition of Ga-rich Guinier-Preston (GP) zones to D03 structures or lattice relaxation related to Ga-rich GP zones.

Static softening behavior and modeling of an Al–Cu–Mg–Zr alloy with various pre-precipitation microstructures during multistage hot deformation

The complex precipitates have been found to work on the hot workability of heat treatable Al alloys considerably. In this work, to include the functions of interrupted holding following multistage hot working, double-stage hot compression tests were performed on an Al–Cu–Mg–Zr alloy with different pre-precipitation microstructures which were tailored through air cooling, water quenching and furnace cooling after solution heat treatment. Microstructural characterizations and physically-based modeling were employed to investigate the static softening behaviors during interval holding. The results indicated that static softening fraction increased with rising deformation temperature, strain rate and holding time. Under the same deformation conditions, the furnace-cooled alloy presented the highest static softening, while the lowest in water-quenched alloy. Particularly, double plateaus were presented in the static softening curve of water-quenched alloy when deformed at 300 °C and 0.1 s−1, which was interpreted by static recovery, static precipitation and its coarsening as well as the complete depletion of stored strain energy during post-deformation holding. When deformed at 450 °C and 0.1 s−1, higher static softening fraction and longer plateaus were observed in all alloy specimens due to the remarkable static recovery within a very short holding time after first-pass deformation. In addition, the established recovery model could generally rationalize the experimental results, and the direct static softening contribution of precipitates coarsening was indicated to be slight according to the results of integrated model.

Effects of cooling rate on casting ternary Al–Cu-Sc alloy prepared by ultrasound-assisted molten salt electrolysis

Abstracts The effects of cooling rate on the preparation of casting Al–Cu-Sc ternary alloys by ultrasound-assisted molten salt electrolysis (US-MSE) have been investigated in this work. Increasing cooling rate can strongly refine the microstructures and improve the mechanical properties of the prepared alloy. The average grain diameter and secondary dendrite arm space (SDAS) of the quenched alloy are approximately 198 μm and 4.84 μm, and the values are reduced by 71% and 50% compared to the furnace-cooled alloy. The yield strength (σ0.2) values of the US-MSE alloys are ~ 115 MPa, 148 MPa and 167 MPa (corresponding to cooling rates, 0.1 K/s, 4 K/s and 30 K/s, respectively). There is a competitive relationship among the precipitations of the W (Al, Cu, Sc)-phase, Al3Sc and θ-Al2Cu. Regarding such competitive relationship, the microstructure modifications are found to be paralleled with the improvement in compressive property of the alloy. It should be mainly attributed to the decrease of SDAS, the significant reduction of bulky W-phase and the dispersive Al3Sc induced by ultrasound, which can be preserved by using a fast cooling rate.

Formation of diverse B2+O structure and hardness of Mo-modified Ti-22Al-25Nb alloys upon cooling

Mo-modified Ti-22Al-25Nb alloys are sintered at 900 °C, 1000 °C, 1070 °C, and 1150 °C, followed by quenching and furnace cooling, respectively. We made comparisons of phase composition and microstructure between quenched and furnace-cooled alloys to interpret the phase transformation and microstructure evolution during cooling. The phase transformation was B2→O for the alloy cooled from B2+O region, and was B2→B2+O for those cooled from α2+B2+O, α2+B2, and B2 phase regions. Moreover, the morphology was B2+O colonies for those cooled from B2+O and α2+B2+O phase regions, and was Widmanstätten structure for those cooled from α2+B2, and B2 phase regions. Kinetics analysis indicated that the activation energy for the phase transformation of α2→B2 was 170 kJ mol−1 for Ti-22Al-25Nb, while it was 330 kJ mol−1 for Mo-modified Ti-22Al-25Nb. The retarded phase transformation in Mo-modified Ti-22Al-25Nb further led to curvy Widmanstätten structure when the alloy was furnace-cooled from single B2 phase region. The hardness of the Mo-modified Ti-22Al-25Nb alloys is up to 488 HV, while that of the Ti-22Al-25Nb alloys without Mo addition is less than 400 HV.

Revealing the influence of pre-precipitation microstructure on hot workability in an Al-Cu-Mg-Zr alloy

Hot workability, which indicates the ability of metallic materials to be deformed at elevated temperatures, is generally governed by the microstructure-dependent strength and ductility. In this work, the influence of three types of pre-precipitation microstructure, tailored through different cooling conditions (i.e., air cooling, water quenching and furnace cooling) after heat treatment, on hot workability in an Al-Cu-Mg-Zr alloy was studied by means of constitutive analysis, processing maps and microstructure characterizations using scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. The results showed that pre-precipitation microstructure had a considerable influence on flow stress, hot deformation activation energy, dynamic softening and hot workability. The highest flow stress accompanied by a more notable dynamic softening was shown in the water-quenched alloy, whereas the flow stress in the furnace-cooled alloy was the lowest. The flow stresses of air-cooled, water-quenched and furnace-cooled alloys could be described well by the hyperbolic sine equation with hot deformation activation energies of 180.5, 298.9 and 161.5 kJ/mol, respectively. Dynamic softening mechanisms were found to be associated with different contributions of dynamic recovery, dynamic precipitation and/or dynamic recrystallization in various tempers of the present alloy. Further, the air-cooled alloy showed minimal instability regimes and an optimal pre-precipitation microstructure for hot forming. The deteriorated hot workability in the water-quenched alloy was attributed to dynamic precipitation effects. However, coarse constituent phases in the furnace-cooled alloy were easily broken during deformation under a higher strain rate, which led to deformation instability.

Dual structure O + B2 for enhancement of hardness in furnace-cooled Ti2AlNb-based alloys by powder metallurgy

Powder metallurgic Ti2AlNb alloys were sintered at 900°C, 990°C, 1060°C, and 1100°C (i.e. in the O+B2, α2+B2+O, α2+B2, and B2 phase region, respectively) for 12h, followed by water quenching and furnace cooling. Quenching was employed to reserve the high-temperature phase and microstructure, and furnace cooling aimed to regulate the room-temperature microstructure for the enhancement of hardness. Widmanstatten B2+O structure, which contributes to the properties, was induced from B2 crystals by sintering, unless the alloy was treated in the α2+B2 phase region. With the elevation of the sintering temperature, the content of α2 phase became lower in the furnace-cooled alloys, and the hardness was improved accordingly. The highest hardness performance, 389±23HV, was obtained in the alloy solution treated in the single B2 region, and the alloy was comprised of complete O+B2 Widmanstatten structure.

On the Impact Properties and Fractography of Al–11%Si Casting Alloy

This study focused on investigating the effects of Sr-modification and solidification rate as well as the aging treatment conditions on the impact toughness behavior of Al–11%Si near-eutectic alloys with the objective of fully evaluating its behavior under high rates of loading. The Al–11%Si-based alloys, however, display lower impact energy values than those obtained for hypoeutectic 356 and 319 alloys. The impact behavior of aged Al–11%Si-based alloys is similar under both low and high solidification rate conditions; the air-cooled alloys (high solidification rate), however, display higher impact energy values than do furnace-cooled alloys (low solidification rate). Artificial aging at 240 °C for 44 h produces a significant improvement in the impact energy values as a result of softening effect, regardless of alloy composition. The presence of undissolved intermetallic phases, mainly Al2Cu and α-Al15(Mn,Fe)3Si2, increases alloy brittleness and thus also reduces alloy toughness. The segregation of Al2Cu caused by Sr addition is a further parameter to be considered, especially for furnace-cooled alloys. The impact energy values of air-cooled alloys are significantly higher than those obtained for furnace-cooled alloys based on the microstructural differences between the two categories of alloys, regardless of alloy conditions. Crack propagation occurs mainly in the near-eutectic alloys by passing through the Al2Cu and/or α-iron intermetallic phases, shattering them into fragments. In numerous cases, the morphology of the intermetallic phase is retained, indicating that the fracture is of the transverse type rather than a particle/matrix fracture.

Effect of cooling rate during solution heat treatment on the microstructure and mechanical properties of SP-700 titanium alloys

The relationship between the microstructures and the mechanical properties of solution-treated SP-700 titanium alloys, as obtained with different cooling rates, was investigated. The results indicate that the water-quenched alloy contains the primary α (α_p), α〞-martensite and residual β (β_r) phases. Aging heat treatment can convert both α〞-martensite and the βr phases to the fine-grained α+β equilibrium phases, resulting in a significant increase in tensile strength and hardness. Both the air-cooled and furnace-cooled alloys consist of the α_p, α and β phases. The air-cooled alloy containing the fine-grained α phase has relatively higher hardness. Aging heat treatment causes only a slight enhancement in tensile properties because it cannot convert the phases in both alloys. Stress-induced martensitic phase transformation occurs in the water-quenched alloy under applied stress, after which the alloy exhibits higher tensile strength, higher ductility, and lower yield strength.

Effect of cooling rate on damping capacity of Fe–Cr based ferromagnetic metal alloy

The Fe–15Cr–3Mo–0.5Si alloy was treated by furnace cooling, air cooling or water cooling after annealing at 1100°C for 1h in vacuum atmosphere. The damping performance of the as-treated alloys was tested with dynamic mechanical thermal analyzer and the effects of different cooling rates on phase, microstructure, coercive force and damping capacity were investigated. The results show that the cooling rates have no influence on the crystalline phase and grain sizes of the Fe–15Cr–3Mo–0.5Si alloy. The phase of the as-treated alloys is a single α-Fe. Moreover, Cr- and Mo-containing carbide precipitation is detected on alloy grain boundary of the furnace-cooled alloy, while no precipitated phase on the alloy grain boundary of the air-cooled and water-cooled alloy. In addition, the furnace-cooled alloy shows the smallest coercive force comparing with the air-cooled alloy, and the water-cooled alloy shows the biggest coercive force. The peak values of logarithmic decrement δ of furnace-cooled, air-cooled and water-cooled alloy are 0.209, 0.188 and 0.175 respectively. The gradual decrease of the damping capacity with increasing cooling rate for the alloy mainly lies in the discrepancy of their micro internal stress.

Effects of aging on microstructure evolution and mechanical properties of high-temperature Zn-4Al-3Mg solder

Purpose – This paper aims to investigate the transformations during aging at 200°C for different periods on microstructure and mechanical properties of high-temperature Zn-4Al-3Mg solders. Design/methodology/approach – The solder was melted in a resistance furnace, and different cooling rates were obtained by changing the cooling medium. Subsequently, all the specimens were aged at 200°C for 20 h and 50 h. A scanning electron microscope equipped with an energy dispersive X-ray detector and X-ray diffraction were used for the observation of microstructures and the determination of phase composition. Tensile tests and Rockwell hardness tests were also performed. Findings – After aging, Zn atoms precipitated from the supersaturated α-Al and the (α-Al + η-Zn)eutectoid phase with the original fine lamellar structure coarsened and spheroidized to minimize the system energy. Among these solders, the furnace-cooled alloys exhibited the highest thermal stability, largely retaining their original morphology after aging, whereas the collapse and spheroidization of the η-Zn phase and the coarsening of the η-Zn dendrites took place in the air-cooled and water-cooled samples, respectively. Furthermore, a decrease in tensile strength during aging was attributed to the thermal softening effect. The variation of macro-hardness was mainly associated with the microstructural alterations in terms of quantity, morphology and distribution of soft η-Zn phase and hard intermetallic compounds induced by the aging treatment. Originality/value – The structural stability of eutectic Zn-4Al-3Mg solders solidified at different cooling rates and the effect of aging on mechanical properties were investigated.

Preparation of high-strength Al-Mg-Si-Cu-Fe alloy via heat treatment and rolling

Abstract An Al-Mg-Si-Cu-Fe alloy was solid-solution treated at 560°C for 3 h and then cooled by water quenching or furnace cooling. The alloy samples which underwent cooling by these two methods were rolled at different temperatures. The microstructure and mechanical properties of the rolled alloys were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, and tensile testing. For the water-quenched alloys, the peak tensile strength and elongation occurred at a rolling temperature of 180°C. For the furnace-cooled alloys, the tensile strength decreased initially, until the rolling temperature of 420°C, and then increased; the elongation increased consistently with increasing rolling temperature. The effects of grain boundary hardening and dislocation hardening on the mechanical properties of these rolled alloys decreased with increases in rolling temperature. The mechanical properties of the 180°C rolling water-quenched alloy were also improved by the presence of β″ phase. Above 420°C, the effect of solid-solution hardening on the mechanical properties of the rolled alloys increased with increases in rolling temperature.

Hydrogen generation using the corrosion of Al-Sn and Al-Si alloys in an alkaline solution

We investigated the effects of adding Sn and Si to Al alloys on the corrosion of the alloys and the generation of hydrogen from an alkaline solution using the alloys. With increasing Sn content of up to 20 wt% in the Al-Sn alloy, the volume fraction of the Sn phase as a cathodic site at grain boundaries increased, and consequently, the hydrogen generation rate from an alkaline solution by the alloy also increased. In addition, the quenched Al-Sn alloys had smaller grain sizes compared to the furnace-cooled alloys, and accordingly, exhibited a slightly higher hydrogen generation rate. A galvanic cell was formed between the Al grain and the Sn phase of the grain boundary, and accordingly, intergranular type corrosion was observed on the Al-Sn alloys. Compared with the Al-Sn alloys, a more uniform type corrosion was observed on the Al-Si alloys because the nobler Si was uniformly distributed in the eutectic region formed between the primary Al grains. The hydrogen generation rate increased with an increasing Si content up to 10 wt% and was greater for the furnace-cooled samples than that for the quenched samples due to the more clearly formed eutectic structure.

Effects of post-aging cooling condition on structure and tensile properties of aged Ti–7.5Mo alloy

The present study investigated the effects of post-aging cooling condition on tensile properties of an aged Ti–7.5 wt% Mo alloy. Experimental results indicated that the solution-treated (ST) Ti–7.5Mo samples were comprised substantially of α″ phase, while all aged samples demonstrated the co-existence of α′ and β phases therein. The relative amount of β phase retained in the aged alloy was found sensitive to post-aging cooling condition. Water-quenched (WQ) alloy had the highest β phase content, while furnace-cooled (FC) alloy had the lowest β phase content. The Mo concentration in β phase was also sensitive to post-aging cooling condition. The average Mo concentration in β phase was found highest in FC samples and lowest in WQ samples. Compared to ST samples, all aged samples demonstrated significant increases in yield strength and modulus values, along with decreases in elongation. The effect of post-aging cooling condition on microhardness was similar to that on strength.

Effects of heat treatments on the structure and mechanical properties of Zr–30Ti alloys

In this research the effects of various heat treatments on the structure and mechanical properties of a Zr–30Ti alloy (in wt.%) were examined. A β solution treatment at 1100 °C/10 min was applied, after which the specimens were subjected to water quenching, air cooling or liquid-nitrogen quenching. Some of the specimens were heated in a vacuum furnace at 900 °C for 60 min and subsequently furnace-cooled. The experimental results indicated that these alloys obviously had different structures and mechanical properties when subjected to different heat treatment conditions. The as-cast Zr–30Ti alloys were comprised entirely of a β phase; whereas, the furnace-cooled specimens were dominated by equilibrium α phase. The ω phase was observed in furnace-cooled and air-cooled alloys, especially in the furnace-cooled alloy having the largest quantity of ω phase. It is noteworthy that the water-quenched Zr–30Ti alloy in β + α phase exhibited the highest bending strength/modulus ratios, some as large as 20. Moreover, the elastic recovery capability of the water-quenched alloy (20.4°) was much greater than that of the as-cast Zr–30Ti (9.8°). In the current search for better implant materials, the Zr–30Ti alloy treated by water quenching appears to be a promising candidate due to its low modulus, ductile property, excellent elastic recovery capability and reasonably high strength.

Influence of aging treatments and alloying additives on the hardness of Al–11Si–2.5Cu–Mg alloys

This study investigated the effects of cooling rate, heat treatment as well as additions of Mn and Sr on hardness and hardening characteristics in Al–11Si–2.5Cu–Mg alloys. The results of scanning electron microscopy reveal that the age-hardening behaviour is related to the precipitation sequence of alloy. An energy dispersive spectroscopy analysis was used to identify the precipitated phases. The results also show that the hardness of the solution heat-treated samples is higher in air-cooled alloys than in furnace-cooled ones. Furthermore, the hardness observed in solution heat-treated samples is higher than in as-cast samples for air-cooled alloys, with the highest hardness level in the non-modified alloys. The highest hardness levels among the artificially aged samples were observed in the non-modified, air-cooled alloys. These levels occur after aging for longer times at lower temperatures ( e.g. 30 h at 155 °C). The alloys studied did not display any softening after 44 h at 155 °C, whereas at 180 °C, softening was noted to occur after 10–15 h. At short aging times of 5–10 h, high hardness values may be obtained by aging at 180 °C. At aging temperatures of 200 °C, 220 °C and 240 °C, softening began after 2 h had elapsed. The cooling rate during solidification does not appear to have any significant effect on the precipitation characteristics and hardness of the Sr-modified alloys at certain aging temperatures. On the other hand, the effects of cooling rate may be clearly observed in the non-modified alloys. Manganese has a minimal effect on the hardness of the aged samples as it diminishes the potential action of age-hardening, while strontium lessens the hardness of the artificially aged samples. The effect of strontium, however, is more pronounced in the air-cooled alloys than in the furnace-cooled alloys. Strontium also has a noticeable effect on the reduction of hardness in aged Mg-containing Al–Si–Cu alloys, in that it affects the precipitates containing Cu and Mg.

Influence of cooling rate after homogenization on the flow behavior of aluminum alloy 7050 under hot compression

The influence of cooling rate after homogenization on the flow behavior of aluminum alloy 7050 was investigated by hot compression testing over a range of temperatures, 300–450°C, with strain rates of 0.001–1s−1. It was found that water-quenched alloy exhibited higher flow stresses than furnace-cooled alloy, and the difference in the peak stress decreased with temperature increasing. The strain-hardening rate during the initial stage of hot deformation was higher for water-quenched alloy than furnace-cooled alloy. During deformation at low temperatures with the lowest strain rate, flow softening was observed for both alloys, but this effect was more significant for the water-quenched alloy. The activation energy of the water-quenched alloy was more than twice higher than that of the furnace-cooled alloy. With strain increasing, the activation energy decreased for both alloys. These phenomena were explained based on dynamic precipitation and coarsening during hot deformation according to microstructure examination.