Search

This communication demonstrates the efficacy of heat treatment on the improved deposition characteristics of aluminum alloy powders. A novel furnace was constructed for solutionizing of feedstock powders in an inert atmosphere while avoiding sintering. This furnace design achieved sufficiently high cooling rates to limit re-precipitation during powder cooling. Microscopy showed homogenization of the powder particle microstructures after heat treatment. Cold spray deposition efficiency with heat-treated powders substantially increased for the alloys AA2024, AA6061, and AA7075. [ABSTRACT FROM AUTHOR]

The effect of thermomechanical processing on microstructure, texture evolution, and mechanical properties of Al-Mg-Si-Cu alloys with different Zn contents was studied by mechanical properties, microstructure, and texture characterization in the present study. The results show that thermomechanical processing has a significant influence on the evolution of microstructure and texture and on the final mechanical properties, independently of Zn contents. Compared with the T4P-treated (first preaged at 353 K (80 °C) for 12 hours and then naturally aged for 14 days) sheets with high final cold rolling reduction, the T4P-treated sheets with low final cold rolling reduction possess almost identical strength and elongation and higher average r values. Compared with the intermediate annealed sheets with high final cold rolling reduction, the intermediate annealed sheets with low final cold rolling reduction contain a higher number of particles with a smaller size. After solution treatment, in contrast to the sheets with high final cold rolling reduction, the sheets with low final cold rolling reduction possess finer grain structure and tend to form a weaker recrystallization texture. The recrystallization texture may be affected by particle distribution, grain size, and final cold rolling texture. Finally, the visco-plastic self-consistent (VPSC) model was used to predict r values. [ABSTRACT FROM AUTHOR]

Steel has been the material of choice for automobile manufacturers. In the recent years material such as aluminium and its alloys are taking over the market because of their light weight. The use of aluminium, in automobile manufacturing can result in overall fuel efficiency. Spot welding aluminium alloys require higher electric power and less welding time as compared to steel. Welding guns that can produce an electric current which is approximately 2 to 3 times higher, as compared to steel are required for spot welding aluminium. An efficient method of spot welding Aluminium alloys with the preheating process has been proposed in this paper. Preheating Aluminium sheet before spot welding reduces the thermal and electrical resistance which brings down the electric current requirement to spot weld Aluminium structures. Both spot welding and induction preheating process have been modelled in this paper. The test results of the preheating process have also been verified with practical heating trials. The preheating is performed on-the-fly in advance to spot welding process. The results show that spot welding Al 6082 after preheating up to 200°C, the output current requirements to make the spot weld are reduced by 22%. [ABSTRACT FROM AUTHOR]

The present study is focused on improving metallurgical characteristics and mechanical properties of 6061-T6 aluminium alloy sheet butt welds obtained by common single pass CO2 laser by refining the microstructure with extra laser pass/remelting. Screening experiments were performed initially to enumerate the power density requirement for proper coupling of the laser with the material to develop a defect free weld zone. Recognized process window (3.0 kW power, 3 m/min welding speed for single pass, 2.5 kW power, 6 m/min welding speed for double pass and 18 l/min He flow rate for both) obtained from initial trial was used in butt welding experiment and the weld zones were characterized by macro and microscopic observations, microhardness study and tensile test. The microstructure reveals macro-porosity and crack free welds. The hardness data confirmed presence of heat affected zone (HAZ) and drop in overall hardness in the HAZ of both single and double pass welds. The tensile behaviour shows a decrease in tensile strength and formability as compared to the base material which is attributed to the presence of micro porosity in the single and double pass welds. The fatigue life of the double pass welds was marginally higher compared to the base material and single pass welds. The potentiodynamic corrosion tests showed least resistance to corrosion of single pass weld in a 3.56 wt.% NaCl solution due to the presence of defects in the microstructure and unfavourable residual stress values. [ABSTRACT FROM AUTHOR]

Powder mixture of pure Al and oxidized SiC was consolidated into SiCp/Al composites by equal channel angular pressing and torsion (ECAP-T). The influences of several parameters on the thermal expansions, the thermal conductivities, and the recrystallization temperatures of the as-consolidated composites were studied. These parameters are the number of ECAP-T passes (1, 2, and 4), the content of SiC (10, 20, and 40 wt.%), and the fabrication temperature (150, 250, and 350 °C). The results show that increasing the number of ECAP-T passes has a positive effect on depressing the coefficient of thermal expansion (CTE) of the composite within a certain temperature range, since the total variation amplitude of the CTE is enlarged. The CTE can also be decreased by increasing the content of SiC. The number of ECAP-T passes and the contents of SiC in the composites are both positively related with the thermal conductivity of the composites. No direct relationship between the fabrication temperature and the thermal properties was detected. However, the composite fabricated at too low temperature (150 °C) can not obtain full densification, leading to the appearance of low CTE and thermal conductivity. Finally, when the number of ECAP-T passes is elevated from 2 to 4, the recrystallization temperature of the composite has an obvious declination. [ABSTRACT FROM AUTHOR]

The evolution of the strengthening precipitate in a precipitation-hardening alloy, such as the gamma prime ( γ′) phase in Ni-base superalloys, during heat treating and welding can affect the resultant mechanical properties significantly. Computational kinetics simulation can be a useful tool for understanding and controlling of such evolution. The present study was conducted to simulate the γ′ precipitation and dissolution during aging and welding of the recently developed Ni-base superalloy 718plus using the PanPrecipitation module of the Pandat software along with available thermodynamic and kinetic databases. The purpose was to demonstrate the application of such software and databases to materials processing including heat treating and welding. The variations in the volume fraction, average precipitation size, and number density of γ′ with time during aging and welding were calculated. The calculated results under aging condition agreed well with the available experimental data, while those under welding also predicted the correct trend. [ABSTRACT FROM AUTHOR]

Magnesium alloys are attracting great interest from the automotive industry because of the potential for weight reduction. An AZ91D cast alloy was studied in the current work to understand the effect of heat treatment on the microstructure and dynamic compressive properties. The selected heat treatments include solution treatment (T4) and solution treatment followed by aging (T6). The as-cast alloy microstructure consists of intermetallic β-phase (MgAl) precipitates surrounded by α + β lamellar eutectic in α-Mg solid solution. The AZ91D-T4 specimens showed small β-phase precipitates along the grain boundaries and regions of eutectic mixture. The T6 heat treatment causes the β-phase platelets in the α + β eutectic to grow and develop into β-precipitates. The difference in the phase morphology reflects into the mechanical properties. The Vickers hardness of the T6 heat-treated specimens was 3.6% higher than the as-cast alloy. The compressive yield strengths of T4 and T6 treated specimens were 1.3% and 43.1% higher than those of as-cast specimens. The high strain rate compression testing resulted in increase in the strength with strain rate for the T4 and T6 specimens. A maximum increase of 42% was observed in T6 specimen tested at a strain rate of 4,000/s in comparison to the quasi-static compression. Under high strain rate compression testing, the T6 heat-treated specimens showed failure of the β-precipitates resulting in increased energy absorption in comparison to the quasi-static compression. [ABSTRACT FROM AUTHOR]

Abstract: The exfoliation corrosion (EFC) susceptibility of several 7000 Aluminium alloys has been studied after a variety of heat treatments using two independent corrosion tests (standard EXCO test and an electrochemical test based on potential transients analysis), together with detailed microstructural examinations. It is proposed that depending on heat treatment EFC may occur via two different mechanisms: inter-granular dissolution induced damage (IDD) or inter-granular fracture induced damage (IFD). The coexistence of these two mechanisms, leading to EFC, and their relative predominance explain the influence of alloy composition and heat treatment on EFC susceptibility via the confrontation of the two corrosion tests. [Copyright &y& Elsevier]

Abstract: A protective surface alloy coating on steel surfaces can prevent steels from the heavy LBE corrosion in the LBE cooled reactor. Especially, Fe–Al alloy coating on a steel surface is effective for corrosion resistance in LBE due to the self-healing of a thin and stable Al oxide layer on the surface of the coating layer. In order to investigate the utility of the coating layer under the stress due to the hydrodynamic and thermal stress induced in the practical system. The Fe–Al coated 316SS, which was heat-treated after the coating process, was immersed in the stagnant LBE at 650 °C for 250 h with loading to investigate the corrosion behavior of the specimen with the bending stress. The Fe–Al coating layer was not corroded because of the protection by Al oxide scale which was formed on the surface of the coating layer and the interface between the coating and the matrix during the heat treatment process. The coating layer cracked elastically. The LBE penetrated into the cracks and corroded the 316SS matrix and the pre-coating layer. The matrix exhibited the dissolution corrosion caused by the preferential dissolution of Ni and the oxidation forming the Fe oxide and Cr oxide. The coating layer is effective to reduce the surface of the matrix to be corroded by LBE, and can moderate the corrosion of the depth direction. [Copyright &y& Elsevier]

Tool wear, formed in cutting tool during machining processes, affects the surface roughness of the work piece, cutting forces and other output parameters. The effects of the machining parameters cutting speed (Vc) and the feed rate (f) on built-up edge (BUE), built-up layer (BUL), main cutting force (Fc), and surface roughness (Ra) is investigated in this study. The effects of the cutting parameters on cutting force and surface roughness has been examined by the use of Variance Analysis (ANOVA); and their optimum and critical cutting parameters were determined accordingly. AA2014 aluminum alloy was machined with uncoated carbide tools using Computer Numerical Control (CNC) turning machine under dry cutting conditions. Four different cutting speeds (200 m/min, 300 m/min, 400 m/min, and 500 m/min), five different feed rates (0.10 mm/rev, 0.15 mm/rev, 0.20 mm/rev, 0.25 mm/rev, and 0.30 mm/rev) and a constant depth of cut were selected as the machining parameters. BUE and BUL in the cutting tool were formed most at cutting speed 200 m/min and feed rate 0.30 mm/rev. The lowest cutting force was determined as 137 N at cutting speed 500 m/min and feed rate 0.10 mm/rev. The lowest average surface roughness, however, was determined as 0.93 μm at 500 m/min cutting speed and feed rate 0.10 mm/rev. [ABSTRACT FROM AUTHOR]

Alloying additions of Sc and Zr raise the yield strength of Al-Mg alloys significantly. We have studied the effects of Sc and Zr on the grain refinement and recrystallization resistance of Al-Mg alloys with the aid of computational alloy thermodynamics. The grain refinement potential has been assessed by Scheil–Gulliver simulations of solidification paths, while the recrystallization resistance (Zener drag) has been assessed by calculation of the precipitation driving forces of the Al3Sc and Al3Zr intermetallics. Microstructural performance indices have been derived, used to rank several alloy composition variants, and finally select the variant with the best combination of grain refinement and recrystallization resistance. The method can be used, with certain limitations, for a thermodynamics-based design of Al-Mg and other alloy compositions. [ABSTRACT FROM AUTHOR]

Abstract: A study of the effect of lithium content (1, 3 and 5wt.%) and heat treatment (400°C during 144h) on the corrosion behavior of Ni3Al alloy has been carried out in a 62mol.%Li2CO3–38mol.%K2CO3 mixture at 650°C using electrochemical techniques. Employed electrochemical techniques included potentiodynamic polarization curves, linear polarization resistance, LPR, electrochemical impedance spectroscopy, EIS, and electrochemical noise, measurements EN. Results have shown that the alloys exhibited an active–passive behavior regardless of the heat treatment. For alloys without heat treatment, the most corrosion resistant was the Ni3Al base alloy, but when they were heat treated, the most corrosion resistant was the alloy containing 3%Li. EIS results showed that for short immersion tests, the corrosion process was under diffusion control, but for longer exposure times, the presence of a protective scale was evident. All the alloys were highly susceptible to a localized type of corrosion according to EN measurements and supported by SEM micrographs. [Copyright &y& Elsevier]

Al-Cu-Mg-Ag-Zr alloys containing 0, 0.1, 0.3 and 0.5 mass%Sc were prepared by ingot metallurgy and thermomechanical treatment. The effect of Sc addition on the precipitation and microstructure of the alloys has been investigated by using mechanical testing, optical microscopy, scanning electron microscopy and transmission electron microscopy. It has been shown that trace Sc element refines the grains of the casting alloys and the average grain size decreases from 85 to 30 µm. Increasing Sc content from 0.1 to 0.3% accelerates the aging hardening process, increases the maximum hardness and the yield strength of the extruded alloys from room temperature to 300°C. The high strength of the alloys with Sc is attributed to the high density and high thermal stability of fine Ω precipitates, and nanosized Al3(Sc,Zr) and AlCu(Zr, Sc) particles. [ABSTRACT FROM AUTHOR]

Abstract: The effect of heat treatment temperature on the microstructure and mechanical properties of a Fe–4.0C–18.0Cr–1.0Mo–1.0Ti (wt.%) hypereutectic high chromium white cast iron was investigated. The response of the alloy to heat treatment and, therefore, the microstructures developed, differed significantly. With the increase of the heat treatment temperature, the precipitated secondary carbides changed from M3C to M7C3 and the retained austenite content increased. With the increase of the heat treatment temperature, the bulk hardness and matrix microhardness both increased and reached peak values of 64.6HRC and 850HV, respectively at the temperature of 1000°C. But they all decreased at the heat treatment temperature of 1050°C. The impact toughness of the alloy increased significantly compared with the conventional cast hypereutectic high chromium white iron (containing 4.0wt.% C and 17.0wt.% Cr) without titanium and inoculation and its value was in the range of 6.1–6.9J/cm2, but it did not change very much with the increase of heat treatment temperature. [Copyright &y& Elsevier]

The effect of heat treatment on the physicochemical and technological properties of aluminum-based powder materials containing rare-earth elements is investigated. Powder composites are produced by mechanical alloying in ball mills. Recommendations for molding and heat treatment conditions are given. [ABSTRACT FROM AUTHOR]

Abstract: The Ni–P alloy coatings with phosphorous content from 8.7 to 13.9wt.% were prepared in this study by pulse current electroforming. The effects of operating conditions of electroformed Ni–P coatings on the phosphorous contents and micro-hardness of the deposits were investigated. The heat treatment effects on the morphology and grain size was evaluated by X-ray diffraction. The effects of heat treatment on the hardness and wear resistance were also investigated. Our results show that the internal stress within the pc Ni–P deposited coating is much lower than that of dc Ni–P deposited coating and the phosphorus content profile is also more stable than that of dc Ni–P deposited coating. The grain size of as-plated Ni–P deposited coating is smaller than 1.5nm, but as the phosphorus content increased, both the grain size and microhardness decrease. After heat-treated at 400°C, the hard Ni3P phase precipitates and the grain size become gross, however, the grain size is still smaller than 5nm. The hardness of heat-treated coating can be enhanced efficiently and is well above 1000HV. It leads to a lower wear rate for heat-treated coating. The wear resistance of heat-treated coating can be as high as 2.5 times that of as-plated coating. In addition, the wear resistance and hardness increases with the increasing of grain size for both as-plated and heat-treated coatings. It suggests that the strength and grain size of the Ni–P coating with high phosphorus content obeys the inverse Hall–Petch relationship. [Copyright &y& Elsevier]

Abstract: In the present study, the effects of re-solution treatment of AA2618 aluminum alloy has been investigated. Solution heat treatments of 520–640 °C for 14–24 h were applied followed by artificial aging. Characterization studies that were carried out by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy techniques showed that recrystallisation was not observed by solution treatment at 530 °C whereas it did occur as the solution treatment and the duration time were increased above 530 °C. Increasing the solution treatment temperature further coarsened both the grains and the precipitates, resulting in significant reduction in hardness. Al9FeNi-type intermetallics are not completely dissolved by these solution treatments. [Copyright &y& Elsevier]

The influence of a dc electric field E = 5 kV/cm applied during the solution heat treatment (SHT) of the Al–Mg–Si alloy AA6022 at 475–552 °C on the subsequent natural aging kinetics was determined employing resistivity. It was found that the increase in the as-quenched resistivity which resulted from application of the field during SHT was retained throughout the natural aging process. An Avrami-type analysis of the natural aging kinetics gave n avg. = 0.3 and k avg. = 5 × 10−2 (min−1)0.3. These values are in qualitative accord with those determined for the Al–Mg–Si–Cu alloy AA6111. [ABSTRACT FROM AUTHOR]

The microstructural and mechanical characterization of heat treatable 6xxx (Al-Mg-Si-Cu based) wrought aluminum alloys was studied. The aim of this work was to produce a fine grained, high strength 6xxx series aluminum alloy by adjusting the processing conditions, namely deformation, solutionizing and aging. Their effects were investigated in terms of microstructure using SEM analysis and mechanical properties by tensile tests and hardness measurements. The initial characterizations showed that Mg2Si and (Fe,Mn,Cu)3SiAl12 were the primary particles observed in the α-Al matrix. Nearly 140HB hardness was obtained with solutionizing at 530 °C and aging at 175 °C for 8 h, which was the optimum treatment for obtaining peak hardness. When shaping (deformation) was concerned, 10% swaging before solutionizing yielded lower strength and hardness as compared to the 40% swaging due to lower strains finalizing partial recrystallization in the 10% swaged specimens. [ABSTRACT FROM AUTHOR]

Abstract: Titanium hydride was used for foaming the aluminium casting alloy AlSi6Cu4. In order to improve foaming characteristics the TiH2 powder was subjected to various heat treatments prior to processing to shift hydrogen release up into the melting range of the alloy. Untreated and pre-treated powders were characterised by oxygen analysis, thermal analysis in conjunction with mass spectrometry applying various temperature profiles, X-ray diffraction and transmission electron microscopy. In addition, foaming trials were carried out based on various TiH2 powders. It was found that oxidation of TiH2 particles is responsible for the observed shift in decomposition temperature since heating under argon did not produce this effect. The shift can be tailored by choosing suitable pre-treatment parameters. With an appropriate choice a beneficial effect on foam morphology was found. [Copyright &y& Elsevier]

The effect of different heat treatments (T5 and T6) on mechanical properties, fracture behavior and damage evolution of A356 Thixocast aluminum alloy have been examined in detail in the present work. Tensile tests of the material have been performed in the as cast and as treated conditions in order to observe the different fracture behavior in consequence of the heat treatments. Optical and scanning electron microscopy techniques have been used to characterize the microstructure and fracture surfaces of the specimens. Finally, the precipitation processes of the material have been analyzed by hardness and electrical conductivity measurements and EDS analysis has been used to characterize the different phases in the as-thixo and as-treated conditions. [ABSTRACT FROM AUTHOR]

Tempering treatments T4, T5 and T6 have been applied after thixoforming to investigate the effects of heat treatment on microstructure and mechanical properties of thixoformed wrought aluminium alloy 2014, a ‘modified’ 2014 and high strength casting aluminium alloy 201. The ‘modified’ 2014 was a simplified version of 2014 with composition (wt%) Cu 3.87, Mg 0.6 and Si 0.14. The results showed that standard solution time for conventional wrought alloy 2014 (1 h at 500°C) gave incomplete homogenisation of thixoformed material. Longer times (5 and 17 h) at 500°C are required for complete solutionisation of CuAl2. Low hardness values in the as-thixoformed 2014 were increased by subsequent heat treatment. After 18 h ageing at 160°C, the hardness of material solutionised for 5 and 17 h is higher than that for the standard 1 h. The tensile properties of the thixoformed 2014 were improved and close to those of forged 2014 using optimised post-forming heat treatment (solution treatment for 17 h at 500°C followed by water quenching and then ageing for 24 h at 160°C). Thixoformed alloy 201 in the standard T6 condition (2 h at 513°C followed by 17 h at 527°C and water quenching and then ageing 20 h at 153°C) showed a significant improvement over permanent mould casting. Good elongation to fracture (19.6%) was found for thixoformed ‘modified’ 2014 in the T6 condition. [ABSTRACT FROM AUTHOR]

This paper considers the process of change in the structure of aluminum films on silicon in metallizing integrated microcircuits under the conditions of both prolonged and fast thermal treatment. We propose an analytical model of the formation and recrystallization of condensed aluminum films. It is based on the application of the Monte Carlo method and describes the change in the size and angles at triple points depending on the temperature and time of thermal treatment. [ABSTRACT FROM AUTHOR]

The article discusses the effect post-weld heat treatment (PWHT) on the mechanical properties of 2219-O aluminum alloy friction stir welded joints (FSWJ). The PWHT process includes solid solution at 535 degree Celsius for 32 minutes, quenching in water at 25 degree Celsius, and ageing at 165 degree Celsius for 18 hours. During the heat treatment, it was observed that the tensile properties of the heat-treated joints increase with increasing welding speed. It shows that the PWHT process can significantly improved the tensile strength of the FSWJ of 2209-O aluminum alloy.