Quench Factor Research Articles

Modelling heat treatment of age hardenable cast aluminium alloys

Abstract The effects of solutionising time, cooling rate in quenching and aging time on the microstructure and mechanical properties of age hardenable cast Al alloy A356 have been experimentally investigated using the Jominy end quench method. The results indicate that the solutionising time for permanent mould cast alloys can be reduced from 10 to <4 h depending on the as cast microstructure and secondary dendrite arm spacing. The aging time increases the hardness of cast Al alloy A356 in the range of 2 up to 10 h. The experimental quenching rates and Meyer hardness along a Jominy end quench bar were used as inputs for quench factor modelling. The kinetic parameters were estimated using multiple linear regression analysis. A time–temperature property curve for a cast Al alloy A356 has been generated using the kinetic parameters and this result was experimentally verified. The predicted property data agreed well with that experimentally measured. Quench factor analysis has been proved to be applicable to ...

Heat treatment-modulated coupling effect of multi-scale second-phase particles on the ductile fracture of aged aluminum alloys

Experiments and multi-scale modeling were carried out in order to study the heat treatment-modulated coupling effect of multi-scale second-phase particles on the ductile fracture of two typical kinds of heat-treatable aluminum alloys, i.e. an Al–Cu–Mg alloy and an Al–Mg–Si alloy. It was revealed experimentally and theoretically that an appropriate combination of the multi-scale second-phase particles, which could be achieved by appropriate cooperation of the heat treatment steps, i.e. the solution, quenching and aging treatments, is necessary and sufficient for obtaining an excellent fracture toughness for the heat-treatable aluminum alloys. The experimental phenomenon, that the alloys containing more detrimental constituents but aged at a somewhat higher temperature exhibit ductility and fracture toughness superior to those of the alloys containing less detrimental constituents but aged at lower temperatures, could be reasonably explained by the cooperative effect of the heat treatment steps. Contours of the fracture toughness with respect to the technological parameters of the heat treatment, e.g. the aging temperature and quench factor, were developed to show the cooperative effect of the heat treatment steps on the fracture toughness of the aged aluminum alloys quantitatively. The good agreement between the calculations and the experimental results indicated that the present modeling is applicable for describing the heat treatment-modulated coupling effect of the multi-scale second-phase particles in aged aluminum alloys.

Measurement of nuclear recoil quenching factors in CaWO4

The CRESST experiment, aiming at the direct detection of WIMPs via nuclear recoils, is currently using scintillating CaWO4 crystals. The WIMP–nucleus cross section for elastic scattering as well as the scintillation efficiency differ considerably for recoils from Ca, W and O in these crystals. Therefore a discriminating detector calibration is essential in order to improve WIMP parameter claims. At the tandem accelerator of the Maier-Leibnitz-Laboratory (MLL) in Garching, Germany, a neutron scattering facility is operated for the determination of the individual quenching factors (QF) in the bulk of a CaWO4 crystal to better understand the detector response to neutron background and a possible WIMP signal. First measurements at room temperature reveal QF(O)=7.8±0.3% (recoil energy 1.0–2.2MeV), QF(Ca)=6.3±1.6% (recoil energy 0.4–1MeV), QF(W)<3.0% (2σ, recoil energy 0.1MeV).

Measurement of the scintillation light quenching at room temperature of sodium recoils in NaI(Tl) and hydrogen recoils in NE 213 by the scattering of neutrons

At the newly installed neutron scattering facility for the calibration of Dark Matter (DM) detectors we have measured quenching factors (QFs) at room temperature in NE 213 and NaI(Tl). For proton energies E p between 1 and 3.5 MeV we found the electron-equivalent energy E ee to obey the relation E ee = ( 0.23 ± 0.03 ) E p + ( 0.02 ± 0.01 ) E p 2 . The QF of the light output from Na recoils in NaI(Tl) at 850 keV was measured to be Q = 0.21 ± 0.04 .

Quench factor analysis of aluminium alloys using the Jominy end quench technique

Determination of the time–temperature property C curve for aluminium alloys usually involves a large number of quenches and isothermal holds to calibrate a set of constants that describes the shape of the C curve for a particular property. The authors have used the Jominy end quench test to minimise the amount of work required for this type of analysis. By matching the Vickers hardness at regular intervals along the length of the Jominy test specimen with cooling curves generated using finite element analysis (FEA), the constants of the C curve equation were determined using a single Jominy test specimen. It was possible to successfully predict the hardness down to 65% of the maximum achievable hardness with a maximum error of only 2·4%.

The application of advances in quench factor analysis property prediction to the heat treatment of 7010 aluminium alloy

7010 is an Al–Zn–Mg–Cu forging and plate alloy, primarily used in the aerospace industry for the production of key structural components. These alloys develop their strength through the development of a precipitation-hardened microstructure produced by ageing of a quenched super-saturated solid solution.For over 30 years Evancho and Staley developed quench factor analysis model has been applied successfully to the prediction of post-quenched physical properties, in aged aluminium alloys. In recent years improvements have been made to the initial model incorporating the effect of remaining solute on nucleation rate as a function of temperature. This extends the usefulness of the quench factor approach to beyond the 15% loss in properties, allowing the prediction of properties in both fast-quenched and slow-cooled conditions such as in annealing. Tensile time–temperature–property (TTP) or ‘C’ curves produced by an interrupted quench technique are presented for 7010-T76 including quench factor analysis and subsequent modifications based on an improved non-isokinetic model.

Residual stress reduction in 7175-T73, 6061-T6 and 2017A-T4 aluminium alloys using quench factor analysis

The quenching of aluminium alloys by immersion or spraying using cold water produces large thermal gradients in thick components such as forgings and plate. Whilst the rapid cooling ensures good mechanical properties the thermal gradients can be large enough to produce high levels of residual stress. Reducing the cooling rates during the quench can reduce the magnitude of the residual stresses, however it can also be detrimental to the mechanical properties, particularly for quench sensitive alloys. By generating time temperature property C-curves for each alloy and using quench factor analysis, it is possible to slowly cool the alloy from the solution heat treatment temperature to an intermediate temperature, above the critical temperature region of the C-curve, and then quench to room temperature. The result of this is a reduction in the residual stresses generated during the quench due to a reduced thermal gradient combined with a negligible effect on the mechanical properties of the alloys. The C-curves for the Vickers hardness have been generated for each alloy and temper and are presented. The residual stresses have been quantified for this alternative quenching route for each alloy and the Vickers hardness results are presented.

Flashback Limits for Combustion Induced Vortex Breakdown in a Swirl Burner

Flame flashback from the combustion chamber into the mixing zone limits the reliability of swirl stabilized lean premixed combustion in gas turbines. In a former study, the combustion induced vortex breakdown (CIVB) has been identified as a prevailing flashback mechanism of swirl burners. The present study has been performed to determine the flashback limits of a swirl burner with cylindrical premixing tube without centerbody at atmospheric conditions. The flashback limits, herein defined as the upstream flame propagation through the entire mixing tube, have been detected by a special optical flame sensor with a high temporal resolution. In order to study the effect of the relevant parameters on the flashback limits, the burning velocity of the fuel has been varied using four different natural gas-hydrogen-mixtures with a volume fraction of up to 60% hydrogen. A simple approach for the calculation of the laminar flame speeds of these mixtures is proposed which is used in the next step to correlate the experimental results. In the study, the preheat temperature of the fuel mixture was varied from 100°C to 450°C in order to investigate influence of the burning velocity as well as the density ratio over the flame front. Moreover, the mass flow rate has been modified in a wide range as an additional parameter of technical importance. It was found that the quenching of the chemical reaction is the governing factor for the flashback limit. A Peclet number model was successfully applied to correlate the flashback limits as a function of the mixing tube diameter, the flow rate and the laminar burning velocity. Using this model, a quench factor can be determined for the burner, which is a criterion for the flashback resistance of the swirler and which allows to calculate the flashback limit for all operating conditions on the basis of a limited number of flashback tests.

Improvements in quench factor modelling

In this contribution, the validity of a number of key quench factor analysis (QFA) assumptions is discussed. It is shown that the incorporation of a square root dependency of yield strength on precipitate volume fraction provides a sounder physical basis for quench factor modelling. Peak-aged strength/hardness prediction accuracies are not affected, but C-curve positions are. It is also demonstrated that transformation kinetics are described more correctly by a modified Starink–Zahra equation than by a Johnson–Mehl–Avrami–Kolmogorov type equation, yielding better prediction accuracies when a physically realistic Avrami exponent of 1.5 or greater is used. Finally, a regular solution model is introduced to quantify the influence of the solute solubility temperature-dependency on the minimum strength. These improvements are all implemented within the framework of classical QFA.

Greenhouse gas scenario in Indian continent

The ever-increasing importance of energy efficiency has given rise to numerous areas of concern for operators and developers of combustion plants; as the need to utilise fuel gases of increasingly poor quality and variability is essential for sustainability, while emission standards continuing to become more stringent. Swirl combustors are ubiquitous in industry owing to their great stability range which occurs due to the formation of a CRZ, which through the recycling of heat and active chemical species to the root of the flame enhances stability over a wide range of operating conditions.Alternative fuels containing hydrogen offer the possibility of reduced greenhouse gas emissions; however flashback is of special concern with hydrogen enriched fuels, owing to the very high flame speed of hydrogen. Many by-products of process and waste industries can include a high proportion of hydrogen, for example Coke Oven Gas. Alternatively, many by-product process gases can contain a high proportion of non-combustible species such as nitrogen and carbon dioxide which can substantially reduce their flame speed and as a consequence increase the possibility of the flame extinguishing through blow-off.This paper examines the blow-off and flashback potential of common steelworks process gases (including one which contains hydrogen) in a compact, premixed swirl burner in swirl number regimes representative of those found in practical systems. Methane is used as a base fuel for comparison. All results are obtained at atmospheric pressure without air preheat.The Peclet number modelling approach incorporating a flame quenching parameter was applied to the results obtained for each of the fuel gases. Using this model, the quench factor value was seen to be dependent on burner configuration as well as fuel composition.It was found that the stable burner operating conditions significantly change from fuel to fuel; with the operating points at which flashback occurs with Coke Oven Gas producing blow-off with weaker process gases such as Blast Furnace Gas and Basic Oxygen Steelmaking gas.

The influence of stopping power on the ionisation quench factor

Stopping power values for high energies have been computed applying the first Born approximation and the Bethe formula. However, this approximation tends to overestimate these cross sections at low energies, reaching discrepancies on the order of 50% at energies below 1 keV for most of the molecular targets of interest. In this paper we propose a method to obtain accurate low energy stopping powers of electrons by combining total cross section measurements with a theoretical treatment of the elastic process. We determine the optimum value of the kB parameter of ionisation quenching for the stopping power obtained in this paper.

Recent Improvement in High Strength Thick AA7050-Plate

The aircraft industry is constantly striving for improved materials which enables higher performance at reduced cost. The development of high speed milling machines and improvements in thick plate properties regarding distortion during machining have led to the conclusion that large machined structures can replace forged components and significantly reduce the cost by reducing the number of components and joints. For this reason, Hoogovens Aluminium Rolled Products together with Hoogovens Research and Development, has continued to improve the property balance required for AA7xxx high strength thick plates in aerospace applications. This paper will focus on investigations performed to optimise the process for high strength thick plates. This work contains a careful analysis of the process steps including the measurement of quench rate within thick plates, quench factor analysis, simulation of the effect of changes in quench practice on final properties and modelling work of residual stress to gain the best property balance required for thick plates in aerospace applications. Finally, the improved mechanical properties and the low level of distortion during machining for high strength thick plates will be discussed.

Quench modelling of Al-7Si-Mg casting alloys

Quench factor analysis was applied to A356 and A357 aluminium casting alloys in order to model time-temperature-yield strength curves, to predict T6 yield strengths as a function of continuous cooling quench rate and to examine quench sensitivity. The predicted T6 yield strengths for given quench curves were typically within ± 10 MPa of experimentally measured yield strengths. It was found that A356 is more quench sensitive than A357 at high quench rates, whereas A357 is more sensitive at low quench rates. This is explained in terms of silicon clustering, which alters the matrix Mg/Si ratio and subsequent precipitation events. These observations were confirmed by differential scanning calorimetry.

Analysis of linear and cyclic oligomers in polyamide-6 without sample preparation by liquid chromatography using the sandwich injection method: II. Methods of detection and quantification and overall long-term performance

By separating the first six linear and cyclic oligomers of polyamide-6 on a reversed-phase high-performance liquid chromatographic system after sandwich injection, quantitative determination of these oligomers becomes feasible. Low-wavelength UV detection of the different oligomers and selective post-column reaction detection of the linear oligomers with o-phthalic dicarboxaldehyde (OPA) and 3-mercaptopropionic acid (3-MPA) are discussed. A general methodology for quantification of oligomers in polymers was developed. It is demonstrated that the empirically determined group-equivalent absorption coefficients and quench factors are a convenient way of quantifying linear and cyclic oligomers of nylon-6. The overall long-term performance of the method was studied by monitoring a reference sample and the calibration factors of the linear and cyclic oligomers.

The ionization quench factor in liquid-scintillation counting standardizations

We present a new detailed analysis of the ionization quench function Q( E) used in calculating the counting efficiency in liquid-scintillation counting (LSC), which shows that Q(0)=1, and permits one to derive Q( E) as a function of the electron energy and the parameter kB. The coefficients are tabulated by applying a new empirical formula of Q( E) for kB values in the range between 0.001 and 0.20 gMeV −1 cm −2. We demonstrate the convenience of applying 3H and 54Mn for β-ray and electron capture standardizations, respectively.

Cooling Curve and Quench Factor Characterization of 2024 and 7075 Aluminum Bar Stock Quenched in Type 1 Polymer Quenchants

Cooling Curve and Quench Factor Characterization of 2024 and 7075 Aluminum Bar Stock Quenched in Type 1 Polymer Quenchants

Validation of a systematic approach to modeling spray quenching of aluminum alloy extrusions, composites, and continuous castings

Optimal cooling of aluminum alloys following the high- temperature extrusion process suppresses precipitation of intermetallic compounds and results in a part capable of possessing maximum strength and hardness after the subsequent age- hardening process. Rapid quenching suppresses precipitation but can lead to large spatial temperature gradients in complex- shaped parts, causing distortion, cracking, high residual stress, and/or nonuniform mechanical properties. Conversely, slow cooling significantly reduces or eliminates these undesirable conditions but allows considerable precipitation, resulting in low strength, soft spots, and/or low corrosion resistance. This study presents a systematic method of locating and operating multiple spray nozzles for any shaped extrusion such that uniform, rapid cooling and superior mechanical and metallurgical properties are achieved. A spray nozzle data base was compiled by measuring the distribution of spray hydrodynamic parameters (volumetric spray flux, mean drop diameter, and mean drop velocity) throughout the spray field of various industrial nozzles. Spray heat transfer correlations, which link the local spray hydrodynamic parameters to the heat transfer rate in each of the boiling regimes experienced by the surface, defined the spatially nonuniform boundary conditions in a numerical model of the quenching process that also accounted for interference between adjacent spray fields. New correlations, offering increased accuracy and less computational time, were formulated for the high- temperature boiling regimes which have a critical influence on final mechanical properties. The quench factor technique related predicted thermal history to metallurgical transformations occurring within the extrusion to predict hardness distribution. The validity of this unique approach was demonstrated by comparing model predictions to the temperature response (and hardness after artificial aging) of an L- shaped Al 2024- T6 extrusion to quenches with multiple, overlapping water sprays. The validation study reported herein concludes by exploring the possibility of applying quenching technology to improving the properties of extruded metal- matrix composites such as SiCp/Al 6061 and cast alloys.

Predicting the Impact of Quenching on Mechanical Properties of Complex-Shaped Aluminum Alloy Parts

The mechanical properties of age-hardenable aluminum alloy extrusions are critically dependent on the rate at which the part is cooled (quenched) after the forming operation. The present study continues the development of an intelligent spray quenching system, which selects the optimal nozzle configuration based on part geometry and composition such that the magnitude and uniformity of hardness (or yield strength) is maximized while residual stresses are minimized. The quenching of a complex-shaped part with multiple, overlapping sprays was successfully modeled using spray heat transfer correlations as boundary conditions within a finite element program. The hardness distribution of the heat-treated part was accurately predicted using the quench factor technique; that is, the metallurgical transformations that occur within the part were linked to the cooling history predicted by the finite element program. This study represents the first successful attempt at systematically predicting the mechanical properties of a quenched metallic part from knowledge of only the spray boundary conditions.

Validation of the quench factor technique in predicting hardness in heat treatable aluminum alloys

This paper explores the relationship between the heat transfer mechanisms and metallurgical transformations associated with spray quenching in the heat treating of aluminum alloys. A method known as the quench factor technique is presented as a means for predicting the hardness and strength of aluminum alloys following a procedure of solution heat treatment with spray quenching and artificial age-hardening. It is shown that the only input parameter for predicting hardness of a particular alloy is its temperature-time history during quenching. Temperature-time quench data measured both in small specimens and a relatively large L-shaped specimen are combined with metallurgical transformation data for aluminum alloy 2024-T6 to predict Rockwell B hardness. The predicted hardness compares well with the values measured for both types of specimens. These results both demonstrate the validity of the quench factor technique and emphasize the need for tools which would facilitate accurate prediction of the temperature-time history during spray quenching. Such tools could ultimately enable the aluminum industry to produce parts with both large and uniform hardness and strength by careful manipulation of the sprays.

Effects of spray configuration on the uniformity of cooling rate and hardness in the quenching of aluminum parts with nonuniform shapes

The present study constitutes a step toward the understanding, and eventual optimization, of the spray quenching process for aluminum extrusions. A spray quenching test bed was constructed to simulate an industrial spray quench. This experimental facility allowed for the testing of irregular shapes using up to eight water sprays. Quenching experiments were conducted using flat water sprays in two different configurations with an L-shape testpiece constructed from commercially pure aluminum Al 1100-O. Section thickness and spray configuration were found to have a significant effect on the cooling rate and cooling uniformity. The commercially pure aluminum Al 1100-O L-shape and a similar L-shape constructed from aluminum alloy 2024-T6 were simulated with a two-dimensional finite-element code and spray correlations available from previous studies. Using the quench factor technique, the numerical simulation enabled the assessment of merits of different spray configurations with respect to the magnitude and uniformity of hardness of the 2024-T6 L-shape.