Quench Factor Analysis Research Articles

The Influence of Quenching and Aging on Fracture Toughness of the Al-Zn-Mg-Cu Alloy 7449

Abstract This investigation characterises the fracture toughness of the very high strength Aluminium alloy 7449. This Al-Zn-Mg-Cu alloy is heat treatable and relies on rapid quenching from the solution heat treatment temperature to promote subsequent artificial aging. While the influence of quench paths on strength is well understood and can be predicted using techniques like quench factor analysis, the influence of quench rate on fracture toughness is more challenging. The rate of quenching can influence the fracture toughness through complex precipitation reactions occurring during cooling. The precipitate locations dictate the magnitude of the detrimental effect on the fracture toughness. In this investigation, the fracture toughness of 7449 in two product forms was measured using compact tension specimens cut from forged blocks and rolled plate. These plane strain (KIC) results were also augmented with Charpy impact tests. Various quench conditions were investigated, including water at three different temperatures and poly oxyethylene glycol (PAG) in two concentrations. The influence of standard and novel aging procedures including retrogression and reaging was also determined. The combinations of strength and toughness have been related to the prevailing microstructural condition. Fracture toughness magnitudes were found to vary most significantly with rapidity of cooling from the solution treatment temperature, with the subsequent aging treatments having a much smaller effect.

On the quench sensitivity of 7010 aluminum alloy forgings in the overaged condition

Abstract The quench sensitivity of an overaged 7010 alloy forging was characterized by tensile and Vickers hardness tests, as well as scanning electron microscopy. Longitudinal tensile specimens, excised from a rectilinear open die forging were cooled from the solution treatment temperature following thirty-two different cooling paths including interrupted and delayed quenches. SEM analysis of the microstructure showed that quench precipitates were (i) Al 2 CuMg (S) which nucleated heterogeneously on grain boundaries and (ii) Mg(Zn,Cu,Al) 2 (η) on grain boundaries, dispersoid bands, subgrain boundaries as well as in the aluminum matrix. The quench sensitivity of the alloy׳s yield strength and Vickers hardness was modeled simultaneously by quadruple-C curves, using an improved methodology for Quench Factor Analysis. The four C-curves used in the model represented loss of solute by (i) precipitation of S on grain boundaries, and precipitation of η (ii) on grain boundaries and dispersoid bands, (iii) on subgrain boundaries and (iv) in the matrix. The model yielded coefficient of determination ( R 2 ) values of 0.967 and 0.974 for yield strength and Vickers hardness, respectively. The model and the implications of the results are discussed in this paper.

Isothermal Time-Temperature-Precipitation Diagram for an Aluminum Alloy 6005A by In Situ DSC Experiments.

Time-temperature-precipitation (TTP) diagrams deliver important material data, such as temperature and time ranges critical for precipitation during the quenching step of the age hardening procedure. Although the quenching step is continuous, isothermal TTP diagrams are often applied. Together with a so-called Quench Factor Analysis, they can be used to describe very different cooling paths. Typically, these diagrams are constructed based on mechanical properties or microstructures after an interrupted quenching, i.e., ex situ analyses. In recent years, an in situ calorimetric method to record continuous cooling precipitation diagrams of aluminum alloys has been developed to the application level by our group. This method has now been transferred to isothermal experiments, in which the whole heat treatment cycle was performed in a differential scanning calorimeter. The Al-Mg-Si-wrought alloy 6005A was investigated. Solution annealing at 540 °C and overcritical quenching to several temperatures between 450 °C and 250 °C were followed by isothermal soaking. Based on the heat flow curves during isothermal soaking, TTP diagrams were determined. An appropriate evaluation method has been developed. It was found that three different precipitation reactions in characteristic temperature intervals exist. Some of the low temperature reactions are not accessible in continuous cooling experiments and require isothermal studies.

Application of QFA coupled with CFD analysis to predict the hardness of T6 heat treated Al6061 cylinder

QFA (quench factor analysis) method is widely used to predict the mechanical properties such as hardness and strength according to temperature of quenched material that has to be determined by experimental heat treatment. But, QFA coupled with CFD (computational fluid dynamics) analysis of this study can predict the mechanical properties without the experiment of heat treatment except the experiment to determine the material constants of QFA. First of all, Jominy test and FPS (flexible polyhedron search) are performed to determine the material constants of QFA. The CFD analysis is applied to predict the cooling temperature of Al6061 cylinder cooled by water of 25°C during quenching of solid solution heat treatment. Hardnesses of T6 heat treated Al6061 cylinder is predicted by the QFA coupled with CFD analysis without experiment of heat treatment and then the predicted hardnesses are compared with experimentally measured hardnesses according to positions of cylinder. The predicted hardnesses of cylinder are in good agreement with the measured ones within a maximum error of 8.45%.

Quench sensitivity of 6351 aluminum alloy

The quench sensitivity of 6351 alloy was determined by the time–temperature-transformation (TTT) curves and time– temperature-property (TTP) curves by an interrupted quench technique with measurement of as-aged hardness and as-quenched electro-conductivity. The microstructure transformation during isothermal treatment was studied by the transmission electron microscopy (TEM) and Avrami equation. The results showed that the electro-conductivity of the 6351 alloy increased and the hardness decreased with prolonging the holding time at a certain isothermal temperature. The TEM observation indicated that the supersaturated solid solution decomposed and needles β″ precipitated at the initial stage of isothermal holding. With the prolongation of holding time at the nose temperature, rod β′ and plate β phases formed. The isothermal transformation rate at 360 °C was the fastest, and became slow at 280 °C and reached the slowest at 440 °C. The nose temperatures of the TTT and TTP curves were about 360 °C and the high quench sensitive temperature range was 230–430 °C. The quench factor analysis indicated that the cooling rate should be more than 15 °C/s in the quench sensitive areas in order to get optimal mechanical properties.

Improvement of Quench Factor Analysis in Phase and Hardness Prediction of a Quenched Steel

The accurate prediction of alloys’ properties introduced by heat treatment has been considered by many researchers. The advantages of such predictions are reduction of test trails and materials’ consumption as well as time and energy saving. One of the most important methods to predict hardness in quenched steel parts is Quench Factor Analysis (QFA). Classical QFA is based on the Johnson–Mehl–Avrami-Kolmogorov (JMAK) equation. In this study, a modified form of the QFA based on the work by Rometsch et al. is compared with the classical QFA, and they are applied to prediction of hardness of steels. For this purpose, samples of CK60 steel were utilized as raw material. They were austenitized at 1103 K (830 °C). After quenching in different environments, they were cut and their hardness was determined. In addition, the hardness values of the samples were fitted using the classical and modified equations for the quench factor analysis and the results were compared. Results showed a significant improvement in fitted values of the hardness and proved the higher efficiency of the new method.

Influence of quenching and aging on residual stress in Al–Zn–Mg–Cu alloy 7449

The present investigation aims to quantify the size and distribution of residual stresses remaining in rectilinear aluminium forged alloy blocks after they had been partially and fully heat treated. Various quench conditions were used, including water at different temperatures and polyoxyethylene glycol in two concentrations. The influence of standard and novel aging procedures, including retrogression and reaging, has been determined. Residual stresses were characterised using X-ray and neutron diffraction. Residual stress magnitudes were found to vary significantly with rapidity of cooling from the solution treatment temperature, with the subsequent aging treatments having a much smaller effect. The influence of heat treatments on the mechanical properties of the alloy was predicted by means of quench factor analysis and measured using indentation hardness and tensile testing. Quench factor analysis is also used to predict the change in lattice parameter arising from different quench paths in the strain free reference samples d0.

Investigation of quench sensitivity and transformation kinetics during isothermal treatment in 6082 aluminum alloy

The quench sensitivity of 6082 aluminum alloy was investigated by time–temperature–property (TTP) curves. The sensitive temperature of quenching ranges from 250 °C to 440 °C in 6082 Al-alloy, and the nose temperature is about 360 °C. During isothermal treatment process, the Mg 2Si particles precipitate from the supersaturated solid solution, and the precipitation rate is the highest at the nose temperature. A number of rod-shaped β′ and β particles precipitate in the early stage of isothermal treatment at 360 °C. Prolonging the holding time leads to more and coarser β particles in the matrix. Both the precipitation of β′ and β particles results in loss of solute and decreasing of the subsequent age hardening effect. Also, the important coefficients k 2– k 5 and critical cooling rate for 6082 Al-alloy are identified, and the properties after different rates of cooling were predicted using quench factor analysis.

Heat transfer coefficients during quenching of steels

Heat transfer coefficients for quenching in water have been measured as a function of temperature using steel probes for a variety of iron alloys. The coefficients were derived from measured cooling curves combined with calculated heat-capacities. The resulting data were then used to calculate cooling curves using the finite volume method for a large steel sample and these curves have been demonstrated to be consistent with measured values for the large sample. Furthermore, by combining the estimated cooling curves with time-temperature-transformation (TTT) diagrams it has been possible to predict the variation of hardness as a function of distance via the quench factor analysis. The work should prove useful in the heat treatment of the steels studied, some of which are in the development stage.

Modeling Quench Sensitivity of Aluminum Alloys for Multiple Tempers and Properties: Application to AA2024

Quench factor analysis (QFA) was developed to predict the change in certain properties, such as yield strength, hardness, electrical conductivity, etc., with how the material cools from solution treatment temperature during quenching. This method necessitates that a set of coefficients be developed by laboratory testing for a particular alloy in a given temper. In the original QFA, these coefficients have been developed independently for each physical property of each temper that might be produced from the same alloy. However, properties used commonly to assess quench sensitivity, e.g., electrical resistivity, hardness tests, tensile tests in different directions, etc., all respond to the same physical change during quench: loss of solute caused by the precipitation of quench precipitates. The QFA method has been modified to handle multiple properties and multiple tempers. The new method allows multiple C-curves for multiple phases and/or nucleation mechanisms for quench precipitates. The advantages of this method include better statistical resolution when fitting multiple data concurrently and possible substitution of a cheaper test for the property and temper of interest. The use of this approach is demonstrated on data sets for aluminum alloy 2024 within this study.

Quench sensitivity of 2219-T87 aluminum alloy plate

The quench sensitivity of 6.4mm thick 2219-T87 plate was investigated by using the improved quench factor analysis method and the data of Swartzendruber et al. (NBSIR 80-2069, National Bureau of Standards, 1980). This study was exceptional for the breadth and quality of the investigations. The close integration of the quench factor analysis (QFA) with such a broad and deep independent study of commercial material, was significant in establishing awareness and credibility of QFA. The report by Swartzendruber et al., by the very breadth and depth, exposed some limitations of the QFA. The report did not include emphasizing these limitations nor attempting a remedy. The intention of the present paper is to demonstrate how the QFA can be extended to deal with the limitations implicitly exposed by Swartzendruber et al. The quench sensitivity of the alloy's yield strength was modeled by three C-curves which represented loss of solute by precipitation of (i) θ phase on grain boundaries, (ii) θ phase in the matrix, and (iii) θ′ phase on matrix dislocations, which is consistent with previous findings reported in the literature. The model and the implications of the results are discussed in the paper.

Investigation of quench sensitivity of high strength Al–Zn–Mg–Cu alloys by time–temperature-properties diagrams

The quench sensitivity of some typical high strength Al–Zn–Mg–Cu alloys, including 7075, 7175, 7050, 7010, 7055, 7085 and 1933, was investigated by time–temperature-properties (TTP) diagrams which were from the present paper and literature. The drop in the mechanical properties due to decreased quenching rate was predicted by quench factor analysis method. The nose temperature of TTP diagrams was the highest for 7055 alloy and the lowest for 7085 alloy. The critical time at the nose temperature was the shortest for 7055 alloy and the longest for 1933 alloy. Decreased quenching rate to 10 k/s led to drop in the properties less than 2% for 7085 and 1933 alloys, but more than 20% for 7075, 7175 and 7055 alloy. Thus, 7075, 7175 and 7055 alloys were the most quench sensitive alloys, while 7085 and 1933 alloys were the least quench sensitive ones. The differences in the quench sensitivity of these alloys were explained mainly based on its chemical compositions.

Evolution of Quench Factor Analysis: A Review

Abstract One of the steps of the heat treatment process of age hardenable aluminum alloys is the quenching process in which the alloy is cooled from the solutionizing temperature. The objective is to quench sufficiently fast to avoid undesirable concentration of alloying elements in the defect and grain boundary structure, while at the same time not quenching faster than necessary to minimize residual stresses, which may lead to excessive distortion or cracking. Various studies have been conducted to predict the relative quench rate sensitivity to yield different properties for age-hardenable alloys. Of these different predictive methods, the one that showed the more realistic results is quench factor analysis since it involves a correlation of the cooling curve (time-temperature curve) of the cooling process throughout the quenching cycle for the desired cross-section size of interest with a C-curve (time-temperature-property curve) for the specific alloy of interest. The quench factor analysis numerical procedure has evolved since its original introduction. A review of the basic assumptions of the classical quench factor analysis model will be provided here which will include discussion of the various improvements to the classical model that have been proposed over the intervening years since its introduction.

Water and Polymer Quenching of Aluminum Alloys: A Review of the Effect of Surface Condition, Water Temperature, and Polymer Quenchant Concentration on the Yield Strength of 7075-T6 Aluminum Plate

Abstract Cold water is perhaps the most common quenchant used for heat treatable aluminum alloys. In many situations, excessive distortion and cracking problems require the use of a less severe quenchant such as hot water or a Type I aqueous polymer quenchant. However, when these alternative quenching media are used, the distortion improvement achieved is typically accompanied by a corresponding loss of strength. This paper will provide an overview of cold versus hot water quenching and the potential use of Type I polymer quenchants. The potential use of quench factor analysis to aid in quenchant media selection and corresponding property prediction is reviewed and applications are demonstrated. The often dramatic impact of the surface condition of aluminum on quenching performance and properties achieved will also be included in this review.

Prediction of hardness at different points of Jominy specimen using quench factor analysis method

Abstract Jominy end quench test is a standard test used to characterize hardenability of steels. There are some theories focused on correlation between cooling curves and hardness of the test specimen such as quench factor analysis (QFA). In this research it was tried to simulate the Jominy test of a steel (AISI 4130) with the method. By considering the phase transformation during quenching and material properties, cooling curves of different points were determined. Then, using time–temperature-properties (TTP) curve of 4130 steel, function constants of the curve ( C T ) were obtained. Finally, the QFA was derived using the simulated results and maximum and minimum hardness of the steel. The extracted results from QFA are hardness of different points of Jominy specimens. The data obtained from QFA were compared with the experimental results. The comparison showed a good agreement at the low specification but not at the high specification successfully.

A Methodology to Predict the Effects of Quench Rates on Mechanical Properties of Cast Aluminum Alloys

The mechanical properties of age-hardenable Al-Si-Mg alloys depend on the rate at which the alloys are cooled after the solutionizing heat treatment. Quench factor analysis, developed by Evancho and Staley, was able to quantify the effects of quenching rates on the as-aged properties of an aluminum alloy. This method has been previously used to successfully predict yield strength and hardness of wrought aluminum alloys. However, the quench factor data for aluminum castings is still rare in the literature. In this study, the time-temperature during cooling and hardness were used as the inputs for quench factor modeling. The experimental data were collected using the Jominy end quench method. Multiple linear regression analysis was performed on the experimental data to estimate the kinetic parameters during quenching. Time-temperature-property curves of cast aluminum alloy A356 were generated using the estimated kinetic parameters. Experimental verification was performed on a cast engine head. The predicted hardness agreed well with that experimentally measured. The methodology described in this article requires little experimental effort and can also be used to experimentally estimate the kinetic parameters during quenching for other aluminum alloys.

Prediction of Hardness of Aluminum Alloy 7055 by Quench Factor Analysis

The Vickers hardness time-temperature-properties (TTP) curve of aluminum alloy 7055 was evaluated by interrupted quench technique. The critical temperature range of TTP curve was determined from 210 °C to 420 °C with the nose temperature of 355 °C. The hardness decreased rapidly with isothermal duration in the critical temperature range. The hardness of aluminum alloy 7055 was predicted by quench factor analysis using the TTP curve and cooling curves. The predicted hardness agreed reasonably well with the measured results. The influence of time step and summation temperature range on the predicted results was studied. The cooling rate through the critical temperature range had dominant influence on the final hardness of the alloy.

Quench Sensitivity of an Al-7 Pct Si-0.6 Pct Mg Alloy: Characterization and Modeling

The quench sensitivity of a cast Al-7 wt pct Si-0.6 wt pct Mg alloy was characterized by tensile tests and scanning electron microscopy. Specimens were cooled from the solution treatment temperature following 58 different cooling paths including interrupted and delayed quenches. Analysis of the microstructure showed that quench precipitates were Mg2Si (β), which nucleated heterogeneously on Si eutectic particles as well as in the aluminum matrix, presumably on dislocations. The quench sensitivity of the alloy’s yield strength was modeled by multiple C-curves, using an improved methodology for quench factor analysis. The three C-curves used in the model represented loss of solute by (1) diffusion of Si to eutectic particles, (2) precipitation of β on Si eutectic particles, and (3) precipitation of β in the matrix. The model yielded a R 2 of 0.994 and a root-mean-square error (RMSE) of 7.4 MPa. The model and the implications of the results are discussed in the article.

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 ...

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%.