Time Temperature Property Research Articles

Quench sensitivity of A379 alloy under high-pressure die-casting and gravity-casting processes

Adding Cr to Al–Si–Mg alloys can eliminate the adverse effects of Fe, but can increase the quench sensitivity of the alloys. The influence of gravity-casting and high-pressure die-casting on the quench sensitivity of A379 (Al–7Si–0.5Mg–0.2Cr) alloys were studied using time–temperature–property curves. The nose temperatures of the gravity-casting- and high-pressure die-casting-fabricated specimens are near 350 °C and 355 °C, respectively. The temperature regions with high quench sensitivity characteristics of the former and latter occur from 310 °C to 390 °C and from 290 °C to 400 °C, respectively. The time–temperature–property curves of the high-pressure die-casting-fabricated samples are farther to the left than that of gravity-casting-fabricated samples, indicating that the high-pressure die-casting-fabricated specimens are more sensitive and are easier to generate precipitates than the gravity-casting-fabricated specimens during quenching because of the following reasons. For both specimens, the quench-induced precipitates (Mg xSi) nucleate on the Cr-containing dispersions in the grains, but the Cr-containing dispersions in the high-pressure die-casting-fabricated specimens are finer and more dispersible than in the gravity-casting-fabricated specimens. Meanwhile, the high-pressure die-casting-fabricated specimens exhibited finer grain sizes than the gravity-casting-fabricated specimens; thus, they can provide more grain boundary nucleation sites for forming the Mg xSi phase than the gravity-casting-fabricated specimens during isothermal treatment.

Quench Sensitivity of 7475 Aluminum Alloy Using End-Quenching Technique and TTP Diagrams

The quench sensitivity of 7475 aluminum alloy has been comprehensively investigated by hardness testing, electrical conductivity measurements, scanning electron microscopy, and transmission electron microscopy. Based on the end-quenching method and time–temperature–property (TTP) diagram, the key factors affecting the quenching of the studied alloy were identified and are discussed in comparison with other 7000 series alloys. The results indicate that 7475 alloy is relatively sensitive to cooling rate, with a critical temperature range between 300°C and 350°C. The nose temperature of the TTP curve is approximately 330°C, and the incubation period is 1.5 s. When the cooling rate is lower than 12.5°C/s, the density of Guinier–Preston zones and η′ precipitates decreases remarkably, and the width of the precipitate-free zone becomes wider. Simultaneously, coarse η phases precipitate at grain/subgrain boundaries and Al18Mg3Cr2 dispersoids. These quench-induced η phases consume numerous solute atoms and therefore suppress the formation of the strengthening precipitates, leading to a deterioration of the mechanical properties.

Investigation of the Quench Sensitivity of an AlSi10Mg Alloy in Permanent Mold and High-Pressure Vacuum Die Castings.

The quench sensitivities of an AlSi10Mg alloy in permanent mold (PM) and high-pressure vacuum die (HPVD) castings were investigated with time–temperature–transformation and time–temperature–property diagrams using an interrupted quench technique. The quench-sensitive temperature range of the HPVD casting sample is 275–450 °C, and its nose temperature is 375 °C. The quench-sensitive range of the PM casting sample is 255–430 °C, and the nose temperature is 350 °C. The mechanical strength versus the cooling rate in both casting samples were predicted via a quench factor analysis and verified experimentally. The critical cooling rate of the HPVD casting sample is 20 °C/s whereas it is 17 °C/s for the PM casting sample. With a shorter critical time, higher nose temperature, and higher critical cooling rate, the HPVD casting sample exhibits a higher quench sensitivity than the PM casting sample. The differences in the quench sensitivities of the AlSi10Mg alloy due to the different casting processes is explained via the different precipitation behavior. At the nose temperature, coarse β-Mg2Si precipitates mainly precipitate along the grain boundaries in the HPVD casting sample, whereas rod-like β-Mg2Si precipitates distribute in the aluminum matrix in the PM casting.

Quench sensitivity of Al–Cu–Mg alloy thick plate

The quench sensitivity of Al–Cu–Mg alloy was investigated at different thicknesses of the thick plate. The quenching process was simulated via finite element analysis (FEA); time–temperature–property (TTP) curves and time–temperature–transformation (TTT) curves were obtained through hardness test and differential scanning calorimetry (DSC) test; and the microstructural observation was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Experimental results exhibit that the quench cooling rate decreases dramatically from the surface to the center of the plate, and the inhomogeneous quenching causes the difference in microstructure. With the decrease in quench cooling rate, constituent particles are coarsening gradually; the quantity of T-phase (Al20Cu2Mn3) increases and the S-phase (Al2CuMg) decreases. According to the precipitation kinetics analysis, the decrease in S-phase is caused by the increase in precipitate activation energy. So that the center of the plate shows the highest quenching sensitivity, which is consistent with the analysis of time–temperature–property curves and time–temperature–transformation curves.

Hardness Prediction of Tailor Rolled Blank in Hot Press Forming Using Quench Factor Analysis

This paper aims to predict the hardness of hot formed part for tailor rolled blank (TRB) by the FE-simulation coupled with quenching factor analysis (QFA). Dilatometry test of boron steel is performed at various range of cooling rates from 0.2 to 100°C/s using the dilatometer with forced air cooling system. The dilatometry test provides a hardness data according to cooling curves which are used to determine the material constants (K1~K5) of QFA and the time‒temperature‒property (TTP) diagram of boron steel. Then, FE‒simulation of hot press forming is conducted to predict the cooling curves of hot formed TRB part with a thickness combination of thicker 1.6mm and thinner 1.2mm which is called as rear side member of automotive component. The cooling curves of FE-simulation are applied to predict the hardness of hot formed rear side member using the QFA. Also, experiment of hot press forming is performed to verify the predicted results and to examine the effect of cooling curves on the hardness.

Novel Method for Predicting Hardness Distribution of Hot-Stamped Part Using FE-Simulation Coupled with Quench Factor Analysis

In the hot stamping of boron-alloyed steel, the mechanical properties of hot-stamped parts have been predicted by many empirical models based on Kirkaldy’s equation. Although these models are skillfully developed, there is still a need to precisely and easily predict the mechanical properties in the hot stamping process. Therefore, this study aims to suggest a novel method for the accurate prediction of the hardness distribution of hot-stamped parts by the use of finite element (FE)-simulations coupled with quench factor analysis (QFA). First, dilatometry of boron steel was performed at various cooling rates from 0.5 to 70 K/s using a dilatometer with a forced-air cooling system. The dilatometry test provided hardness data according to the cooling rates, which were used to determine the material constants (K 1 to K 5) of the QFA and the time–temperature–property diagram of boron steel. Then, FE-simulation of hot stamping was conducted to obtain the cooling curves for blanks with thicknesses of 1.2 and 1.6 mm. The extracted results from the FE-simulation were used to predict the hardness distribution of the hot-stamped parts using QFA. Finally, a hot stamping experiment was performed to verify the predicted results and to examine the effect of the blank thickness on the cooling rates of a hot-stamped part. The predicted hardnesses for the parts were in good agreement with the measured values, within a maximum error of 4.96 pct.

Microstructure evolution and quench sensitivity of Cu–10Ni–3Al–0.8Si alloy during isothermal treatment

Abstract

Time–temperature–property curves for quench sensitivity of 6063 aluminum alloy

The quench sensitivity of 6063 alloy was investigated via constructing time–temperature–property (TTP) curves by interrupted quenching technique and transmission electron microscopy (TEM) analysis. The results show that the quench sensitivity of 6063 alloy is lower than that of 6061 or 6082 alloy, and the critical temperature ranges from 300 to 410 °C with the nose temperature of about 360 °C. From TEM analysis, heterogeneous precipitate β-Mg2Si is prior to nucleate on the (AlxFeySiz) dispersoids in the critical temperature range, and grows up most rapidly at the nose temperature of 360 °C. The heterogeneous precipitation leads to a low concentration of solute, which consequently reduces the amount of the strengthening phase β‘’ after aging. In the large-scale industrial production of 6063 alloy, the cooling rate during quenching should be enhanced as high as possible in the quenching sensitive temperature range (410–300 °C) to suppress the heterogeneous precipitation to get optimal mechanical properties, and it should be slowed down properly from the solution temperature to 410 °C and below 300 °C to reduce the residual stress.

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.

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.

TTP diagrams for aluminium alloy 1933

The Vickers hardness time–temperature–property (TTP) diagrams for aluminium alloy 1933 were constructed by an interrupted quenching technique. The nose temperature of TTP diagram for 99·5% maximum attainable hardness was about 310°C, at which the hardness decreased rapidly with increasing isothermal holding time. Comparison of TTP diagrams for 1933 and 7050 alloys indicated lower quench sensitivity for the former alloy. The reason was discussed mainly according to the difference in their chemical compositions.

TTP diagrams for 7055 aluminium alloy

The Vickers hardness and electrical conductivity time–temperature–property (TTP) diagrams for 7055 aluminium alloy were evaluated by an interrupted quench technique. The results show that the critical temperature range was approximately from 230 to 420°C, with the nose temperature of ∼355°C. Rapid decrease in hardness and increase in electrical conductivity were observed with isothermal holding within the critical temperature range.

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 ...

The Influence of Aluminium Alloy Quench Sensitivity on the Magnitude of Heat Treatment Induced Residual Stress

To produce useful strengthening, precipitation hardenable aluminium alloys rely on rapid quenching from the solution heat treatment temperature to suppress the formation of coarse equilibrium second phases. An unavoidable consequence of the rapid quenching of thick sections is the severe thermal gradients that quickly develop in the material. The attendant inhomogeneous plastic flow can then result in the establishment of residual stresses. The surface and through thickness residual stress magnitudes present in heat treated high strength aluminium alloy components are frequently reported to exceed the uniaxial yield stress of small specimens of the same alloy measured immediately after quenching. In thick section plate and forgings it is proposed that these high residual stress magnitudes are a consequence of hardening precipitation that occurs during quenching which allows for a greater elastic stress to be supported. To investigate this theory, thick sections of the quench sensitive alloy 7175 and the less quench sensitive alloy 7010 were heat treated in such a way as to allow the internal hardness to be measured immediately, after quenching. The rate of cooling was also monitored during quenching and these data were used in conjunction with time temperature property data to predict the degree of precipitation and subsequent loss of hardening potential in the fully heat treated condition. The magnitudes of the residual stresses induced during quenching were determined using standard x-ray diffraction techniques.

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.

Quench sensitivity and tensile property inhomogeneity in 7010 forgings

7xxx (Al–Zn–Mg–Cu) alloys develop their strength, through the controlled decomposition (ageing) of a supersaturated solid solution to produce a precipitation hardened microstructure. The supersaturated solid solution is normally produced by water quenching from the solution heat treatment temperature. The kinetics of phase transformations occurring during cooling from the solution heat treatment temperature are limited at small undercoolings by the small chemical free energy, and as the undercooling increases, by reduced rates of substitutional solid state diffusion. This gives rise to the characteristic C-shape of time–temperature-property (TTP) curves. The TTP curve for 7010 has been evaluated by a interrupted quench method into a salt bath at temperatures ranging from 450 to 210°C. A TTP curve for 7050T76 sheet data has then been used to predict tensile property inhomogeneity in large 7010 forgings with known cooling rates.

Monte Carlo simulation of stretched exponential relaxation near the glass transition

The dynamical behavior of a supercooled polymer melt is studied by means of Monte Carlo simulation. The simulation uses a version of the bond-fluctuation (lattice) model in which long bond vectors are favored energetically. The expansion on the length scale of a bond also induces an increase of the chains' size and stiffness during supercooling. In a dense melt the tendency of an individual chain to stretch has to compete with that of all others. This competition between the internal energy of a chain and the density of the melt strongly slows down the structural relaxation at low temperatures. In order to analyze the dynamical behavior of this model different relaxation functions were calculated in a temperature region ranging from the normal liquid-like to the supercooled state of the melt. Among these relaxation functions are the end-to-end vector correlation function and the correlation function of the Rouse modes. Both functions exhibit a time-temperature superposition property at all times. The corre sponding superposition (relaxation) times can be fitted by a Vogel-Fulcher equation, yielding a common Vogel-Fulcher temperature of about T 0 ≈ 0.12–0.13. As in experiments, this temperature is smaller than the critical temperature of mode-coupling theory (T 0 < T c ≈ 0.15). In addition to this temperature dependence another characteristic feature of the correlation functions is that their relaxation is stretched. For the Rouse modes this stretching is unexpected from the Rouse theory. However, as the theory predicts, the modes remain statically uncorrelated for all studied temperatures.

Press quenching of aluminium alloys

AbstractThe literature concerning press quenching is reviewed and the relevant precipitation kinetics are presented. Such kinetics may be presented on either continuous cooling curve or time–temperature–property diagrams. The homogenisation and subsequent reheating necessary are discussed in terms of microstructure and composition. Thermal considerations include heat transfer occurring both during the extrusion process and cooling after leaving the die. The interaction of extrudability and press quenching is discussed and it is shown that the ultimate solution must be one of compromise. The press effect is shown to be important and some results concerning the press quenching of 2000 series alloys are presented.MST/742