Quench Sensitivity Research Articles

Quench sensitivity and transformation kinetics of high vacuum die casting AlSi10MgMn alloy

AlSi10MgMn alloy high vacuum die castings are being widely used in automotives. T6 heat treatment can increase the casting mechanical properties. In this study, the time-temperature-transformation (TTT) and time-temperature-property (TTP) curves of high vacuum die casting (HVDC) AlSi10MgMn alloy were measured by interrupted quenching method, and the quench sensitivity range of the alloy was obtained. Based on the results, the quench factor analysis (QFA) method was used to predict the mechanical properties of alloy at different cooling rates. The microstructure transformation of the alloy during isothermal process was analyzed by phase transformation kinetics. The results show that the quench sensitivity range is 295–445°C with the nose temperature of 370°C. The phase transformation rate of the alloy at 460°C is higher than that at 280°C based on the results of phase transformation kinetics. The rod-shaped β-Mg2Si phases precipitate during the isothermal process and grow up with the extension of holding time, which Reduce the density of the fine age-induced precipitates β '' and increase the size of precipitate free zones (PFZ) after the followed aging treatment. The critical cooling rate of the alloy should be higher than 7.7°C /s to obtain good comprehensive mechanical properties.

Asymmetric and anisotropic quench sensitivity of ZA81M magnesium alloy

The quench sensitivity of the ZA81M magnesium alloy is studied by combining experiment and crystal plasticity finite element simulation. The quench sensitivity is high in tension and low in compression making the single-valued quench sensitivity calculated from hardness insufficient. So, there is different loss rate of strength, along different test directions of the alloy, due to slow quenching, i.e., the quench sensitivity is asymmetric and anisotropic. The coarsening of the precipitate and widening of the precipitate-free zone are the origin of the quench sensitivity. Crystal plasticity finite element simulation is proposed to calculate the quench sensitivity. The phenomenological constitutive model is used to explicitly consider the strengthening effect of precipitates on different slip and twinning systems. So, the precipitate characteristics of the water-quenched and air-cooled alloy are easily captured. The anisotropy and asymmetry of the quench sensitivity in two perpendicular sample planes are determined by simulation. Such a method can be useful for determining the quench sensitivity of precipitation-hardening alloys with low crystal symmetry and with precipitates having different strengthening efficiencies on different slip or twinning systems.

Quench sensitivity of the extruded Mg-6Zn-0.2Zr/Mg2Si composite: Position dependence and role of dislocation density

The quench sensitivity of the Mg-6Zn-0.2Zr/Mg2Si composite is investigated by microstructure and mechanical properties analysis. It is position-dependent, which is high in the center and low on the surface of the composite. In the center, the mismatch in the CTE between the Mg2Si and Mg matrix leads to high dislocation density in the matrix upon fast quenching, which promotes age hardening. The dislocation density decreases for a lower quenching rate, and leads to lower hardness. Such origin of quench sensitivity is specific to the magnesium composite in addition to the well-recognized solute and vacancy loss. On the surface, low concentration of Zn element leads to low hardness under both cooling conditions. The dislocation and precipitates act as a buffer zone to mitigate the strain incompatibility, which alleviate stress concentration near the Mg/Mg2Si interface. So, the interface debonding is delayed, and twin growth is suppressed. The lower quenching rate negates such a beneficial effect.

Study on Quench Sensitivity during Isothermal Treatment of 7A65 Aluminum Alloy.

The quenching sensitivity of 7A65 aluminum alloy was investigated using interrupted quenching experiments. The time-temperature transformation (TTT) and time-temperature performance (TTP) curves of the alloy were determined. The results indicate that the nose temperature is about 320 °C and the quenching sensitivity temperature range is from 240 °C to 360 °C. During the isothermal treatment, the supersaturated solid solution resolves to the equilibrium phase of η (MgZn2), and the precipitation rate is the largest at about 320 °C. Through transmission electron microscope (TEM) observation and X-ray diffraction (XRD) tests, it was found that with the extension of the isothermal holding time, the originally dispersed η' phase gradually decreases until disappear, and the number of η phase increases and gradually grows up at the grain boundary or around the Al3Zr particles. The rod-like η phase at the grain boundary is distributed from discontinuous distribution to chain-like continuous distribution, and the precipitation free zone (PFZ) is gradually generated and widened as the holding time is extended. At the nose temperature, the driving force of nucleation is high, and the diffusion rate is fast, which promotes the precipitation and growth of η phases. The coarse η phase weakens the mechanical properties. According to the results, it is recommended to increase the cooling rate at the sensitivity temperature range to reduce the precipitation of the η phase and decrease the quenching cooling rate from solution temperature to 360 °C to reduce residual stresses in the components.

Effect of cooling rate on the composition and chemical heterogeneity of quench-induced grain boundary η-phase precipitates in 7xxx aluminium alloys

The mechanical properties and stress corrosion cracking (SCC) resistance of 7xxx series aluminium alloys are significantly affected by the composition and distribution of precipitates formed during heat treatment. In particular, their quench sensitivity is related to the formation of η-phase precipitates that nucleate heterogeneously on grain boundaries at lower cooling rates after solution treatment, which has been a key factor restricting the gauge of hot rolled plates in the aerospace industry. To better understand the effects of slower cooling rates on the composition of quench-induced grain boundary precipitates (Q-GBPs) found in thick plate 7xxx alloys, plasma focused ion beam and high-resolution scanning transmission electron microscopy were used to obtain accurate composition data. The η-phase Q-GBPs have a complex- branched morphology, which develops higher aspect ratios and secondary arms as the cooling rate is reduced. Only a small change in average composition of Q-GBPs was found with cooling rate; but a large scatter was observed. This is caused by significant Zn/Cu/Al composition gradients developing along their principal growth directions in both AA7050 and AA7085 alloys. This concentration gradient did not reduce significantly after a T76 treatment. Simulations of Q-GBP growth with different cooling rates using a CALPHAD-informed phase-field model, with the η-phase represented by a two-sublattice model, gave results consistent with experimental observations. Chemical gradients were predicted to develop in the Q-GBPs due to the changing local equilibrium at the growth front during the cooling. The influence of this non-homogeneous microchemistry on the SCC behaviour of 7xxx alloys is briefly discussed.

Effects of V addition on microstructure and pseudoelastic response in Fe–Mn–Al–Ni alloys

Avoiding quench cracks and controlling the formation process of NiAl precipitates are essential to regulate the microstructure and pseudoelastic properties of Fe–Mn–Al–Ni shape memory alloys (SMAs). In this study, we investigated the effect of 1.5 at.%V addition on the quench sensitivity of Fe–Mn–Al–Ni SMAs and the precipitation behavior of NiAl precipitates in air-cooled Fe–Mn–Al–Ni–V SMAs. It is found that the V addition significantly inhibits the precipitation process of non-transforming γ-phase. Polycrystalline sample of bamboo structure was prepared by abnormal grain growth and tested by incremental strain cycling tensile test at room temperature. The polycrystalline Fe–Mn–Al–Ni–V SMAs obtain fully reversible thermoelastic martensitic transformation without quenching, which also prevents the formation of quenching cracks. Single crystal samples were further prepared by directional recrystallization. High number-density and relatively large-size coherent β-NiAl precipitates were obtained to strengthen the matrix in the single crystal without aging, resulting in large stress hysteresis and irrecoverable strain. After aging Fe–Mn–Al–Ni–V single crystal for 3 h at 200 °C, both the stress hysteresis and irrecoverable strain decreased, thereby achieving good pseudoelasticity in Fe–Mn–Al–Ni–V SMAs.

Influence of Cu content on the hardenability of Al-xCu-1.1Li alloys

The influence of Cu content (3.7 wt%, 4.1 wt% and 4.3 wt%) on the hardenability of Al-xCu-1.1Li alloys was evaluated through a novel end quenching method by using cold-rolled thin sheets combined with strength measurement after subsequent T8 aging. The yield strength of all three aged alloys decreases with the increase of the distance away from the quenching end. The quenching depth decreases with the increase of the Cu content, which was described by the distance of 95% strength retention value of the samples at the quenching end. The intragranular coarse Cu-enriched phase particles formed during the end quenching process impede the precipitation of T1 precipitates and then lead to the strength reduction. The higher Cu content alloy with more and larger Cu-enriched particles inside the grain causes the more decrease in T1 precipitation, which consequently leads to more reduction in strength. The alloy with higher Cu content therefore has lower quenching depth. The coarse Cu-enriched grain boundary phase particles cause the solute depletion around the grain boundary and create PFZ. Based on the time-temperature-properties (TTP) curves, the quench sensitivity increases and the stability of the supersaturated solid solution of the alloy decreases with the rise of the Cu content. Additionally, the coarse Cu-enriched particles within the grain might be coarse Al2Cu particles, which tend to nucleate at the Al3Zr particles.

A comparative study on precipitation behavior of a sand-cast Al–Li–Cu alloy with the different quenching rates

The performance of large-size structural components with varied wall thickness is mainly determined by the quench sensitivity, while there was a blank of the studies on the quench sensitivity of cast Al–Li alloys. In this study, the precipitation behavior of sand-cast Al–2Li–2Cu-0.5Mg-0.15Sc-0.15Zr-0.05Ti alloy subjected to different quenching conditions in room temperature water, boiling water and air was compared. The effect of the quenching rates on the formation mechanisms of δ΄ (Al3Li) and T1 (Al2CuLi) precipitates was discussed. It was found that a rapid quenching rate facilitated the precipitation of T1 phases and the refinement of δ′ phases, which contributes to the improvement of the mechanical properties. During the subsequent ageing, the strength and ductility were enhanced with the quenching rate increasing, but the strength did not vary by more than 15%, indicating that the sand-cast Al–Li–Cu alloy owns a lower quench sensitivity. This work is expected to enlighten the understanding of the evolution mechanisms of precipitates during quenching and provide a reference for the heat treatment of complex structural components for cast Al–Li alloys.

Decreased dislocation density as an origin for the quench sensitivity of the Al-Si-Mg alloys with high Si content

The effect of Si content on the quench sensitivity of the Al-Si-Mg alloys was investigated by conducting the age hardening test of the alloys with different cooling rates after solution heat treatment. The quench sensitivity increases with increasing Si content in the range of 2–12%. The microstructure shows that, apart from the solute loss to the dynamic precipitates with low hardening ability, the decrease in the dislocation density induced by the thermal stress at a low cooling rate contributes to enhanced quench sensitivity by lowering the density of heterogeneous nucleation sites for precipitates. The quench sensitivity map is constructed, it relates the decrease in the peak hardness to the average cooling rate and the strain energy stored in the aluminum matrix due to the mismatch of thermal expansion under the assumption of pure elastic deformation. The effect of the microstructure characteristics, including the size, fraction and shape of Si on the quench sensitivity can be accounted for by the latter parameter. • The quench sensitivity of the Al-Si-Mg alloy increases with increasing Si content. • The decreased dislocation density is an origin of the quench sensitivity. • Quench sensitivity map considering the dislocation density change is constructed.

Coatings Sensitivity to the Quench Marks

During tempering process, the non-homogenous heating or rapid cooling can induce localized strain in the glass leading to birefringence (or optical anisotropy) phenomenon, a result of the photoelastic effect. Since transmission and reflection coefficients of interfaces at high angles can be quite different with the polarization, inhomogeneous birefringence may manifest as peculiar geometric patterns of bright or darkish shadows or iridescence effects in given polarized observation conditions. The patterns appearance may be at the origin of dispute between the client and the glass manufacturer. Each party may have a different perception, how strong the anisotropies are and what is permissible. With the use of an in-line scanner for the optical retardation, it is possible to control and optimise the tempering process homogeneity and thus reduce the visibility of the patterns. However, the presence of low emissivity coatings on the façades windows can alter the visibility of the quench marks: depending on the coating nature, the quench pattern visibility can be magnified or reduced. Here, we show the calculation of σQM, as a parameter representing the coating sensitivity to quench marks, i.e., the capability of a coating to reveal or hinder the iridescence pattern of tempered glass. Thanks to the angular measurements of the transmission and reflection in s and p polarization we compute the quench mark sensitivity by estimating a color contrast gradient with regard to the phase delay.

Enhancing the mechanical performance of Al–Zn–Mg alloy builds fabricated via underwater friction stir additive manufacturing and post-processing aging

• This is the first time to report that in-process water cooling can effectively solve the macro-scale and local softening problems in the FSAM of the age-hardenable Al–Zn–Mg alloy. • Homogeneous microstructures and mechanical properties are obtained in the underwater FSAM build. • After natural aging, the UTS of the water-cooled build is slightly higher than that of the base metal. • The underlying mechanism of the improved mechanical properties correlated with microstructure developed during FSAM process is discussed and clarified. Our previous studies have demonstrated that underwater friction stir additive manufacturing (FSAM) could effectively suppress the macroscale softening of the fabricated Al–Zn–Mg–Cu alloy build from top to bottom. However, the accompanying local softening problem, i.e., a low-hardness region at the bottom of each stir zone, becomes prominent. In this study, an Al–Zn–Mg alloy with low quench sensitivity was used to fabricate a multilayered build via underwater FSAM. In-process water cooling could effectively solve the macroscale and local softening problems in the FSAM of the Al–Zn–Mg alloy and improve the mechanical performance of the build. The microhardness and ultimate tensile strength (UTS) of the water-cooled build in as-fabricated and aged states were more uniform along the building direction and higher than those of their counterparts. After 90 days of natural aging, the UTS of the water-cooled build in building and traveling directions reached 398 and 400 MPa, respectively, slightly higher than that of the base metal (392 MPa). The enhancement in the mechanical performance of the water-cooled build was attributed to a high degree of supersaturation and age-strengthening ability because of a high cooling rate of the underwater FSAM process and low quench sensitivity of the base metal.

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.

Effect of homogenization temperature on microstructure and mechanical properties of Al-Mg-Si alloy containing low-melting point elements

To evaluate the effect of homogenization conditions on the possible loss of low-melting-point Pb and Bi to the surface in the free-cutting AA6026 alloy, three homogenization regimes were applied: 480 °C/12 h, 530 °C/12 h, and 550 °C/6 h. The microstructural characterization by optical, scanning, and transmission electron microscopy coupled with EDS analysis, macroanalysis of chemical composition by ICP-AES as well tensile tests at room and 500 °C, and Charpy impact test were employed to evaluate the different homogenization regimes. It was found that the choice of homogenization temperature had no significant effect on the level of loss of low-melting point elements. The optimal homogenization regime appeared to be 550 °C/6 h as it led to almost complete β-AlFeSi → α-AlFe(Mn)Si transformation and β-Mg2Si dissolution resulting in improved mechanical properties. The presence of the liquid phase did not lead to catastrophic failure due to the liquid metal embrittlement of the aluminum matrix, but the wetting of Fe,Mn – bearing constituents by molten Pb led to decohesion of the constituents. The morphological change to globular α-AlFe(Mn)Si decreased the surface area and interconnectivity of the microconstituents, which improved the hot ductility. During cooling after homogenization at T > 500 °C, the Q-phase precipitated, pointing up the potential quench sensitivity of the alloy. However, precipitation of the Q-phase laths in dispersoid-free zones reduced strain localization and improved room temperature ductility and impact toughness.

The Microstructure Evolution and Electrochemical Corrosion Behavior of 7A46 Aluminum Alloy in Different Quenching Conditions.

The quenching condition of aluminum alloy can affect the mechanical property and corrosion resistance of the profile. This paper is aimed at the low quench sensitivity of aluminum alloys. Scanning electron microscopy and transmission electron microscopy were used to analyze precipitate behaviors of the 7A46 aluminum alloy under different isothermal cooling conditions and microstructure evolutions of quench-induced precipitations. The effect of the different isothermal time on the corrosion resistance of the alloy, and the relationship between microstructure and corrosion resistance after quenching were revealed through electrochemical impedance spectroscopy and potentiodynamic polarization tests. Results show that corrosion sensitivity of the quenching-aged alloy is much higher than that of the double-aged (DA) alloy, and the corrosion resistance of the quenched alloy decreases firstly and then increases. Due to the high density of the matrix precipitates, the increased content of the impurity element, the discontinuity of the grain boundary precipitates and the widening of the precipitates free zone, the most serious degree of corrosion performance among the quenched alloys is 295 °C at 800 s, and the self-corrosion potential and self-current density is −0.919 V and 2.371 μA/cm2, respectively.

The Influence of the Zn/Mg Ratio on the Quench Sensitivity of Al-Zn-Mg-Cu Alloys

The Influence of the Zn/Mg Ratio on the Quench Sensitivity of Al-Zn-Mg-Cu Alloys

On the extraordinary low quench sensitivity of an AlZnMg alloy

The scope of this work was to investigate the quench sensitivity of a high-purity wrought aluminum alloy Al6Zn0.75 Mg (in this work called 7003pure). This is compared to a similar alloy with the additions of Fe, Si, and Zr at a sum less than 0.3 at.% (in this work called 7003Fe,Si,Zr). Differential scanning calorimetry (DSC) was used for an in situ analysis of quench induced precipitation in a wide range of cooling rates varying between 0.0003 and 3 K/s. In 7003pure, three main precipitation reactions were observed during cooling, a medium temperature reaction with a distinct double peak between 325 and 175 °C and a very low temperature reaction starting at about 100 °C. An additional high temperature reaction related to the precipitation of Mg2Si starting at 425 °C has been observed for 7003Fe,Si,Zr. In terms of hardness after natural as well as artificial aging, alloy 7003pure shows a very low quench sensitivity. Hardness values on the saturation level of about 120 HV1 are seen down to cooling rates of 0.003 K/s. The as-quenched hardness (5 min of natural aging) shows a maximum at a cooling rate of 0.003 K/s, while slower and faster cooling results in a lower hardness. In terms of hardness after aging, 0.003 K/s could be defined as the technological critical cooling rate, which is much higher for 7003Fe,Si,Zr (0.3–1 K/s). The physical critical cooling rates for the suppression of any precipitation during cooling were found to be about 10 K/s for both variants.

Detailed investigation of quench sensitivity of 2050 Al-Cu-Li alloy by interrupted quenching method and novel end quenching method

The quench sensitivity of 2050 Al-Cu-Li alloy was determined by the time-temperature-transformation (TTT) curves and time-temperature-property (TTP) curves based on conductivity and hardness. Additionally, a novel end quenching test was used to investigate the quench sensitivity of cold-rolled sheets with a thickness of 2 mm which cannot be tested by conventional methods. The microstructure evolution during interrupted quenching (IQ) treatment and end quenching test was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The precipitation and coarsening of Cu-rich phases during quenching are the main factors affecting the quench sensitivity of the alloy. Meanwhile, these Cu-rich phases lead to the uneven distribution of precipitates (T1 and θ′), which results in the decreased tensile properties. The influence of precipitate free zones (PFZs) on elongation during end quenching test was clarified and the high quench sensitive temperature zone was found to be 260 ~440 °C. This work can help to optimize the quenching process and improve the mechanical properties of the 2050 Al-Cu-Li alloy.

Effects of nano-sized TiB2 particles and Al3Zr dispersoids on microstructure and mechanical properties of Al–Zn–Mg–Cu based materials

The effects of TiB2 and Zr on the microstructure, aging response and mechanical properties of hot-extruded Al–Zn–Mg–Cu based materials were investigated and compared by multi-scale microstructure characterization techniques. The results showed that proper addition of TiB2 particles could refine grain size during solidification, promote dynamic recrystallization during extrusion, and inhibit grain growth during solution treatment. Meanwhile, Zr addition had minor influence on the grain refinement during solidification, but could effectively suppress recrystallization and grain growth compared with the Zr-free alloy. Furthermore, the TiB2 addition could simultaneously enhance the aging kinetics and peak-aged hardness of the materials. Comparatively, Zr addition could also improve the peak-aged hardness with minor effect on the aging kinetics of the materials. Finally, the quench sensitivity, elastic modulus and tensile properties of the materials were compared and studied. Specifically, the relationship between the microstructure and mechanical properties, and the strengthening mechanisms were discussed in detail.

Investigation of Quench Sensitivity and Microstructure Evolution During Isothermal Treatment in 2195 Al–Li Alloy

Investigation of Quench Sensitivity and Microstructure Evolution During Isothermal Treatment in 2195 Al–Li Alloy

Effects of the coherency of Al3Zr on the microstructures and quench sensitivity of Al–Zn–Mg–Cu alloys

Effects of the coherency of Al3Zr on the microstructures and quench sensitivity of Al-8.3Zn-2.3Mg-2.4Cu (AA7055) alloys were investigated. These alloys were subjected to two cold-rolling ratios (i.e., 5% and 20%) in order to vary the coherency of Al3Zr particles. The main objectives of this study were to reduce the quench sensitivity, refine the grain size, and retain the coherency of Al3Zr for high-strength Al–Zn–Mg–Cu production alloys. Results reveal that with the increase in the cold-rolling ratio, the quench sensitivity of the Zr-containing alloys increases. At a high cold-rolling ratio, the interface between Al3Zr particles and the matrix became semi-coherent after solution treatment. This semi-coherent interface led to the heterogeneous nucleation of solute atoms during quenching, which was the leading cause for the high quench sensitivity. By contrast, at a low cold-rolling ratio, the alloys did not exhibit any noticeable quench sensitivity. The Al3Zr particles retained coherence in the matrix and did not afford heterogeneous nucleation sites. On the other hand, regardless of the cold-rolling ratio, the alloys without Zr did not exhibit a high quench sensitivity. However, from the electron backscatter diffraction (EBSD) analysis, the grain size became coarser, and the recrystallization fraction was higher for alloys without Zr.