Process for solidifying slowly quenched / cooled cast aluminum components

Abstract

A method for improving the mechanical properties of a heat-treatable aluminum alloy used in engine blocks, cylinder heads, transmission housings and / or suspension components, comprising: Heat treating the aluminum alloy at a solution treatment temperature for the aluminum alloy for a first period of time; Heating the heat-treated aluminum alloy to a temperature of 5 °C to 30 °C above the solution treatment temperature; Cooling the heated aluminum alloy; Pre-hardening of the cooled aluminum alloy at a temperature in the range of 65 °C to 95 °C and Hardening the pre-hardened aluminum alloy at a hardening temperature above the pre-hardening temperature.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to methods and technologies that improve the tensile properties of aluminum alloys, and more particularly to heat-treatable cast aluminum alloys or cast aluminum alloys that have been slowly cooled / quenched after solidification and / or solution treatment to minimize residual stresses and distortion. BACKGROUND OF THE INVENTION

[0002] Thermal quenching is important in the heat treatment processes of metal objects. For age-hardenable materials, such as many cast aluminum alloys, thermal quenching helps develop a supersaturated solid solution for subsequent precipitation hardening. Higher supersaturation typically leads to improved mechanical properties (especially yield strength) through subsequent age-hardening / precipitation hardening processes. The degree of supersaturation of solidifying elements in a solid solution after quenching depends strongly on the quenching rate. Rapid quenching / cooling typically results in high solute supersaturation. As a result, the material is often quenched in cold or warm water to maximize solution supersaturation.

[0003] Many metal parts, such as engine blocks and cylinder heads, have complex shapes and varying wall thicknesses. A significant amount of residual stress and distortion can develop in the metal parts, even when quenched in warm or boiling water. If a tight tolerance is required for part manufacturing, resulting distortion can be expensive and difficult to correct. While performance is an important factor in reducing residual stresses, achieving distortion reduction during machining is another incentive.

[0004] One approach to reducing the difference in cooling rate between different sections of a part is to use a milder quenching medium, such as hot / boiling water, water-polymer or polymer solutions, or even forced air quenching. Although air quenching is one of the most effective ways to reduce residual stresses and distortion, it can dramatically reduce the mechanical properties of the final product. Fig. 1 shows an example of a significant reduction of residual stress in a cylinder head with air quenching compared to water quenching. Fig. Figure 2 shows an example of the reduction of tensile properties during quenching in air.

[0005] DE 10 2008 046 803 A1, DE 10 2008 056 511 A1,

[0006] WO2006 / 066314 A1, CN 1 834 281 A and AU000006111169A each deal with the topic of thermal quenching in heat treatment processes for metal objects.

[0007] The object of the present invention is to provide a method for improving the mechanical properties of cast aluminum components or cast aluminum components, wherein the cast aluminum components or cast aluminum components are slowly quenched / cooled after a solution heat treatment and / or solidification. SUMMARY OF THE INVENTION

[0008] This object is achieved by the subject matter of independent claim 1. Methods and technologies are provided to maximize the hardening response and mechanical properties of aluminum alloys. These methods are applicable to all hardenable aluminum alloys, both wrought and cast aluminum alloys.

[0009] A method according to the invention for improving the mechanical properties of a heat-treatable aluminum alloy used in engine blocks, cylinder heads, transmission housings, and / or suspension components comprises the following steps: heat-treating the aluminum alloy at a solution treatment temperature for the aluminum alloy for a first period of time; heating the heat-treated aluminum alloy to a temperature of 5°C to 30°C above the solution treatment temperature; cooling the heated aluminum alloy;

[0010] Pre-hardening the cooled aluminum alloy at a temperature in the range of 65 °C to 95 °C and hardening the pre-hardened aluminum alloy at a hardening temperature above the pre-hardening temperature.

[0011] Thus, the improved hardening process for the slowly quenched / cooled aluminum alloys includes, but is not limited to, at least two-stage solution treatment and two-stage age hardening. In solution treatment, the components are first heat treated at an initial solution treatment temperature for the alloy (about 5 to 10°C below solidus) and then gradually heated to about 5°C to about 30°C above the initial solution treatment temperature for the material. The temperature increase during solution treatment can be in stages, in a continuous manner, or combinations thereof. The temperature change profile can be determined and optimized based on thermodynamics and kinetics. For hardening treatment, the castings / components are first heat treated at a lower temperature compared to thethe subsequent cure(s), typically cured between about room temperature and about 100°C. The preferred pre-cure temperature is between about 65°C and about 95°C. The pre-cure time varies with the pre-cure temperature and can be as long as several days or weeks if the parts are first naturally cured at room temperature. The subsequent curing steps are generally carried out at temperatures above about 100°C, for example, between about 140°C and about 240°C, with the preferred temperature being between about 165°C and about 200°C. The temperature change in the subsequent curing process can occur in stages, in a continuous manner, or in combinations thereof. The temperature change profile can be determined and optimized based on thermodynamics and kinetics.The subsequent curing time in each stage varies from about 1 to about 10 hours, with the preferred total subsequent curing time being between about 4 and about 8 hours.

[0012] In another embodiment, a method for improving the mechanical properties of a heat-treatable aluminum alloy is provided. The method comprises at least a two-stage hardening process. There is a pre-hardening stage in which the aluminum alloy is pre-hardened at a temperature ranging from about room temperature to about 100°C, and a non-isothermal hardening stage at a hardening temperature above the pre-hardening temperature. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a comparison of the residual stress distribution in a cylinder head. Fig.Figure 2 is a comparison of the tensile properties of a cast aluminum alloy quenched in water and air. Fig. Figure 3 is a schematic of one embodiment of a multi-stage solution and hardening process for slow-quenched cast aluminum components. Fig. Figure 4 is a schematic representation of an embodiment of a multi-stage solution treatment. Fig. Figure 5 is a schematic representation of another embodiment of a multi-stage solution treatment. Fig. 6 is a schematic of another embodiment of a non-isothermal solution and step hardening process for slowly quenched cast aluminum components. Fig. Figure 7 is a schematic representation of one embodiment of a multi-stage curing scheme. Fig.Figure 8 is a comparison of the pre-hardening responses of an HPDC alloy (A380) under water quenching and air cooling conditions. Fig. Figure 9 is a graph illustrating the improvement in yield strength of air-quenched A356 + 1% Cu alloy using various embodiments of the multi-stage solution and hardening process. Fig. Figure 10 is a graph illustrating the improvement in yield strength of a weigh-cast and air-quenched A380 alloy using various embodiments of the multi-stage hardening process. Detailed description of the invention

[0013] Hardening produces precipitation hardening by heating the component to a certain temperature and then holding the casting at that temperature for a period of time. Since precipitation hardening is a kinetic process, the solute content in the as-quenched aluminum matrix (solution) plays an important role in the hardening reactions. Mg, Cu, and Si are typical hardening solutes used in aluminum alloys. Mg combines with Si to form Mg / Si precipitates, for example, β''-, β-, and equilibrium Mg. 2 Si phases. The actual precipitate type, amount, and size depend on the hardening conditions. There is a tendency for underhardening to form shearable β'' precipitates, while peak hardening and overhardening conditions form unshearable β' and equilibrium Mg 2Form Si phases. In aluminum alloys, Si alone can form Si precipitates, but these are not as effective at strengthening as Mg / Si precipitates. Furthermore, Cu can combine with Al to form many metastable precipitate phases, for example, θ', θ in Al-Si-Mg-Cu alloys. Similar to Mg / Si precipitates, the actual precipitate type, size, and amount depend on the ageing conditions and alloy compositions.

[0014] To achieve the full benefits of this invention, the aluminum alloys should contain hardening elements (solutes), specifically Mg, Cu, Si, and Zn. The content of the hardening substances should desirably meet certain minimum amounts. The Mg content in the aluminum alloys is advantageously more than about 0.2% by weight, and the preferred concentration is about 0.3% by weight or higher. The copper content is advantageously more than about 0.5% by weight, and the preferred concentration is about 0.8% by weight or higher.

[0015] The Si content in the aluminum alloys is advantageously higher than approximately 0.5% by weight. For cast aluminum alloys or aluminum casting alloys, the preferred Si content is advantageously approximately 5% or higher. Zn is a very important element that reacts with Mg to form MgZn. 2-precipitates at a relatively low temperature (about 75 to about 100 °C). The Zn content is advantageously greater than about 0.3 wt%, and the preferred concentration is about 0.5 wt% or higher.

[0016] The Fig. 3 illustrates an embodiment of a multi-stage solution and hardening process. With the developed techniques, the tensile strengths of the slowly quenched cast aluminum components or cast aluminum components can be increased by at least approximately 10%.

[0017] To maximize the dissolution of solutes during solution treatment, the components are heat-treated in two or more stages. The components are first treated at an initial solution temperature, for example, about 540 °C for A356 alloy and about 490 °C for 310 alloy, for about half the period of the specific solution treatment time. Thereafter, the components are heated to about 5 °C to about 30 °C above the initial solution temperature and held at that temperature for the other half of the specific solution treatment time. In the second stage, a higher temperature is preferred, provided that no incipient melting is produced. Fig. Figure 4 schematically shows an example of the proposed multi-stage solution treatment.

[0018] The solution treatment temperature varies with the alloy and is related to the alloy's solidus. The alloy's solidus can be accurately calculated based on thermodynamics or determined experimentally. In general, the solution treatment temperature should be lower than the solidus to prevent incipient melting. Textbooks and manuals provide solution temperatures for many commercially available alloys. In many cases, the temperatures given in the manual or textbook have been determined experimentally.

[0019] The temperature change during solution treatment does not have to be a step increase. The temperature can be gradually increased based on the alloy melting point change due to the continuous dissolution of low-melting intermetallic phases. For aluminum alloys, solution heat treatment involves the dissolution of intermetallic phases, a reduction in microsegregation, and the fragmentation and spheroidization of second-phase particles. As the solution treatment progresses, equilibrium phases with low melting points are gradually dissolved in the materials, which depends on the diffusion kinetics. As a result, the melting point of the remaining materials becomes high, and the alloy can be gradually heated to a higher temperature, as shown in Fig. 5 is shown.

[0020] The maximum achievable solution treatment temperature at a given time depends on the state of microstructure development and the existence of phases in the materials. The upper limit of the solution treatment temperature, T sol , should not exceed the lowest melting point of the remaining phases. Tsol <Min(T,t,C∈Ω)Tm(T,t.C)(Ω={0<Tsol<Tc;0<t<∞;0<C<C0}

[0021] The temperature can be raised to a point above which incipient melting would occur. The non-isothermal solution treatment temperature profile can be calculated based on computational thermodynamics and kinetics, as well as the initial alloy microstructure and the as-cast microstructure. The non-isothermal temperature profile during solution treatment can be realized in either batch or continuous furnaces. For the continuous furnace, different temperatures can be set in different zones within the furnace.

[0022] An embodiment of solution treatment and air quenching using this approach is described in the Fig. 6 shown.

[0023] In cast aluminum alloys or cast aluminum alloys, the dissolution of the second equilibrium phase during solution heat treatment can be considered a diffusion-driven process. For the dissolution of a spherical precipitate (particle) with a curvature p, the dissolution rate can be determined as follows: drldt=−((Cdi−Cgl)Di(Cpi−Cdi)ri)−(Cdl−CglCpi−Cdi)(Dipt)1 / 2 where r i is the radius of the i-th precipital, C i d is the equilibrium concentration of dissolved substance at the dissolution temperature, C i g is the equilibrium concentration of dissolved substance at the growth temperature, C i p is the concentration of solute in the i-th precipitate, D i is the diffusivity, p is the curvature of the precipitate and c is the dissolution time.

[0024] Equation (2) requires knowledge of the concentration profile of the dissolved substances, which can use the following equation for a multicomponent diffusion, namely ∂Cl(r,t)∂T=∇⋅∑Dij∇Cj(r,t) where C i (r, t) is the concentration of the i-th element at position r and time t, C j(r, t) is the concentration of the j-th element at position r and time t, while Dij represents the diffusion coefficients of the solutes, e.g., Mg, Cu, in the aluminum matrix. Equations (2) and (3) can be solved by iteration. Coarsening of second-phase particles, e.g., Si, occurs either by Ostwald ripening or coalescence, or by a combination of both mechanisms. Ostwald ripening involves mass transfer through the detachment of atoms from smaller structures, followed by diffusion of these atoms through the matrix to attach themselves to the surface of larger structures. The end result of ripening is shrinkage of the smaller structures and growth of the larger structures. The average particle size in the system increases while the number density of the particles decreases. On the other hand, coalescence involves the mixing of two or more particles.For this to occur, the particles must come into contact with each other, and in this case, the driving force is the decrease in surface energy. The most commonly cited description of coarsening is the Liftshitz-Sylozov-Wagner (LSW) description, namely . req3−ro3=89DCoγVatom2tRT where r eq is the radius of the coarsening precipitate and r 0 is its initial radius, D is the diffusivity, R is the universal gas constant, Co is the equilibrium concentration of the coarsening phase, T is the temperature, γ is the surface energy, V atom the atomic volume (m 3 / mol) and t is the coarsening time (IM Lifshitz and VV Slyozov, Phys. Chem. Solids, Vol. 19 (1961), 35, C. Wagner, Z. Electrochem., Vol. 65 (1961), 58.)

[0025] The amount of dissolved elements that decreases during slow cooling / quenching after solution treatment and / or solidification due to the formation of precipitates can be determined using the Quench Factor Analysis (QFA) approach (W. Evancho, J.T. Staley, Metallurgical Transactions, Vol. 5, pp. 43-47, 1974). The assumptions behind Quench Factor Analysis include that the precipitation reaction during quenching is additive, and the reduction in strength (after hardening) can be related to the reduction in solid solution supersaturation during quenching.

[0026] The amount of precipitates formed during slow quenching / cooling after solution treatment and / or solidification can be determined by a unitless variable of the microstructural state, S. dSdt=Seq−Stc, where S eqis the maximum amount of precipitates that is formed in an equilibrium state (for an arbitrarily long isothermal holding) at a temperature during cooling. The value of S eq can be Seq=1−exp[ΔHR(1K4−1T)]; T≤K4 can be calculated, where k 4 is the solvus temperature and ΔH is the precipitation enthalpy for a quench precipitate.

[0027] In equation (5) t c the critical temperature at which the precipitates begin to nucleate and grow, and it is given by: tc=K2 exp[K3K42RT(K4−T)2+K5RT] where K 2 is a constant that refers to the reciprocal of the number of nucleation sites; K 3 is a constant that refers to the energy required for heterogeneous nucleation (J / mol); K 4 is a constant related to the solvus temperature; K 5is a constant related to the activation energy for diffusion (J / mol); R is the universal gas constant, 8.31443 J / (K mol), and T is the absolute temperature (K).

[0028] The numerical algorithm for determining the increase in i-precipitate in a given time step j during quenching is given by ΔSij=(Seq−Si,j−1)[1−exp(−Δtijtcij)] specified.

[0029] At the end of quenching, the total amount of i-th precipitates S I : Si=∑jΔSij

[0030] For each quench precipitate, the coefficients can be calibrated using experimental data of mechanical properties and temperature profiles during quenching. Table 1 shows the coefficients developed for aluminum alloy A357. Table 2 shows the coefficients developed for aluminum alloy A356 + 1% Cu. K 4 , K 5and ΔH were calculated from thermodynamics. It is emphasized that K 3 for Si is 0, which makes the curve for effectively pure growth. Table 1. Coefficients for the A 357 deterrence model K 2 (s) K 3 (J / mol) K 4 (°K) K 5 (J / mol) k (MPa) ΔH (H / mol) OYSmax (MPa) Si particle growth 5,28 × 10 -6 0 813 125200 37,4 60000 301 β on Si particles 6.80 × 10 -9 354 813 119812 92,5 53066 β in the matrix 6,24 × 10 -11 1439 813 119812 126,1 53066 Table 2. Coefficients for the A356 + 1% Cu quenching model K 2 (s) K 3 (J / mol) K 4 (°K) K 5 (J / mol) k (MPa) ΔH (H / mol) OYSmax (MPa) Si particle growth 5,28 × 10 -6 0 813 125200 37,4 60000 294 β in the matrix 6.24 × 10 -11 1439 764 119812 126,1 53066 θ in the matrix 723 212200

[0031] The hardening process for aluminum alloys involves the formation of GP zones and coherent and incoherent precipitates, which is consistent with nucleation, growth, and coarsening of precipitates. To maximize the number density of vacancies and, in particular, to initiate a large number of GP zones in the as-quenched cast aluminum alloy components / parts, pre-hardening of the materials at lower temperatures, followed by one or more hardening steps at higher temperatures, has been discovered. Fig.Figure 7 schematically shows one embodiment of a three-stage hardening scheme. The hardening temperature and hardening time for each stage depend on the alloy compositions and productivity requirements. It should be emphasized that the heat-treated components do not necessarily need to be cooled to room temperature between hardening stages, although they can be if desired.

[0032] The pre-cure stage is designed to create multiple GP zones and fine precipitate nuclei. The variation in precipitate density (number of precipitates per unit volume) is directly related to the nucleation rate, which depends on the curing temperature and time. For aluminum alloys, such as A356, A319, and A380 and their variants, the pre-cure temperature will generally vary from room temperature to approximately 100°C, although it can be higher or lower if desired. Since the nucleation and formation of GP zones and / or fine precipitates are kinetic processes, a longer cure time is expected for a lower cure temperature. For example, if the parts are naturally cured or age-hardened at room temperature, the cure time can be as long as several days or even several weeks. Fig.Figure 8 compares the hardening responses of tensile specimens (12.85 mm in diameter) made of A380 alloy cast in permanent mold and pre-cured at room temperature and 95 °C.

[0033] Subsequent hardening after pre-hardening is designed to maximize the tensile strength of slowly quenched aluminum components. Subsequent hardening may include, but is not limited to, one or more isothermal hardening stages. Hardening temperatures in subsequent hardening stages are generally maintained above approximately 100°C and are typically between approximately 140°C and approximately 240°C for most aluminum alloys and their variants. The preferred hardening temperature range is between approximately 165°C and approximately 200°C. If high productivity and a short hardening time are desired, a higher hardening temperature, for example, approximately 200°C, can be used. Otherwise, a slightly lower hardening temperature, for example, approximately 180°C, is recommended for higher tensile strengths.For an HPDC alloy (A380), one of the optimal hardening schemes is pre-hardening at approximately 95 °C for about 2.5 hours, followed by a two-stage hardening at approximately 180 °C for about 4 hours and approximately 200 °C for about 1 hour.

[0034] The Fig.Figure 9 shows experimental results of a multi-stage solution and hardening process for A356 + 1% Cu alloy. For the same solution treatment conditions (either one-stage or two-stage and multi-stage solution treatment), multi-stage hardening can increase the yield strength by 5 to 10%. It should be emphasized that the Zn content in A356 is less than 0.1 wt%. When the alloy had a higher Zn concentration (e.g., > 0.5 wt%), the tensile properties could be further improved, especially when the materials were slowly quenched / cooled after solution treatment and / or work strengthening. For the same hardening cycle, multi-stage solution treatment can also improve the tensile properties by 5 to 10%.

[0035] The Fig.Figure 10 shows experimental results of multi-stage hardening cycles applied to an as-cast and air-cooled A380 (0.35 wt% Mg) alloy. As expected, the yield strength can be steadily increased by performing the techniques in this invention individually. The multi-stage solution treatment and hardening process can increase the yield strength by at least 10%.

[0036] The tensile properties of slow-quenched aluminum alloys can be as good as those of fast-quenched alloys, while residual stresses and distortion are much lower. The tensile strengths of slow-quenched alloys can be increased by at least 10% compared to alloys using a conventional hardening process.

[0037] The improved tensile properties of slow-quenched aluminum alloys (with minimal residual stress) increase their durability and broaden their acceptance and use in critical structural applications, such as engine blocks, cylinder heads, transmission housings, and suspension components. It could also result in a significant reduction in warranty costs for cast aluminum components in automotive applications.

[0038] The temperature change during the subsequent curing process can occur in stages, continuously, or in combinations thereof. The temperature change profile can be determined and optimized based on computational thermodynamics and kinetics.

[0039] The yield stress of a heat treatable aluminum alloy after hardening can be expressed as σys=σys−Al+σdisp+σq−ppt+σa−ppt+σss be determined, where σ ys-Althe yield stress of pure aluminum is (about 15 MPa), σ disp the increase in yield strength by dispersive particles of the second phase (eutectic), σ q-ppt the change in yield strength due to precipitates formed during quenching is, σ a-ppt the increase in yield strength after quenching by hardening of precipitates, σ ss The increase in yield strength due to solid solution after hardening. In commercial cast aluminum alloys or aluminum casting alloys (e.g., A356, 319, A380, etc.), the increase in yield strength due to eutectic particles can be calculated as: σdisp=C0αμAlfε where ε is the plastic strain, α is the average aspect ratio of eutectic particles, µ A1is the shear modulus of the aluminum matrix, f is the volume fraction of the second-phase (eutectic) particles, and Co is the constant. At 0.2% plastic strain (which is the strain defined to determine the yield strength of the material), the increase in yield strength due to eutectic particles for many cast aluminum alloys is between 10 and 20 MPa (depending on the volume fraction of the second-phase particles in the material).

[0040] The contribution to the yield strength of precipitates during hardening, σ a-ppt, is a combination of shearable and flowing precipitates. Solidification by shearable precipitates (σ ppt-s ) is approximately related to the precipitate volume fraction (f ppt ) and the precipitate radius (r ppt ) by a constant C 1 : σppt_s=C1fpptrppt

[0041] Similarly, the yield strength by bypassing dislocations around non-shearable precipitates σ ppt_b in approximate relation to the precipitate volume fraction (f ppt ) and the precipitate radius (r ppt ) by a constant C 2 : σppt_b=C2fpptrppt

[0042] Equations (12) and (13) can be combined to describe the increase in yield strength to a peak with increasing curing time (while the precipitates are shearable) and the decrease in yield strength with overcuring as the precipitates become larger, non-shearable, and less coherent. Single-peak curing curves can be described by taking the harmonic mean of equations (12) and (13) (HR Shercliff, MF Ashby, Acta Metall. Mater. 38 (1990) 1789): σa−ppt=2σ(t,T)P*161+P*12 where σ(t,T) is the precipitate strength and P* = P|P p. The term P is the temperature-corrected time: P=tTexp(−QΔRT) where t is the curing time, T is the curing temperature, Q A is the activation energy for volume diffusion of atoms through the matrix and R is the gas constant. The parameter P p is the value of P at the peak in the curing curve. Thus, Q A from the slope of a graphical representation of 1n(t p | T) vs 1 / T, where t p the curing time at P p is to be determined.

[0043] The precipitate strength, σ(t,T), can be expressed as a function of curing time (t) and temperature (T): σ(t,T)=(σ0)max[1−exp(−QsR(1T−1Ts))]1 / 2[1−exp(−tτ1)]1 / 2 where the hardening parameter (σ 0 ) max , the solvus enthalpy (Q s ) and the meta-stable solvus temperature (T s) can be determined from the experimental curing data or thermodynamic calculations. The constant (τ 1 ) is represented by the constant K 1 with the curing time corresponding to the peak (t p ) corresponds to: τ1=K1tP

[0044] The contribution of the solid solution to hardening after hardening (σ ss ) in equation (10) varies with the curing time at a given temperature and can be σss=[σssf3 / 2+[σssl3 / 2−σssf3 / 2]exp(−tτ1)]2 / 3 where the indices refer to the initial (σ ssi ) and the final (σ ssf ) hardening contribution of the solid solution. The initial hardening contribution of the solid solution can be calculated from the difference between the as-quenched yield strength (σ aq ) and the intrinsic yield strength ( A1 +σ disp +σ q-ppt ) can be determined: σssi=σaq−σys−Al−σdisp−σq−ppt whereas the final hardening contribution of the solid solution is the difference between the over-hardened yield strength (σ oa ) at the hardening temperature and the intrinsic yield strength (σ ys-A1 +σ disp +σ q-ppt ) is. σssf=σoa−σys−Al−σdisp−σq−ppt

[0045] The over-hardened yield strength (σ oa ) can be calculated from known values ​​of the as-quenched yield strength (σ aq ) and the intrinsic yield strength σ ys-A1 +σ disp +σ q-ppt ) can be determined: σoa=σys−Al+σdisp+σq−ppt+(σaq−σys−Al−σdisp−σq−ppt)exp[−2Qs3R(1T−1Ts)]

[0046] The change in yield strength due to precipitation during slow quenching can be σq−ppt=∑ikiSi12 be determined.

[0047] S i and K i are taken from equation (9) and Tables 1 and 2.

[0048] The solvus enthalpy (Qs ) is used for each curing temperature and use of: Qs=[−R / (1T−1Ts)][ln(1−σ02(σ0)max)] certainly.

[0049] The precipitate strength σ 0 depends on the curing temperature, since the volume fraction of precipitates varies with temperature. σ 0 can be σ0(T)=(σ0)max[1−exp[−QsR(1T−1Ts)]]1 / 2 be calculated.

[0050] It is emphasized that the terms "generally," "usually," and "typically," when used herein, are not used to limit the scope of the claimed embodiments or to imply that particular features are critical, essential, or even important to the structure or function of the claimed embodiments. Rather, these terms are merely intended to identify particular aspects of an embodiment or to emphasize alternative or additional features that may or may not be used in a particular embodiment.

[0051] For the purposes of describing and defining embodiments, it should be noted that the terms "substantially," "significantly," and "approximately" are used herein to convey the inherent degree of uncertainty inherent in any quantitative comparison, value, measurement, or other representation. The terms "substantially," "significantly," and "approximately" are also used herein to convey the degree by which a quantitative representation may deviate from a stated reference without resulting in a change in the basic function of the subject matter.

[0052] Having described the embodiments of the present invention in detail and / or by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the embodiments defined in the appended claims. Although some aspects of embodiments of the present invention have been identified herein as preferred or particularly advantageous, it should be understood that the embodiments of the present invention are not necessarily limited to these preferred aspects.

Claims

[1] A method for improving the mechanical properties of a heat-treatable aluminum alloy used in engine blocks, cylinder heads, transmission housings and / or suspension components, comprising: Heat treating the aluminum alloy at a solution treatment temperature for the aluminum alloy for a first period of time; Heating the heat-treated aluminum alloy to a temperature of 5 °C to 30 °C above the solution treatment temperature; Cooling the heated aluminum alloy; Pre-hardening of the cooled aluminum alloy at a temperature in the range of 65 °C to 95 °C and Hardening the pre-hardened aluminum alloy at a hardening temperature above the pre-hardening temperature. [2] The method of claim 1, wherein the aluminum alloy is maintained at a temperature of 5°C to 30°C above the solution treatment temperature for a second period of time, and wherein the second period of time is approximately the same as the first period of time. [3] The method of claim 1, wherein heating the aluminum alloy to a temperature of 5°C to 30°C above the solution treatment temperature is non-isothermal heating. [4] The method of claim 1, wherein the hardening of the pre-hardened aluminum alloy is non-isothermal hardening. [5] The method of claim 1, further comprising hardening the aluminum alloy at a second hardening temperature, wherein the second hardening temperature is higher than the hardening temperature. [6] The method of claim 1, wherein the curing temperature is in the range of 140°C to 240°C. [7] The method according to claim 1, wherein the aluminum alloy contains at least one of Mg, Cu, Si and Zn. [8] The method of claim 1, wherein the aluminum alloy contains at least one of more than 0.2 wt% Mg, more than 0.5 wt% Cu, more than 0.5 wt% Si, and more than 0.3 wt% Zn.

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