Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/043—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with silicon as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent

Definitions

• the present invention relates generally to the heat treatment of aluminum-based molding alloys containing silicon, as well as the resulting molded parts.
• Aluminum-based molding alloys have different families of composition, most of which are suitable for structural hardening by heat treatment.
• All these alloys are widely used for the mass production of automotive components, for example cylinder heads subjected to very high stresses in service. In order to maximize the mechanical properties of these alloys, it is customary at least for the most severe cases of stress, to carry out a heat treatment having a dissolution and a quenching, followed by a structural hardening income.
• a disadvantage of this type of treatment is that it can make the alloy extremely difficult to machine, and this in particular in the case of alloys with structural hardening comprising little or no copper (typically at contents lower or equal to 1 %).
• Document EP-A-1 065 292 discloses a process aiming to carry out, after dissolving a part made of light alloy, which can be assimilated to stepped quenching, by immersion in a salt bath so as to quickly bring the room temperature to a value between 350 and 450 ° C.
• Such a known method has the effect of increasing the tensile strength of the material of the part at high temperature, but does not in any way solve the problems of aptitude for machining.
• this process leads to losses of mechanical characteristics at room temperature which are unacceptable for cylinder head type applications of a combustion engine.
• the present invention aims to overcome these drawbacks and to make it possible to obtain foundry parts having a good compromise between the intrinsic performances which are required of them, in particular as regards resistance to different types of stresses, and their aptitude for machining and deburring after machining.
• a method of heat treatment of a foundry part made of aluminum alloy, in particular of aluminum, silicon and magnesium alloy, and if appropriate of copper characterized in that it includes the following steps:
• the second temperature range is chosen so that the treated alloy has a tensile strength reduced by about 10%) to 40%, and preferably from about 15% to 35%, compared to the tensile strength which would be obtained with a single dissolution in the first temperature range and for a period equal to the first and second cumulative durations.
• the second temperature range is lower than the first temperature range by approximately 8 to 14%.
• the first temperature range is between approximately 510 ° C and 550 ° C, and preferably between approximately 520 ° C and 540 ° C.
• the first duration is then between approximately 1 hour and 4 hours, and preferably between approximately 1 hour and 2 hours.
• the second temperature range is then between approximately 455 ° C and 485 ° C, and preferably between approximately 460 ° C and 480 ° C.
• the second duration is then between approximately 1 hour and 5 hours, and preferably between approximately 1 hour and 3 hours.
• step (b) The duration of step (b) is then between approximately 0:30 and 3:30, and preferably between approximately 1 hour and 2:30.
• the present invention provides a foundry piece of aluminum-based alloy, in particular of aluminum, silicon and magnesium alloy and optionally of copper, with in particular a copper content of less than about 1 % by weight, with improved machinability, characterized in that it has:
• the figurel illustrates the microstructure of a first type of alloy treated according to the prior art
• FIG. 2 illustrates the microstructure of this same type of alloy treated according to the present invention
• FIG. 3 illustrates the microstracture of a second type of alloy treated according to the present invention
• - Figure 4 illustrates the microstructure of this same type of alloy treated differently from the present invention
• - Figure 5 is a diagram of mechanical properties strength / elongation illustrating the properties obtainable according to the invention.
• a heat treatment according to the invention is carried out by dissolving at two temperature levels.
• a first stage is carried out in a range of high temperatures, that is to say in the usual temperature range for dissolving the alloys considered that those skilled in the art will define according to well known references.
• this first temperature is between approximately 510 ° C and 550 ° C, preferably between approximately 520 ° C and 540 ° C, and more particularly around 530 ° C .
• this temperature will be lower, for example between around 475 ° C and 515 ° C, and preferably around 495 ° C for copper contents of 2 to 3% by weight.
• this first level is limited to durations of the order of 1 h to 4 h, preferably 1 h to 2 h, knowing that an extension of this level does not lead to significant improvements in the final properties of the material.
• This first stage is followed by a second stage of dissolving in a second lower temperature range.
• this second temperature range is between approximately 455 ° C and 485 ° C, preferably between approximately 460 ° C and 480 ° C, and more preferably around 465 ° C (it being specified that for an alloy with a copper content of 2 to 3% by weight, this second temperature range will advantageously be between 425 ° C and 455 ° C, and more preferably around 450 ° C). More generally, the second temperature range is about 8-14% lower than the first temperature range.
• the duration of this second stage is of the order of 1 to 5 hours, preferably 1 to 3 hours.
• the cooling between the two stages of dissolution is carried out so as to progressively pass from the highest temperature to the lowest temperature over a period of between 30 minutes and 3 hours 30 minutes. Preferably, and here again for mainly economic reasons, this duration is between 1 hour and 2 hours 30 minutes.
• quenching is applied according to the usual conditions, for example quenching with water.
• an income is produced intended to develop the hardening precipitation of the alloy.
• This income can be chosen in the usual ranges of temperature and duration; depending on the properties sought, it may be an under-income, an income at the peak of resistance or an over-income.
• the temperature of the second dissolution stage makes it possible for the tensile strength properties of the alloy thus treated to decrease by approximately 10 to 40%, and preferably by around 15 to 35%, relative to the properties which would be obtained with a single solution treatment at the first temperature and for a period equal to the cumulative durations of the two stages (including the cooling phase from the first stage to the second stage), and keeping the same quenching and tempering conditions.
• the aim is to achieve, compared to a conventional single-stage heat treatment, an improved compromise between the properties of tensile strength, elongation and quality index. More particularly, it has been found that it is preferable to be placed in the zone of reduction of properties from 15 to 35% if it is wished to optimize the resistance / elongation compromise while benefiting from an improved machinability.
• this two-stage solution reduced very significantly the residual stresses present in the part after the end of the heat treatment. This can have advantages significant on the behavior of parts, especially cylinder heads of combustion engines, very highly stressed.
• the typical microstructure after the usual heat treatment reveals: - a silicon globulated by the stay at high temperature, as shown in Figure 1 of the drawings, and - an optimal dissolution, that is to say that no Mg2Si compound is not observed out of solution.
• a heat treatment comprising dissolving at a first temperature level of 530 ° C for 2 hours then at a second level of 465 ° C for 2 hours , leaving the charge 1 hour to go from the first temperature to the second, then quenching with water at 90 ° C and an income of 5 hours at 200 ° C.
• the breaking strength, the elastic limit and the hardness, with the treatment according to the invention decrease from 20 to 32%. This decrease is in favor of a very strong increase in plastic elongation (that is to say elongation at break) (+ 114%).
• the heat treatment according to the present invention reveals the presence of globulated silicon by dissolving at high temperature, as illustrated in FIG. 2 of the drawings, while obtaining the reduction in resistances or hardness compared to the conventional solution.
• the dissolution at 530 ° C was carried out for 2 hours, and the dissolution at 450 or 400 ° C depending on the case was carried out for 3 hours, with a duration of 90 or 120 minutes to reach the second temperature.
• the dissolving was followed by quenching with water at 90 ° C. and tempering for 5 hours at 200 ° C.
• the solution heat treatment was carried out with two stages according to the invention, as well as a solution treatment with a single stage at the temperature of 465 ° C.
• the stay at high temperature causes the silicon to globulate, as shown in FIG. 3, while in the second case there is no globulization, as shown in FIG. 4.
• the mechanical characteristics are also affected by the type of dissolution carried out, being better after a two-stage dissolution.
• FIG. 5 of the drawings represents the compromises between the mechanical strengths (tensile strength Rm and yield strength Rp at 0.2% deformation, in MPa) and the elongation at break (in%) after heat treatment in one or two stages, depending on the temperature of the single stage or that of the second stage.
• the squares (case of the invention) and the triangles (in the case of a single-stage heat treatment) correspond to different temperatures, as indicated.
• the trajectory in solid line T1 shows the evolution of the torque (resistance to rupture, elongation) as a function of the second temperature of a two-stage solution
• the trajectory in solid line T2 shows the evolution of the same characteristics as a function of the temperature of a solution at a single level
• the dotted trajectory T3 shows the evolution of the torque (elastic limit, elongation) as a function of the second temperature of a two-stage solution
• the dotted trajectory T4 shows the evolution of the same characteristics as a function of the temperature of a solution at a single level.
• FIG. 5 is also shown in connection with the curves T1 and T3 obtained according to the invention, the decreases of 10% and 40% of the resistance corresponding to a field of the invention, as well as the decreases of 15% and 35% corresponding to a particularly preferred area (hatched area) of the invention.
• FIG. 5 shows, from the relative positions of the curves T1 and T3 with respect to the curves T2 and T4, respectively, that a two-step solution treatment presents a compromise strength / elongation at break greater than the same material subjected to a heat treatment at a single level, regardless of the temperature level of this single level.

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• 2002
  • 2002-03-20 FR FR0203530A patent/FR2837501B1/fr not_active Expired - Lifetime
• 2003
  • 2003-03-20 WO PCT/FR2003/000887 patent/WO2003078674A2/fr not_active Application Discontinuation
  • 2003-03-20 AU AU2003240929A patent/AU2003240929A1/en not_active Abandoned
  • 2003-03-20 US US10/508,227 patent/US7776168B2/en not_active Expired - Lifetime
  • 2003-03-20 EP EP03730296.5A patent/EP1488021B1/de not_active Expired - Lifetime

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