JP6432152B2 - Heat treatment method for aluminum alloy die-casting member - Google Patents

Description

The present invention relates to a heat treatment how the aluminum alloy die cast members. More particularly, the present invention relates to a heat treatment Kata method aluminum alloy die cast members that comprised an Al-Si-Cu alloy.

Conventionally, methods for heat treating age-resistant aluminum alloy high pressure die casting (HPDC) castings have been proposed that obviate the need to use more expensive alternative components.
This heat treatment method is a heat treatment method for a high-pressure die casting of an aging aluminum alloy, and (a) the casting is heated to a temperature at which the solute element can be taken into the solid solution, and the casting is heated to the temperature range. (B) cooling the casting by quenching the casting to 100 ° C. or lower to finish step (a), and (c) bringing the casting into a temperature range that allows natural aging and / or artificial aging. Holding a step of aging the casting after step (b) to achieve a level of solute element solution that allows age hardening without pore expansion in the casting that results in unacceptable blisters in the casting Step (a) is performed (see Patent Document 1).

Special table 2008-525629

  However, in the heat treatment method described in Patent Document 1, since solution treatment is performed at a low temperature for a short time in order to suppress the generation of blisters as much as possible, in the α-aluminum (α-Al) phase of magnesium (Mg) The solid solution diffusion time for copper (Cu) to dissolve in the α-Al phase is not sufficient, and the solid solution of Cu in the α-Al phase is incomplete. There was a problem that the strength was not sufficiently improved.

The present invention has been made in view of such problems of the prior art. The present invention aims at providing while preventing the occurrence of blisters, the heat treatment how the aluminum alloy die cast members that can produce aluminum alloy die cast members having excellent strength.

  The inventors of the present invention have made extensive studies in order to achieve the above object. As a result, it has been found that the above object can be achieved by heating an aluminum alloy die-cast member containing copper (Cu) at a predetermined first heating temperature, and subsequently heating at a predetermined second heating temperature. The present invention has been completed.

That is, the heat treatment method for an aluminum alloy die-cast member of the present invention is a heat treatment method for an aluminum alloy die-cast member made of an Al—Si—Cu alloy, and the first heating temperature at which the volume expansion coefficient is 0.4% or less, a first step of heat treatment at the time, is performed continuously after the first step, and at 400 ° C. or more, and, the first high rather than the heating temperature, to alpha-Al phase of Cu And a second step of performing heat treatment at a second heating temperature at which the solid solution amount becomes a desired solid solution amount .

According to the present invention, an aluminum alloy die-cast member made of an Al—Si—Cu alloy is heated at a first heating temperature and time at which the volume expansion coefficient is 0.4% or less, and then 400 ° C. or higher. and, it was decided to heat the first high rather than the heating temperature, followed by a second heating temperature solid solution amount of the alpha-Al phase of Cu is desired solute contents.
Therefore, the heat processing method of the aluminum alloy die-casting member which can manufacture the aluminum alloy die-casting member which does not have a blister and has the outstanding intensity | strength can be provided.

FIG. 1 is an Al—Cu binary system phase diagram. FIG. 2 is a photograph showing the appearance of an aluminum alloy die-cast member heat-treated at 500 ° C. for 3 hours. FIG. 3 is a graph showing the heat treatment history in an example of the heat treatment method for the aluminum alloy die cast member of the present invention. FIG. 4 is a graph showing the relationship between the heat treatment time and the volume expansion coefficient. FIG. 5 is a graph showing the relationship between the heat treatment temperature and the volume expansion coefficient. FIG. 6 is a graph showing the relationship between the heat treatment time and the copper concentration ratio. FIG. 7 (A) is a diagram showing a procedure for line analysis of an aluminum alloy die-cast member by an electron beam probe microanalyzer, and FIG. 7 (B) is a graph showing the results of line analysis by an electron beam probe microanalyzer. It is a figure explaining the calculation method of copper concentration ratio. FIG. 8 is a graph showing the strength in each example.

  Hereinafter, an aluminum alloy die casting member heat treatment method and an aluminum alloy die casting member according to an embodiment of the present invention will be described in detail.

[First Embodiment]
First, the heat processing method of the aluminum alloy die-cast member which concerns on 1st Embodiment is demonstrated in detail. The heat treatment method for an aluminum alloy die cast member according to the present embodiment is a heat treatment method for an aluminum alloy die cast member containing Cu, and the heat treatment is performed at a first heating temperature at which the volume expansion coefficient is 0.4% or less. And the second step of performing the heat treatment at the second heating temperature at which a desired solid solution amount is obtained from the solid solution limit line in the Al—Cu binary phase diagram, which is performed after the first step. And including.
In addition, as an aluminum alloy die-casting member containing Cu, conventionally well-known things, such as ADC12, are applicable, for example.

  By passing through such a process, Cu can be sufficiently dissolved in the α-Al phase, and the strength is improved by about 10 to 20% compared to the case where the heat treatment is simply performed at the heating temperature of 460 ° C., An aluminum alloy die casting member having excellent strength can be obtained.

  Here, the “volume expansion coefficient” can be calculated, for example, by measuring the specific gravity before and after the heat treatment by the Archimedes method. However, it is not limited to what was measured and calculated by such a method.

  For example, as can be seen from the Al—Cu binary phase diagram shown in FIG. 1, the amount of solid solution of Cu is determined by the temperature. Therefore, in order to obtain the amount of solid solution of Cu, the solid solution of desired Cu is obtained. It is necessary to heat-treat at a temperature higher than the amount.

Specifically, in an aluminum alloy die-cast member containing 3.0% by mass of Cu, in order to completely dissolve Cu in the α-Al phase, from the Al—Cu binary phase diagram, 460 It is necessary to heat-treat at a temperature of at least ° C.
Further, even at such a temperature, in order to have sufficient time for solid solution diffusion of Cu, it is necessary to perform heat treatment for a long time, for example, heat treatment is preferably performed for 3 hours or more.

  However, in the case of an aluminum alloy die-cast member, if heat treatment is performed at a temperature of 460 ° C. or higher for a long time, blistering (blowing of internal gas) occurs and the quality on appearance deteriorates, so that heat treatment cannot be performed for a long time. For example, FIG. 2 is a photograph showing the appearance of an aluminum alloy die-cast member that has been heat-treated at 500 ° C. for 3 hours. It can be confirmed that blisters are generated in the portion surrounded by the encircling line in FIG.

Therefore, the present inventors have focused on the fact that a certain amount of Cu is dissolved in the α-Al phase even when heat treatment is performed at a low temperature of about 400 ° C. or less. Specifically, the maximum solid solution amount of Cu at 400 ° C. is about 1.2% by mass.
FIG. 3 is a graph showing the heat treatment history in an example of the heat treatment method for the aluminum alloy die cast member of the present invention. As the first step, heat treatment is performed at a low temperature (around 400 ° C.) (the part indicated by symbol a in FIG. 3), and then, as the second step, the solid solution limit line in the Al—Cu binary phase diagram From 400 ° C. or higher, for example, 450 to 500 ° C., at which a desired solid solution amount is obtained, and heat treatment is performed at that heating temperature (part indicated by symbol b in FIG. 3), whereby Cu is α It has been found that it can be sufficiently dissolved in the Al phase.

Furthermore, the present inventors diligently studied the heat treatment time and the heating temperature at which blisters are not generated.
For example, FIG. 4 is a graph showing the relationship between the heat treatment time and the volume expansion coefficient, and FIG. 5 is a graph showing the relationship between the heat treatment temperature and the volume expansion coefficient. 4 and 5, it is found that in the first step, blistering does not occur if the volume expansion coefficient after the heat treatment war of the aluminum alloy die-cast member is 0.4% or less and the heat treatment time. It was. In particular, if the heating temperature is 400 ° C. or less, no blister is generated even if the heat treatment is performed for a long time.

  At present, we believe that the effect is obtained by the following mechanism.

  Heat treatment at a low temperature (around 400 ° C.) can provide diffusion energy that dissolves up to the solid solubility limit of Cu, and further heat treatment at a high temperature in a short time allows the remaining Cu together with Cu having diffusion energy. Can be completely dissolved.

  However, the above mechanism is based on estimation. Therefore, it goes without saying that even if the above-described effect is obtained by a mechanism other than the above-described mechanism, it is included in the scope of the present invention.

  Moreover, in the heat processing method of the aluminum alloy die-cast member of this embodiment, it is preferable to make 2nd heating temperature in a 2nd process higher than 1st heating temperature in a 1st process.

By passing through such a step, Cu dissolved in the α-Al phase in the first step is suppressed from being discharged (precipitated) out of the α-Al phase in the second step, which is excellent. An aluminum alloy die-cast member having high strength can be obtained.
On the other hand, when the second heating temperature in the second step is lower than the first heating temperature in the first step, Cu dissolved in the α-Al phase in the first step becomes α in the second step. -It may be discharged (deposited) out of the Al phase, and the strength may not be improved.

Furthermore, in the heat treatment method for an aluminum alloy die cast member according to the preferred embodiment described above, for example, the heat treatment time in the second step is preferably 1 hour or less.
This is because in the second step, blistering may occur when heat treatment is performed at a high temperature for a long time. In addition, from the viewpoint of sufficiently securing the solid solution diffusion time in the solution treatment in the second stage, the heat treatment time in the second step is preferably 1 minute or longer, and is 15 minutes or longer. Is more preferable, and it is still more preferable that it is 30 minutes or more.

  Moreover, in the heat treatment method of the aluminum alloy die-cast member of the present embodiment, for example, from the viewpoint of sufficiently securing the solid solution diffusion time in the first-stage solution treatment, the heat treatment time in the first step Is preferably 3 hours or longer.

  Furthermore, in the heat treatment method for an aluminum alloy die-cast member of the present embodiment, the second step in which the sum of the volume expansion coefficient in the first step and the volume expansion coefficient in the second step is 0.4% or less. It is preferable to set it as the heat treatment time. Thereby, generation | occurrence | production of a blister can be prevented more reliably.

  FIG. 6 is a graph showing the relationship between the heat treatment time and the Cu concentration ratio described later in detail. In the implementation test example, following the first step of heat-treating the aluminum alloy die-cast member containing copper for 3 hours at 400 ° C. included in the first heating temperature where the volume expansion coefficient is 0.4% or less, A second step of heat treatment at 460 ° C. for each heat treatment time was performed. On the other hand, in the comparative test example, the aluminum alloy die-cast member containing copper was subjected to heat treatment at 460 ° C. not included in the first heating temperature at which the volume expansion coefficient was 0.4% or less. The line segment c in FIG. 6 represents the Cu concentration when the aluminum alloy die-cast member containing copper is heat-treated at 500 ° C. for 3 hours not included in the first heating temperature at which the volume expansion coefficient is 0.4% or less. Indicates the ratio.

  Here, the “Cu concentration ratio” indicates that a large value indicates that the amount of Cu dissolved in the α-Al phase is small, and a small value indicates a large amount of Cu dissolved in the α-Al phase. It is an index indicating that.

  Therefore, it can be seen from FIG. 6 that when the heat treatment method included in the scope of the present invention (execution test example) is performed, the solid solution amount of Cu is significantly increased.

Moreover, Cu concentration ratio can be prescribed | regulated as follows, for example.
FIG. 7A is a diagram showing a procedure for analyzing the aluminum alloy die-cast member at the line segment d by the electron beam probe microanalyzer, and FIG. 7B is a line at the line segment d by the electron beam probe microanalyzer. In the graph which shows the result of an analysis, it is a figure explaining the calculation method of copper concentration ratio. As shown in FIG. 7, paying attention to the α-Al phase in the aluminum alloy die-cast member, the ratio of the count number (2) at the precipitation site around the α-Al phase to the count number (1) in the α-Al phase. ((2) / (1)) can be defined as the Cu concentration ratio.

[Second Embodiment]
Next, the aluminum alloy die casting member according to the second embodiment will be described in detail. The aluminum alloy die-cast member of this embodiment is manufactured by, for example, the heat treatment method for an aluminum alloy die-cast member according to the first embodiment described above.

  By adopting such a configuration, there is no blister, and the strength is improved by about 10 to 20% compared to the case where the heat treatment is simply performed at a heating temperature of 460 ° C.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples.

Example 1
The aluminum alloy die-cast member ( ADC 12) is subjected to a heat treatment for 3 hours at 400 ° C. included in the first heating temperature at which the volume expansion coefficient is 0.4% or less as the first step, followed by the second step. As a process of this example, it heat-processes for 1 hour at 460 degreeC contained in the 2nd heating temperature used as the solid solution amount of 3.0 mass% from the solid solution limit line in an Al-Cu binary system phase diagram, An aluminum alloy die-cast member was obtained.

(Comparative Example 1)
The aluminum alloy die cast member ( ADC 12) was heat-treated at 460 ° C. for 3 hours to obtain an aluminum alloy die cast member of this example.

[Performance evaluation]
(Strength test)
A JIS No. 14B tensile test piece was prepared from the aluminum alloy die cast member of each example by machining, and the tensile strength and proof stress were measured. In addition, about the tensile test piece and the tensile test method, it conformed to JIS-Z-2201 and Z-2241. The obtained result is shown in FIG.

  Specifically, the tensile strength was obtained from the breaking load and the cross-sectional area of the parallel portion of the tensile test piece measured in advance. The yield strength was obtained from a load and a cross-sectional area at a strain of 0.2% from a load-strain diagram using an extensometer.

(Appearance observation)
The external appearance of the aluminum alloy die-cast member of each example was observed visually to check for the occurrence of blisters.

  From FIG. 8, it can be seen that the aluminum alloy die-casting member in Example 1 belonging to the scope of the present invention has improved tensile strength and proof stress compared to the aluminum alloy die-casting member in Comparative Example 1 outside the present invention, It can be seen that it has excellent strength. Moreover, in the aluminum alloy die-cast member in Example 1, generation | occurrence | production of blister was not observed, but in the aluminum alloy die-cast member in Comparative Example 1, generation | occurrence | production of blister was observed.

  As mentioned above, although this invention was demonstrated with some embodiment and an Example, this invention is not limited to these, A various deformation | transformation is possible within the range of the summary of this invention.

Claims (4)

A heat treatment method for an aluminum alloy die-cast member made of an Al-Si-Cu alloy,
A first step of performing heat treatment at a first heating temperature and time at which the volume expansion coefficient is 0.4% or less;
Above is performed continuously after the first step, and at 400 ° C. or more, and, the first high rather than the heating temperature, amount of solid solution to the alpha-Al phase of Cu and desired solute contents heat treatment method of an aluminum alloy die cast members that a second step, characterized in that it comprises a heating treatment at a second heating temperature becomes. In the first step, heat treatment is performed at 200 ° C. to 400 ° C. for 3 hours to 5 hours,
2. The heat treatment method for an aluminum alloy die-cast member according to claim 1, wherein in the second step, heat treatment is performed at 450 ° C. to 500 ° C. for 1 minute to 1 hour.   The heat treatment method for an aluminum alloy die-cast member according to claim 2, wherein the temperature of the heat treatment in the second step is 460 ° C or lower.   The heat treatment method for an aluminum alloy die-cast member according to claim 2 or 3, wherein the heat treatment time in the second step is 30 minutes or more.

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