JP6340170B2 - Aluminum alloy plate and aluminum alloy member - Google Patents

Description

  The present invention relates to an aluminum alloy plate. More specifically, the present invention relates to an Al—Si—Mg based aluminum alloy plate.

  In recent years, due to consideration for the global environment and the like, social demands for weight reduction of vehicles such as automobiles are increasing. In order to respond to such demands, as a material for large body panels (outer panels, inner panels) such as automobile panels, especially hoods, doors, roofs, etc., instead of steel materials such as steel plates, it was excellent in formability and paint bake hardening properties. The application of lighter aluminum alloy materials is increasing.

  As the aluminum alloy material, Al-Mg-Si-based AA to JIS standard 6000 series (hereinafter also simply referred to as 6000 series) aluminum alloy plates are often used.

  This 6000 series (Al-Mg-Si) aluminum alloy sheet is hardened by the paint baking process of the panel after press molding to the panel, and the strength (hardness) is improved, ensuring the necessary strength as a panel. It has excellent paint bake-hardening properties. Hereinafter, this paint bake hardening property is also referred to as bake hard property or BH property.

  Conventionally, various proposals have been made to control Mg—Si clusters for improving the bake hardening characteristics of such 6000 series aluminum alloy plates. With regard to this cluster control, recently, these Mg-Si based clusters are controlled after being measured at an endothermic peak or an exothermic peak of a differential scanning calorimetry (hereinafter also referred to as “DSC”) curve of a 6000 series aluminum alloy plate. Techniques to do this have been proposed.

  For example, in Patent Documents 1 and 2, it is proposed to regulate the amount of these Mg-Si-based clusters, particularly Si / vacancy clusters (GPI), as a factor inhibiting the age-hardening ability at low temperatures. ing. In Patent Document 1, in order to regulate the production amount of GPI that inhibits room temperature aging suppression and low-temperature age-hardening ability, in DSC of T4 material (after solution aging and after natural aging), 150- It defines that there is no endothermic peak in the temperature range of 250 ° C. Moreover, in patent document 1, in order to suppress thru | or control this production | generation of GPI, after performing solution treatment and quenching to room temperature, the low temperature heat processing hold | maintained at 70-150 degreeC for about 0.5 to 50 hours is performed.

  Further, in Patent Document 3, in order to obtain age hardening ability at a low temperature, in a DSC curve after tempering treatment including solution treatment and quenching treatment of excess Si type 6000 series aluminum alloy material, Si / vacancy cluster (GPI ) To control the negative endothermic peak height in the temperature range of 150 to 250 ° C. corresponding to the dissolution of) and the positive exothermic peak height in the temperature range of 250 to 300 ° C. corresponding to the precipitation of Mg / Si clusters (GPII). ing.

In Patent Document 4, to obtain the age hardening ability at low temperature, and in the DSC curve after refining of 6000 series aluminum alloy sheet, the exothermic peak heights _{W 1} in the temperature range of 100 to 200 ° C. 50 W or higher, and The ratio W ₂ / W ₁ between the exothermic peak height W ₂ and the W ₁ in the temperature range of 200 to 300 ° C. is 20.0 or less. Here, the exothermic peak W ₁ corresponds to the precipitation of the GP zone that becomes the nucleation site of the β ″ phase (Mg ₂ Si phase) during the artificial age hardening treatment, and the higher the peak height of W ₁ is, It is assumed that a GP zone that becomes a nucleation site of β ″ at the time of artificial age hardening is formed and secured in advance on the plate after the tempering treatment. On the other hand, the exothermic peak W ₂ corresponds to the precipitation peak of the β ″ phase itself, and the exothermic peak W _{2 has} a higher exothermic peak W ₂ in order to ensure the formability by reducing the yield strength of the press-formed plate in advance. The size is supposed to be small.

Japanese Patent Laid-Open No. 10-219382 JP 2000-273567 A JP 2003-27170 A JP 2005-139537 A

  However, even with the above-described prior art, an Al—Si—Mg-based aluminum alloy plate that is easy to age harden at room temperature and has various conditions such as room temperature aging time, has a heating temperature of 150 ° C. or 135 ° C. There is a fact that it is difficult to stably achieve high strength (high hardness) by low-temperature paint baking and curing treatment.

  The present invention has been made in view of the above circumstances, and mainly provides an Al—Si—Mg-based aluminum alloy plate that can obtain a stable high strength even by low-temperature paint baking and hardening treatment. Objective.

That is, the present invention is an aluminum alloy plate for low-temperature paint bake-hardening treatment in which a β ″ phase is precipitated after low-temperature paint bake-hardening treatment in which the heating temperature is in the range of 135 to 170 ° C., and Mg: 0.2- 2.0 wt%, Si: 0.3 to 2.0 wt%, Fe: 0.5 wt% or less, Li: 0.005 to 0.1 include mass%, the balance being Al and unavoidable impurities An aluminum alloy plate and an aluminum alloy member after a low-temperature paint bake hardening process in which the heating temperature is in the range of 135 to 170 ° C., Mg: 0.2 to 2.0 mass%, Si: 0.3 to 2. Aluminum alloy member containing 0% by mass, Fe: 0.5% by mass or less, Li: 0.005 to 0.1% by mass, the balance being made of Al and inevitable impurities, and β ″ phase being precipitated I will provide a.

  According to the present invention, it is possible to obtain an Al—Si—Mg-based aluminum alloy plate that can stably obtain high strength even by low-temperature paint bake hardening treatment.

Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below.
Further, the “aluminum alloy plate” in the present invention refers to a plate (rolled plate) after cold rolling and after tempering treatment.

Chemical composition of aluminum alloy sheet:
First, the chemical component composition of the 6000 series aluminum alloy plate according to the embodiment of the present invention will be described.

The target 6000 series aluminum alloy plate is age-hardened by heating at a relatively low temperature artificial aging treatment of, for example, 135 ° C. to 170 ° C. after being molded into an automobile panel, for example, paint baking treatment, and required strength It is required to have excellent age-hardening ability (BH property) that can ensure (hardness).
In addition, various properties such as excellent formability and weldability, and corrosion resistance are also required for the above-described automobile outer plate.

  In order to satisfy such required characteristics, in the aluminum alloy plate according to the present embodiment, Mg: 0.2 to 2.0 mass%, Si: 0.3 to 2.0 mass%, Fe: 0.5 mass% % And Li: 0.005 to 0.1 mass%, respectively, and the balance is defined as consisting of Al and inevitable impurities.

  Other than these Mg, Si, Fe, and Li, other elements such as Mn, Cu, Cr, Ti, and Zn all have an O.O. The content (allowable amount) is 02% by mass or less.

  The content range and significance or allowable amount of each element will be described below.

[Si: 0.3 to 2.0% by mass]
Si, together with Mg, in the aluminum alloy plate of the present embodiment, during the artificial aging treatment at a low temperature of, for example, 135 ° C. to 170 ° C., such as paint baking treatment, the amount of precipitation of β ″ phase, which is an aging precipitate that works on BH properties In addition, it is an essential element for enhancing age-hardening ability, and also has the effect of improving solid solution strengthening and total elongation that affects press formability.

However, when the Si content is less than 0.3% by mass, the absolute amount of Si is insufficient, so that the precipitation amount of the β ″ phase is insufficient, and the BH property may be significantly lowered. It becomes difficult to combine mechanical properties such as total elongation.
On the other hand, when the Si content exceeds 2.0% by mass, coarse crystallized products and precipitates are formed, and bending workability, total elongation, and the like may be significantly reduced. Furthermore, weldability may be significantly impaired.
Therefore, in the aluminum alloy plate of the present embodiment, the Si content is set to 0.3 to 2.0 mass%, preferably 0.5 to 1.2 mass%.

[Mg: 0.2 to 2.0% by mass]
Mg is an essential element for enhancing age-hardening ability by precipitation of β ″ phase, which is an aging precipitate effective for BH properties, at the time of artificial aging treatment at low temperatures such as paint baking treatment together with Si. There is also an effect of improving solid solution strengthening and total elongation that affects press formability.

However, when the Mg content is less than 0.2% by mass, the absolute amount of Mg is insufficient, so that the precipitation amount of the β ″ phase is insufficient, and the BH property may be significantly lowered. It becomes difficult to combine mechanical properties such as total elongation.
On the other hand, when the Mg content exceeds 2.0% by mass, coarse crystallized substances and precipitates are formed, and there is a possibility that bending workability, total elongation, and the like are remarkably reduced. Furthermore, weldability may be significantly impaired.
Therefore, in the aluminum alloy plate of this embodiment, the Mg content is 0.2 to 2.0 mass%, preferably 0.3 to 1.0 mass%.

[Fe: 0.5% by mass or less]
From the viewpoint of recycling aluminum alloy sheets, not only high-purity aluminum bullion but also aluminum alloy scrap material, low-purity aluminum bullion, etc. are used as melting raw materials. ) Will inevitably increase. However, since Fe forms an intermetallic compound with Al, as long as the Fe content is up to 0.5% by mass, it does not adversely affect the effects of the Li content in the aluminum alloy plate of this embodiment. .
Therefore, in the aluminum alloy plate of the present embodiment, the Fe content is 0.5 mass% or less, preferably 0.3 mass% or less.

[Li: 0.005 to 0.1% by mass]
Li promotes the precipitation of the β ″ phase effective for the BH property during the artificial aging treatment at a low temperature such as the paint baking treatment, and increases the precipitation amount of the β ″ phase. In this respect, Li is an essential element for enhancing age hardening ability.

When the Li content is less than 0.005% by mass, the absolute amount of Li is insufficient, so that the precipitation amount of the β ″ phase is insufficient, and the BH property may be significantly lowered.
On the other hand, Li is difficult to be contained in the ingot at the time of melting and casting, and cannot be contained in a large amount. On the other hand, if the Li content exceeds 0.1% by mass, the moldability, total elongation, and the like may be significantly reduced.
Therefore, in the aluminum alloy plate of the present embodiment, the Li content is set to 0.005 to 0.1% by mass, preferably 0.02 to 0.1% by mass.

  In the field of 6000 series aluminum alloy plates, Japanese Patent Application Laid-Open No. 11-71623 discloses finely crystallized products produced during casting for the purpose of improving the press formability, corrosion resistance, and strength after paint baking for automobile body panels. It is disclosed that at least one of the elements Na, Sr, Sb, Ca, Te, Ba, Li, K, Bi, P, As, and Se is added for dispersion or spheroidization. As described above, in this patent document, it is described that Li can be used as an additive element for finely dispersing or spheroidizing the crystallized product generated at the time of casting, but it is not specialized in Li. Absent.

  Like the aluminum alloy plate of the present embodiment, it promotes the precipitation of the β ″ phase, which is an aging precipitate that is effective for BH at the time of coating baking at low temperature, which is a unique effect of only Li among the aforementioned elements. The effect was neither recognized nor suggested in the prior art.

  In addition, in the above-mentioned Japanese Patent Application Laid-Open No. 11-71623, as described above, Li can be added, but also in the examples, the manufacturing method of the plate is only described as being manufactured by annealing after cold rolling. is there. That is, this patent document does not describe specific conditions such as whether the annealing (tempering treatment) is a solution treatment, a quenching treatment, or a simple annealing, and temperature conditions thereof. Therefore, in this patent document, it is completely unknown whether or not a β ″ phase precipitate exists as defined by the aluminum alloy plate according to the present embodiment. There is a higher probability of not.

[Balance: Al and inevitable impurities]
Components other than the above-described components of Mg, Si, Fe, and Li, that is, the balance, are Al and inevitable impurities. In particular, in the aluminum alloy plate of the present embodiment, inevitable impurities are restricted to a content (allowable amount) of 0.02% by mass or less in order to exert the effect of the Li content in the aluminum alloy plate. Examples of inevitable impurities include Mn, Cu, Cr, Ti, and Zn.

Production method:
Next, the manufacturing method of the aluminum alloy plate of this embodiment is demonstrated.
The aluminum alloy plate of this embodiment is subjected to homogenization heat treatment after casting the above-mentioned aluminum alloy ingot having the above-mentioned 6000 series composition, and is subjected to hot rolling and cold rolling to a predetermined plate thickness, and further is solution-quenched and the like The tempering treatment is applied.

(Dissolution, casting cooling rate)
First, in the melting and casting process, an ordinary molten casting method such as a continuous casting method and a semi-continuous casting method (DC casting method) is appropriately selected for the molten aluminum alloy adjusted to be dissolved within the above-mentioned 6000 series component composition range. Cast.

(Homogenization heat treatment)
Next, the cast aluminum alloy ingot is subjected to a homogenization heat treatment prior to hot rolling. This homogenization heat treatment (soaking) is performed for the purpose of homogenizing the structure, that is, eliminating segregation in the crystal grains in the ingot structure. Therefore, the homogenization heat treatment temperature is appropriately selected from the range of 500 ° C. or higher and less than the melting point of the aluminum alloy plate, and the homogenization time of 4 hours or more.

(Hot rolling)
The hot rolling after the homogenization heat treatment is preferably performed at a start temperature of 400 ° C. to a solidus temperature. Although annealing (roughening) of the hot-rolled sheet before cold rolling is not necessarily required, it may be performed to further improve the properties such as formability.

(Cold rolling)
In cold rolling, the hot rolled sheet is rolled into a cold rolled sheet having a desired final sheet thickness. For the same purpose as the roughening, intermediate annealing may be performed between the cold rolling passes.

(Solution and quenching)
A solution-quenching treatment is performed as a tempering treatment on the cold rolled sheet. In order to obtain a sufficient solid solution amount of each element, the solution treatment temperature is preferably set to 520 ° C. or higher. The holding time should be as long as possible. Moreover, in order to suppress the formation of coarse grain boundary compounds that lower the moldability, the cooling rate during quenching is desirably as fast as possible, and water cooling is preferable.

(Reheating treatment)
If necessary, the plate obtained after quenching and cooling to room temperature is reheated (preliminary aging treatment). This reheating treatment is preferably performed in a temperature range of 70 to 150 ° C. for 1 hour or longer in a batch furnace.

  In the aluminum alloy plate of this embodiment described above, 6000 series aluminum alloy contains Li in a specific range. This provides a 6000 series aluminum alloy plate that stably increases the strength (hardness) after coating baking even when the heating temperature is a coating baking hardening process at a low temperature such as 135 ° C. to 170 ° C. be able to. For this reason, the aluminum alloy plate of this embodiment is applicable to the members of transport machines, such as a motor vehicle.

  Hereinafter, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention.

  In the examples and comparative examples described below, 6000 series aluminum alloy plates were separately prepared under the tempering (reheating treatment) conditions after solution treatment and quenching treatment.

As shown in Table 1, 6000 series aluminum alloy cold-rolled sheets of Examples 1 and 2 having the same alloy composition and Comparative Examples 1 and 2 having the same alloy composition were produced, respectively, and after solution treatment and quenching treatment. The tempering process was divided into two types, Type A and Type B.
The tempering process type A was an aluminum alloy plate that was kept at room temperature for 30 minutes after solution treatment and quenching treatment.
The tempering process type B was an aluminum alloy plate kept at room temperature for 30 minutes after a pre-aging treatment at 100 ° C. for 5 hours after the solution treatment and quenching treatment.

The specific production conditions for the aluminum alloy cold-rolled sheet are as follows.
Ingots having respective compositions shown in Table 1 were commonly melted by DC casting to form ingots. At this time, Examples 1 and 2 had the same composition containing Li, and Comparative Examples 1 and 2 had the same composition not containing Li. Subsequently, the ingot was subjected to a soaking treatment at 540 ° C. for 4 hours in common with each example, and then hot rolling was started at a hot rolling start temperature of 540 ° C. to obtain a hot rolled plate having a thickness of 2.5 mm. . In common with each example, this hot-rolled sheet was cold-rolled without any rough firing and without intermediate annealing in the middle of the cold-rolling pass to obtain a cold-rolled sheet having a thickness of 1.0 mm.

  Furthermore, each cold-rolled sheet was subjected to a solution hardening treatment in which each of the cold-rolled plates was subjected to a solution treatment in a glass stone furnace at 550 ° C. for 30 minutes and then immediately cooled to room temperature. Thereafter, the two types of tempering, Type A and B, were performed.

  A test plate (blank) was arbitrarily cut out from each tempered aluminum alloy plate, and the structure and characteristics of each test plate were measured and evaluated as follows. These results are also shown in Table 1.

(Paint bake-hardening properties)
In order to investigate the strength after the artificial aging treatment equivalent to the paint baking of the test plate, each example was held at different temperatures of 135 ° C., 150 ° C., and 170 ° C. for 20 minutes in common.

(Vickers hardness)
Vickers hardness was measured with a Vickers hardness tester (manufactured by Matsuzawa Co., Ltd.) by applying a load of 0.5 kg, measuring seven arbitrary locations on the surface of the test plate, and excluding the maximum and minimum values. Five point values were averaged. This measurement was performed after artificial aging treatment at 135 ° C, 150 ° C, and 170 ° C. The results are shown in Table 1.

  As shown in Table 1, Examples 1 and 2 were within the scope of the present invention, including Li as a composition. As a result, in the aluminum alloy plates of Examples 1 and 2, the Vickers hardness after the artificial aging treatment at temperatures of 135 ° C., 150 ° C., and 170 ° C. is higher than that of the comparative example of the same tempering process type. It was a thing.

  On the other hand, the aluminum alloy plates of Comparative Examples 1 and 2 are manufactured under the same conditions as in the Examples including the tempering, but do not contain Li. As a result, in the aluminum alloy plates of Comparative Examples 1 and 2, the Vickers hardness after the artificial aging treatment at each temperature of 135 ° C., 150 ° C., and 170 ° C. is inferior to the examples of the same tempering process type. It was.

  From the results of the above examples, it is confirmed that there is a need to satisfy Li and the structure defined in the present invention for the strength improvement after artificial aging treatment corresponding to paint baking under low temperature conditions.

Claims (2)

An aluminum alloy plate for low-temperature paint bake-hardening treatment in which a β ″ phase is precipitated after low-temperature paint bake-hardening treatment in which the heating temperature is in the range of 135 to 170 ° C.,
Mg: 0.2-2.0 mass%,
Si: 0.3 to 2.0 mass%,
Fe: 0.5% by mass or less,
Li: 0.005 to 0.1% by mass,
Aluminum alloy plate and the balance of Al and unavoidable impurities. It is an aluminum alloy member after a low temperature paint bake hardening process in which the heating temperature is in the range of 135 to 170 ° C,
Mg: 0.2-2.0 mass%,
Si: 0.3 to 2.0 mass%,
Fe: 0.5% by mass or less,
Li: 0.005 to 0.1% by mass,
An aluminum alloy member in which the balance is made of Al and inevitable impurities, and a β ″ phase is precipitated.