JPH05261405A - Hot rolling method for cu-added high-mg aluminum alloy - Google Patents

Abstract

PURPOSE:To enable hot rolling of a Cu-added high-Mg aluminum alloy which has high yield strength after baking coating and is the major aluminum alloy for recent automobile plates without requiring a long-eriod homogenization treatment and without generating cracks. CONSTITUTION:This method consists in hot rolling the aluminum alloy contg., by weight %, 4 to 8% Mg and Cu at such a ratio at which Mg(%)/8+5Cu(%)/6g1 is satisfied at such a temp. X deg.C at which 1000<=(X+273)XLog(100Y)<=2500 is satisfied and at a strain speed Y/s after heating for <=4 hours at <=400 deg.C. The alloy contains, in some cases, Fe and Se respectively at 0.5% max., Mn at 0.7% max., Cr, Zn, Ti, Band Zr respectively at 0.3% max. and Be at 0.1% max. As a result, the Cu-added high-Mg aluminum alloy having high strength and large elongation is hot rolled without executing the long-period homogenization treatment and without generating cracks.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling method for Cu-added high Mg aluminum alloy.

[0002]

2. Description of the Related Art In recent years, the position of automobiles as a convenient and comfortable means of transportation in the people's lives has been increasing year by year. To prevent environmental damage and regional warming, fuel consumption is reduced and fossil fuel consumption is suppressed. It is becoming more important than ever before. For this reason, improvement in engine performance and weight reduction of vehicle bodies are required, and application of aluminum alloys is being expanded. Among them, the inner and outer panels are required to have strength and rigidity equivalent to those of thin steel sheets that have been used so far, and they may have some formability as long as they are formed by pressing. Required. Such alloys that are compatible with formability and strength include solid solution hardening type 5000 alloys containing 4% or more of Mg or 0.5 to 2% S.
There is an age-hardening type 6000 series alloy in which i and Mg are added in combination and a fine compound is precipitated during baking coating. Among them, a 5000 series alloy having a large elongation as described in JP-A-62-27544 has been recently used. Is becoming the mainstream of aluminum alloys for automobiles.

The production of an aluminum alloy sheet comprises a number of steps, but the steps of casting the molten metal into a slab after adjusting the components and destroying the solidified structure present in the slab to obtain the required sheet thickness are continued. The hot rolling process is extremely important. However, it is difficult to obtain the initial rolling reduction at low temperature because the aluminum alloy containing a large amount of Mg is significantly solid-solution hardened and has a large deformation resistance. There is a problem that cracks in the mouth are likely to occur. In order to avoid this, it is necessary to remove the non-equilibrium low melting point phase generated due to solidification segregation, and it takes 4 to 48 hours at a high temperature of 426 ° C. or higher as proposed in JP-B-53-6086. It has been common practice to carry out a homogenizing treatment for a long time and then hot-roll at a rolling reduction of up to 95% at 329 to 404 ° C.

[0004]

However, the homogenizing treatment for a long time prior to hot rolling has a large amount of energy and causes a cost increase. In addition, in order to obtain dent resistance, it is required that the yield strength be large after press-molding and baking coating on the outer plate. For that purpose, in addition to Mg, Cu of about 0.05 to 0.4% is required. Even if the alloy added with is subjected to homogenizing treatment and then hot rolling at a low temperature, cracks may occur during hot rolling. The present invention solves such a problem and provides a method of hot rolling a Cu-added high Mg aluminum alloy without homogenizing for a long time.

[0005]

In order to solve the above problems, it is important to regulate the amount of Cu according to the amount of Mg added and to control the strain rate together with the rolling temperature during hot rolling. Focusing attention, the present invention has been made.
That is, the present invention is directed to 4-8% by weight of Mg and Mg.
(%) / 8 + 5 Cu (%) / 6 ≦ 4, an aluminum alloy containing Cu in an amount satisfying 4 ≦ 4 ° C.
1000 ≤ (X + 273) x Lo after heating for no more than time
The gist is a method of hot rolling at a strain rate of Y / s at a temperature of X ° C. that satisfies the expression g (100Y) ≦ 2500.

Next, the reason why these alloy components are limited will be described. Mg is an alloying element that increases strength without impairing formability, which is represented by elongation, when added in a certain amount or more, and in order to exert its effect, 4
% Addition is required. If added in excess of 8%, cracking may occur even if hot rolling is performed under the conditions of the present invention, and it is necessary to avoid it. Cu is an element that finely precipitates during baking coating after press molding to increase the yield strength, and is added in an amount that satisfies Mg (%) / 8 + 5Cu (%) / 6 ≦ 1. Mg (%) / 8 + 5Cu
If the value of (%) / 6 exceeds 1, an intermetallic compound that dissolves at a low temperature at the grain boundary is generated, and cracks are likely to occur even if hot rolling is performed under the conditions of the present invention, so it must be avoided. .. In addition to the above, the aluminum alloy of the present invention has a maximum grain size of 0.5% for Fe and Si and a maximum Mn content of 0 for the purpose of refining crystal grains, preventing oxidation, and inevitably as inevitable impurities. 0.7%, Cr, Zn,
Each element of Ti, B, Zr is 0.3% at maximum, B
e may be contained at a maximum of 0.1%, and even in that case, the hot rolling property does not extremely deteriorate.

Next, the reasons for limiting the hot rolling conditions of the present invention will be described. In the present invention, prior to hot rolling, the ingot of the above alloy has a temperature range of 400 ° C. or higher and a solid phase temperature of the alloy of 4 °
Heated for less than an hour. This reduces solidification segregation of the ingot,
It is also intended to re-dissolve an Al-Mg-Cu intermetallic compound. That is, Mg and Cu segregate at the grain boundaries during solidification, and are then liquefied at a low temperature when gradually cooled.
The Cu-based intermetallic compound is formed to remarkably reduce the drawing limit during hot working, but the purpose is to avoid this coarse precipitate. If the heating temperature is lower than 400 ° C., the diffusion of Mg and Cu will be insufficient, causing precipitation and cracking during rolling. Further, heating for more than 4 hours leads to an increase in energy cost, and if heating is performed for an extremely long time, coarse crystal grains are added even when Mn, Cr, etc. are added with the intention of refining the crystal. Should be avoided because it may grow and deteriorate the hot rolling property.

The hot rolling of the present invention is 1000 ≦ (X + 27
3) × Log (100Y) ≦ 2500 is performed at a strain rate of Y / s at a temperature of X ° C. that satisfies the equation. If this condition is satisfied, it is possible to obtain the required plate thickness without causing significant cracking on the way even if the homogenization treatment is not performed for a long time at a high temperature. High temperature, (X + 273) × Lo
If the value of g (100Y) is larger than 2500, Al-M
The g-Cu-based intermetallic compound melts during hot rolling and cracks occur. In addition, the strain rate is large, (X + 273) × L
When the value of og (100Y) is more than 2500, the temperature in the hot-rolled sheet becomes non-uniform due to the heat generated during processing, and a difference in deformability is likely to occur. It may cause cracks. On the other hand, the temperature is low, and the value of (X + 273) × Log (100Y) is 1
If it is less than 00, the alloy is significantly solid-solution hardened, and it is uneconomical to use a rolling mill having a large capacity to finish the required plate thickness, and in some cases, a remarkable work structure may be left. So you have to avoid it. Also (X
In hot rolling at a strain rate such that the value of +273) × Log (100Y) is smaller than 1000, it takes an extremely long time to reach the required sheet thickness, which is not practical. The aluminum alloy hot-rolled under the conditions of the present invention is used as it is, or after being subjected to steps such as cold rolling and recrystallization annealing, it becomes a coil or sheet to be press-formed for automobile plates.

[0009]

EXAMPLE An aluminum alloy having the plate thickness of 500 mm and having the components shown in Table 1 was heated under the conditions shown in Table 2 and then hot-rolled to a finished thickness of 5 mm at the temperature and strain rate shown in Table 2 to obtain a result. The shapes of the finished products are summarized in Table 2 "Cracks".
In the same column, ◯ means that it was able to be rolled to a thickness of 5 mm without cracks, and △ means that even if some care is taken, minute cracks that do not pose a problem have occurred, but hot rolling to a thickness of 5 mm What was possible was that x indicates that a significant crack was generated during hot rolling to such an extent that rolling could not be continued. If hot rolling is performed under the conditions of the present invention, Examples 2, 6, and 2 in Table 2 are performed.
There is no problem as in Examples 11 and 12, and Examples 5 and 15
As described above, the Cu-added high-Mg alloy can be rolled in a relatively good state. Further, in the case of an alloy containing a small amount of Cu or Mg, hot rolling is easy even if the condition of the present invention is not satisfied as in Example 1, but the condition of the present invention is deviated when the amount of Cu or Mg added is large. It is difficult to perform hot rolling as in Examples 3, 4, 7, 10 and 14, and even if it is possible, productivity is remarkably poor due to the low strain rate as in Example 8, or in Example 9 As described above, heating before hot rolling is long and there is a problem in energy cost. Further, when the amount of Cu or Mg added as an alloying element is larger than that specified in the present invention, hot rolling can be industrially satisfied even under the conditions of the present invention as in Examples 13 and 16. It is difficult.

[0010]

[Table 1]

[0011]

[Table 2]

[0012]

As is apparent from the above examples, according to the present invention, a Cu-added high-Mg aluminum alloy having high strength and relatively good formability is cracked without being subjected to a homogenizing treatment for a long time. It is possible to carry out hot rolling without generation of heat, which brings about a very remarkable industrial effect.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Koji Sakuma 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Co., Ltd.Technology Development Division (72) Inventor Mamoru Matsuo 1351 Uenodai, Fukaya, Saitama Sky Aluminum Co., Ltd. Inside the Technical Research Laboratory (72) Inventor Toshio Komatsubara 1351 Uenodai, Fukaya, Saitama Sky Alminium Co., Ltd. Technical Research Center

Claims (1)

[Claims] 1. 4-8% by weight of Mg and Mg
(%) / 8 + 5 Cu (%) / 6 ≦ 4, an aluminum alloy containing Cu in an amount satisfying 4 ≦ 4 ° C.
1000 ≤ (X + 273) x Lo after heating for no more than time
A hot rolling method for Cu-added high Mg aluminum alloy, which comprises hot rolling at a strain rate of Y / s at a temperature of X ° C. that satisfies the expression g (100Y) ≦ 2500.