CN100413986C - Aluminum alloy plate having excellent compression formability and continuous resistance spot weldability and production method thereof - Google Patents

Abstract

The invention provides the aluminum alloy plate which has excellent in press formability and continuous resistance spot weldability and the producing method thereof. An aluminum alloy plate which has a chemical composition, in mass %: Mg: 0.3 to 1.0 %, Si: 0.3 to 1.2 %, Fe: 0.10 to 1.0 %, Mn: 0.05 to 0.5 %, provided that Fe + Mn >= 0.2 %, and the balance: Al and inevitable impurities, has an average re-crystallization grain diameter of 25 mum or less, and contains an intermetallic compound having a diameter of a corresponding circle of 1 to 6 mum in an amount of 5000 pieces/mm<2> or more; the aluminum alloy plate further comprising 0.5 to 1.0 % of Cu, 0.1 to 0.4 % of Zr, 0.05 % or less of Ti or 0.05 % or less of Ti and 0.01 % or less of B; and a method for producing the aluminum alloy plate which comprises pouring a molten alloy having the above composition in the inside of facing rotary belt casting molds being forcedly cooled, solidifying at a cooling rate at the time of solidification of 40 to 90 DEG C/sec to form a slab having a thickness of 5 to 10 mm, drawing the slab from the side opposite to that for pouring, rolling the slab directly or after winding into a coil form, thereby subjecting the alloy to a solution heat treatment.

Description

Aluminum alloy plate having excellent compression formability and continuous resistance spot weldability and production method thereof

technical field

The present invention relates to an aluminum alloy sheet excellent in press formability and continuous resistance spot weldability, which is used as a structural material and assembled by resistance spot welding before or after molding to form outer panels of products such as home appliances or automobiles.

Background technique

Structural materials and outer panels of products such as household appliances and automobiles are first molded and then resistance spot welded to assemble the product.

After compression molding, Al-Mg-Si type alloy sheet (JIS6000) exhibits quite excellent surface quality, so it is used as various types of panels and structural materials, but due to the diversity of product shapes, it is required to have good compression molding sex.

Additionally, there is a need to increase continuous resistance spot welding capabilities to reduce the time during which electrodes are replaced in resistance spot welding.

Japanese Patent Application First Publication No. S62-207851 describes a method for producing rolled sheet, such as body sheet with good formability, comprising the steps of: preparing a or more molten aluminum alloys selected from the group consisting of 1.5% or less copper, 2.5% or less zinc, 0.3% or less chromium, 0.6% or less manganese and 0.3% or less zinc, remaining Partly composed of aluminum and unavoidable impurities; continuous casting of the melt into slabs of 3-15 mm thickness; cold rolling followed by solution heat treatment and quenching.

Furthermore, Japanese Patent Application First Publication No. 2001-262264 describes an Al-Mg-Si type aluminum alloy sheet having good bendability for use as an automobile panel. For example, the application documents disclose that the Al-Mg-Si type aluminum alloy plate has excellent toughness and bendability, mainly including 0.1-2.0% of Mg, 0.1-2.0% of Si and 0.1-1.5% of Fe, the remainder consisting of aluminum, where the iron and silicon containing compounds have a maximum size of 5 microns or less and an average particle size of 15 microns or less. In addition, it also discloses an Al-Mg-Si type aluminum alloy plate with excellent toughness and bendability, mainly including 0.1-2.0% of Mg, 0.1-2.0% of Si, 0.1-1.5% of Fe and 2.0% Fe or less, the remainder consisting of aluminum, where the iron, silicon and copper containing compounds have a maximum particle size of 5 microns or less and an average particle size of 30 microns or less. In addition, the application document also discloses the Al-Mg-Si type aluminum alloy plate having excellent toughness and bendability as described above, further comprising at least one component selected from 1.0% or less manganese, 0.3% or Less zinc, 0.3% or less vanadium, and 0.03% or less titanium.

Japanese Patent Application First Publication No. S62-207851 describes a casting process technique with a cooling rate of at least 100°C/sec, the size of the crystallized intermetallic compounds in the casting is small, and the result is the amount of relatively large compounds that affect the recrystallized grain size Insufficient, such that the particle size after solution heat treatment is large, so the moldability is reduced, and the number of continuous resistance spot welding is reduced.

Japanese Patent Application First Publication No. 2001-262264 discloses a technique using a continuous casting process with a minimum cooling rate of 10°C/sec for casting, but in the examples, a maximum cooling rate of 30°C/sec was used, since the cooling rate is slow , the size of intermetallic compounds crystallized in casting is large, and as a result, the number of relatively large compounds that affect the recrystallized grain size is insufficient, so that the grain size after solution heat treatment is large, reducing the moldability and the number of continuous resistance spot welding.

Contents of the invention

The object of the present invention is to provide an aluminum alloy plate having excellent compression formability and continuous resistance spot weldability, and a production process thereof.

The present inventors achieved the present invention based on the discovery that by selecting an optimal range of cooling rates when casting a melt, the present invention is achieved within an appropriate composition range. The size and amount of crystalline intermetallic compounds can be optimized such that after solution heat treatment aluminum alloy sheets with excellent moldability and continuous resistance spot weldability are obtained.

Therefore, the present invention provides an aluminum alloy plate with excellent moldability and continuous resistance spot weldability, comprising 0.3-1.0% magnesium, 0.3-1.2% silicon, 0.10-1.0% iron and 0.05 -0.5% manganese; where iron + manganese ≥ 0.2%; the remainder consists of aluminum and unavoidable impurities, where the mean value of recrystallized grain size is 25 microns or less, at least 5000 grains/mm ² equivalent circumference diameter 1 -6 μm intermetallic particles.

Due to the refinement of the recrystallized particle size and the majority of the optimum size compound, the present invention has advantages in moldability and continuous resistance spot weldability.

The strength can be further improved by making the above composition contain 0.5-1.0% copper.

By making the above composition contain 0.1-0.4% zirconium, the recrystallized grain size can be made finer and the strength can be further improved.

Casting cracks during casting can be avoided by making the above composition contain 0.05% or less titanium, or 0.05% or less titanium and 0.01% or less boron.

A second aspect of the present invention is a method of producing an aluminum alloy plate having excellent compression formability and continuous resistance spot weldability, comprising casting a melt composed of the above into a counter-rotating forced-cooled belt casting machine, casting The cooling rate of the melt is 40-90° C./sec to form a thick plate of 5-10 mm, and the thick plate is stretched from the opposite side of the melt casting; directly rolled or coiled after winding, and subjected to solution heat treatment.

Most of the optimal particle size compounds can crystallize, and the recrystallized particle size can be refined by casting the alloy at the optimal cooling rate, so that the aluminum alloy plate has excellent moldability and continuous spot weldability.

BEST MODE FOR CARRYING OUT THE INVENTION

Thereafter, the optimum content of each component in the aluminum alloy sheet of the present invention will be described, and then the reasons for the upper and lower limits will be explained. In this specification, unless otherwise specified, all contents represent mass contents.

[Mg: 0.3-1.0%]

[Si: 0.3-1.2%]

Magnesium and silicon are added to increase strength and provide moldability. When the concentration is lower than the lower limit, the effect is not significant, and when the content is higher than the upper limit, the moldability deteriorates.

[Fe: 0.10-1.0%]

[Mn: 0.05-0.5%]

[Fe+Mn≥0.2%]

Adding iron and manganese, and keeping Fe+Mn≥0.2%, can crystallize a large number of compounds with specific sizes, increase the number of recrystallizations, and make the size of recrystallizations smaller. When their concentrations are less than their respective lower limits, the effects are not significant, and when their concentrations exceed the upper limits, large crystals are caused to occur, so that surface stains such as streaks in cold rolling and moldability deteriorate. Except when it coexists with iron, manganese does not crystallize into intermetallic compounds of ideal size and quantity. The total content of iron and manganese is more suitable, such as Fe+Mn≥0.3%.

[Cu: 0.5-1.0%]

Addition of copper further improves strength and moldability. When the concentration of copper is less than the lower limit, its influence is small. When the content is higher than the upper limit, corrosion resistance decreases.

[Zr: 0.1-0.4%]

Zinc promotes the crystallization of the intermetallic compound Al ₃ Zr, further including many crystals of specific size compounds to increase the number of recrystallized nuclei, thus making the recrystallized particles smaller, thereby increasing the moldability. When the concentration is lower than the lower limit, there is no effect, and when the amount exceeds the upper limit, a larger compound is formed and windability decreases.

[Ti: 0.05% or less; or Ti: 0.05% or less and boron: 0.01% or less]

Rapid cooling during pouring of the melt can cause pouring cracks, adding Ti or Ti and boron can prevent these cracks. Ti 0.05% or less can be added alone, or 0.01% or less boron can be added to obtain a compound with Ti, which has a synergistic effect. The effect is very pronounced when the lower limit of Ti is at least 0.002% and the lower limit of boron is at least 0.0005%.

Unavoidable impurities can come from base aluminum, swarf and ferrous fixtures or similar, typically these elements include chromium, nickel, zinc, gallium and vanadium. Chromium is added to prevent stress corrosion of aluminum-magnesium alloys, it can be easily introduced from chips, and in order to maintain formability, less than 0.3% is allowed in the present invention.

[Average recrystallized particle size 25 microns or less]

If the recrystallized particles of the plate after solution heat treatment are small, it can be formed without destroying it even if the pressure design is set high and the tensile height is set high. If the particle size exceeds the upper limit, there is no effect and the surface quality after pressing is not good. The recrystallized particle size is preferably 20 microns or less, 15 microns or less.

[5000/mm ² intermetallic compound, the equivalent diameter of the circle is 1-6 microns]

Intermetallic compounds with a circumference-equivalent diameter of 1-6 microns are sizes that promote fault integration and agglomeration during cold pressing, affecting the refinement of recrystallized grains, so that if the grain size and number are less than the lower limit, the fault aggregation rate is low, and if the number is less than 5000 grains/mm ² , no fine recrystallized grains of appropriate size could be obtained. In addition, if the size exceeds the upper limit, larger compounds can cause streaks or cracks in cold rolling, thereby reducing cold rolling properties. In addition, with the above-mentioned compound state, corrosion can be prevented due to the reaction between the copper electrode and aluminum when continuous resistance spot welding is performed, thereby reducing the number of electrode replacements and improving productivity. The number of compounds is preferably at least 6000 particles/mm ² .

A more suitable process for producing aluminum alloy plates according to the present invention will be described below.

By adjusting the composition, degassing, precipitation, fine-tuning the composition as needed, adding titanium or titanium and boron to prepare the melt as a parent alloy and pouring. When pouring, the melt is poured into the oppositely placed rotating belt for forced cooling, the cooling rate is 40-90°C/sec to form a 5-10mm thick plate, and then the thick plate is stretched from the opposite side of the melt pouring end, and rolled directly It is or is wound into rolls afterwards.

The continuous casting process includes a twin-coil casting process, where the melt is poured between opposing rotating rolls that are forced to cool, the melt is rapidly cooled on the belt surface, and the sheet is continuously stretched from opposite sides.

During casting, the cooling rate of the twin-roll casting process is at least 300°C/sec, which is relatively high, and although the size of the compound in the thick plate produced is small, the plate of the present invention cannot be obtained. On the other hand, the twin-strip casting process involves rapid cooling of the melt on the strip surface, but the cooling rate is not as high as that of the twin-roll casting process.

In the present invention, the pouring conditions of the double-belt pouring process are adjusted so that the melt cooling rate is 40-90° C./sec (at the 1/4 thickness of the thick plate, so as to form more than 5000 particles/mm in the ^final plate. Circumference Intermetallic compounds with an equivalent diameter of 1-6μm. If the melt cooling rate is less than 40°C/sec, larger compounds crystallize, resulting in insufficient compounds in the above-mentioned defined size range, so that the recrystallized particles are not fine, and excellent moldability cannot be obtained. In addition, when the cooling rate is greater than 90°C/sec, fine compounds crystallize, resulting in the reduction of compounds in the above-mentioned defined size range, so that fine recrystallized particle plates cannot be obtained.

The slabs obtained from the twin-strip casting process are cold rolled to form slabs of the desired thickness, followed by solution heat treatment and recrystallization. At this time, in the cold rolling step, annealing may be provided, but the solution heat-treated cold-rolled sheet has a cooling shrinkage of at least 55%. Solution heat treatment is performed in a continuous annealing furnace. The heat treatment temperature is at least 500°C, cooled to 100°C, and the cooling rate is at least 1°C/sec. The average size of the recrystallized grains of the cold-rolled sheet after solution heat treatment is 25 μm or less, due to the reduction in the size and number of intermetallic compounds. These boards can be used directly, or passed through the shell channel or about 1-5% of the flattener to obtain a flat surface.

Example

Aluminum alloy melts with the composition in Table 1 were degassed, fixed, and then melt casted into 7mm thick plates with a cooling rate of 50°C/sec in a double-belt continuous casting process. The tensile speed of the thick plate is 8m/min. Cold rolled slabs, then annealed as needed to form 1mm thick slabs. Next, the thick plate is solution heat treated, and then the size and quantity of intermetallic compounds, recrystallized grain size, yield strength (YS) at 0.2% elongation, maximum tensile strength (UTS), elongation (EL), longitudinal The results of tensile height and resistance spot weldability are shown in Table 3.

The longitudinal tensile conditions and the conditions for evaluating the resistance spot weldability are as follows:

(longitudinal tensile test)

The mold used punching diameter 50mm

Shoulder radius 5mm

       Inner diameter of machine head 52.5mm

Shoulder radius 8mm

Blank Diameter 112.5mm

(Resistance Spot Weldability Evaluation Conditions)

Single-phase rectification type spot welding machine

Electrode Cu-1%Cr alloy

Pressure 400kg force

Determination of welding current: the minimum welding current, where the tensile shear strength meets the average standard of Class A determined by JIS Z3140.

Consecutive Welds: The number of consecutive welds having a strength exceeding the Class A average standard when using the above-identified current values and with the above-mentioned welding conditions.

A: At least 500 continuous welding points

B: at least 200, less than 500 continuous welding points

C: less than 200 continuous welding points

Table 1 alloy composition (mass percentage)

Alloy No. Mg Si Fe Mn Cu Zr Ti B Remark A 0.6 0.8 0.12 0.1 - - 0.02 this invention B 0.4 0.8 0.2 0.2 - - 0.02 this invention C 0.5 0.7 0.2 0.2 - - 0.02 this invention D 0.5 0.8 0.2 0.2 - - 0.01 this invention E 0.6 0.8 0.7 0.1 - - 0.02 this invention F 0.5 0.9 0.15 0.3 - - 0.02 this invention G 0.5 0.7 0.2 0.2 0.6 - 0.02 this invention h 0.5 0.7 0.2 0.2 - 0.15 0.02 this invention I 0.5 0.7 0.2 0.2 0.7 0.12 0.02 this invention J 1.2 0.7 0.2 0.2 - - 0.02 comparative example K 0.5 1.4 0.2 0.2 - - 0.02 comparative example L 0.5 0.7 0.05 0.2 - - 0.02 comparative example m 0.5 0.7 1.5 0.2 - - 0.02 comparative example N 0.5 0.7 0.2 0.7 - - 0.02 comparative example o 0.5 0.7 0.2 0.2 1.2 - 0.02 comparative example P 0.5 0.7 0.2 0.2 - 0.5 0.02 comparative example

Note: Other residues: aluminum and impurities

Underlined values indicate outside the scope of the invention

Table 2 Production process

serial number Alloy No. Pouring method/plate thickness (mm) Cooling rate (℃/sec) Hot rolling (mm) Cold rolling (mm) Intermediate annealing temperature (℃/h) Cold rolling (mm) Solution heat treatment temperature (℃) Remark 1 A Double Belt/7 50 - - - 1 550°C this invention 2 B Double Belt/7 50 - - - 1 550°C this invention 3 C Double Belt/7 50 - - - 1 550°C this invention

4 D Double Belt/7 50 - - - 1 550°C this invention 5 E Double Belt/7 50 - - - 1 550°C this invention 6 F Double Belt/7 50 - - - 1 550°C this invention 7 G Double Belt/7 50 - - - 1 550°C this invention 8 h Double Belt/7 50 - - - 1 550°C this invention 9 I Double Belt/7 50 - - - 1 550°C this invention 10 ℃ Double Belt/7 50 - 2.5 360/2 1 550°C this invention 11 B Double Belt/7 75 - - - 1 550°C this invention 12 J Double Belt/7 50 - - - 1 550°C comparative example 13 K Double Belt/7 50 - - - 1 550°C comparative example 14 L Double Belt/7 50 - - - 1 550°C comparative example 15 m Double Belt/7 50 - - - 1 550°C comparative example 16 N Double Belt/7 50 - - - 1 550°C comparative example 17 o Double Belt/7 50 - - - 1 550°C comparative example 18 P Double Belt/7 50 - - - 1 550°C comparative example 19 B Double Belt/20 20 3 - - 1 550°C comparative example 20 B Double Belt/3 150 - - - 1 550°C comparative example

Note: the underlined value indicates that it is beyond the scope of the present invention

Table 3 Microstructure and properties

Note A: At least 500 continuous welding points

B: at least 200, less than 500 welding points

C: less than 200 welding points

The underlined value indicates that it is beyond the scope of the present invention

Recrystallized particle size measured by line intercept method

From the results in Table 3, it can be clearly seen that the examples of the present invention (sample numbers 1-11) have a high longitudinal tensile height and excellent compression formability, while there are many continuous welding points and excellent continuous resistance spot weldability . On the other hand, Comparative Examples (12-18) whose compositions are outside the range of the present invention, have low longitudinal tensile height and poor moldability, although Comparative Examples (Examples 14, 19, 20) have few equivalent circumference diameters of 1 -6 micron intermetallics and large particle sizes have few continuous welds and poor continuous resistance spot weldability.

As described above, according to the present invention, the aluminum alloy plate having excellent compression formability and continuous resistance spot weldability has a good surface quality after being pressed, can be continuously assembled by resistance spot welding, and thus has a high yield. The 6000-type alloy sheet also has a high strength improvement in a baking step after coating or the like, thereby having excellent industrial value in a wide range of applications such as automobile body panels.

Claims (6)

1. An aluminum alloy plate with excellent compression formability and continuous resistance spot weldability, comprising: The mass fraction is 0.3-1.0% of magnesium, 0.3-1.2% of silicon, 0.10-1.0% of iron and 0.05-0.5% of manganese; here iron+manganese≥0.2%; the rest includes aluminum and unavoidable impurities, of which heavy The average grain size of the crystals is 25um or less, and there are at least 5000 grains/mm ² of intermetallic compounds with a circumference equivalent diameter of 1-6um. 2. The aluminum alloy plate having excellent compression formability and continuous resistance spot weldability according to claim 1, further comprising 0.5-1.0% copper. 3. The aluminum alloy plate having excellent compression formability and continuous resistance spot weldability according to claim 1, further comprising 0.1-0.4% zirconium. 4. The aluminum alloy plate having excellent compression formability and continuous resistance spot weldability according to claim 2, further comprising 0.1-0.4% zirconium. 5. The aluminum alloy plate having excellent compression formability and continuous resistance spot weldability according to any one of claims 1-4, further comprising 0.05% or less titanium, or 0.05% or less titanium and 0.01% or less boron. 6. The method for preparing the aluminum alloy plate with excellent molding formability and continuous resistance spot weldability described in any one of claims 1-5, comprising pouring the melt of the above-mentioned components into a pair of forced cooling relative rotating Casting machine for strips; casting melt at a cooling rate of 40-90°C/sec to form a 5-10mm thick slab; stretching said slab from the opposite side of the melt pouring gate; direct rolling or winding into coils ; followed by solution heat treatment.