WO1995014113A1

WO1995014113A1 - Aluminium-silicon-magnesium alloy having improved ductility and deep-drawing properties, and method for producing same

Info

Publication number: WO1995014113A1
Application number: PCT/FR1994/001330
Authority: WO
Inventors: Jean-Christophe Ehrstrom; Daniel Ferton; Christophe Sigli
Original assignee: Pechiney Rhenalu
Priority date: 1993-11-17
Filing date: 1994-11-15
Publication date: 1995-05-26
Also published as: FR2713664B1; CA2152402A1; KR960700353A; DE69418855T2; FR2713664A1; EP0679199B1; JPH08505904A; CA2152402C; BR9406554A; DE69418855D1; EP0679199A1

Abstract

Aluminium-silicon-magnesium alloys having improved ductility and deep-drawing properties for use as sheet or strip, and a method for producing same, are disclosed. The sheet or strip is particularly suitable for deep-drawing and motor vehicle bodywork in particular. The claimed alloy has a chemical composition consisting of: 0.1-0.8 wt % Mn, 0.25-0.8 wt % Mg, 0.5-1.3 wt % Si, up to 0.9 wt % Cu, up to 0.5 wt % Fe, and other elements up to 0.5 wt % each and 0.15 in all, with the balance being Al. The sheet and strip are produced by casting, hot rolling under special reheating and rolling conditions, cold rolling, age-hardening, forming and curing of coatings, and optionally pre-tempering performed between quenching and age-hardening.

Description

ALLOY OF AI_UMIOTXIM-SILICC TYPE ^ ^ MAGNESIUM WITH DUCTILITY AND EMI_OOTISSABILITY ALV_EîLIOREES AND PROCESS FOR OBTAINING

The invention relates to aluminum alloys of the Al-Si-Mg type with improved ductility and stampability, used in the form of sheets or strips, as well as a process for obtaining these. The sheets or bands are particularly intended for stamping and in particular for the automobile body.

For a given mechanical strength, ductility and drawability are the essential characteristics of sheets or strips intended to be cold formed, before surface coatings such as painting and "baking" thereof.

The conventional alloys used in this field, such as alloys 6009, 6016, 6111, according to the designation of the Aluminum Association still exhibit insufficient mechanical characteristics of use and formability.

The alloy according to the invention contains (by weight%): from 0.1 to 0.8 Mn from 0.25 to 0.8 Mg from 0.5 to 1.3 Si up to 0.9 Cu up to at 0.5 Fe up to 0.5 (each) and 0.15 (total) of other elements remains: Al.

However, a preferred composition is as follows: from 0.15 to 0.65 Mn from 0.3 to 0.6 Mg from 0.7 to 1.2 Si from 0.1 to 0.5 Cu up to 0.4 Fe remains Al + unavoidable impurities. The preferred composition is as follows: from 0.25 to 0.45 Mn from 0.3 to 0.5 Mg from 0.85 to 1.10 Si from 0.1 to 0.3 Cu to 0.3 Fe rest: A1 + unavoidable impurities.

It is known that the presence of Mn is favorable to mechanical strength and to deformability; this action is sensitive beyond 0.1%; however, above 0.8% Mn, coarse compounds (Al, Mn, Fe) are formed which impair formability. The Applicant has also found that high contents of Mn lead to homogenization of the microscopic deformation, which is favorable to a good distribution of the deformations.

For values of Mg less than 0.25%, the elastic limit after curing of the coatings is too low; for values greater than

0.8%, formability becomes insufficient and maturation too fast.

If the Si content is less than 0.5%, the mechanical characteristics are too low; if Si> 1.3%, coarse primary compounds appear and impair formability.

If the Cu content is greater than 0.9%, the corrosion resistance

(intercrystalline) is insufficient.

If the Fe content is greater than 0.5%, this results in coarse precipitation which is detrimental to formability. -

The manufacturing process usually used includes the following operations:

- casting of an alloy of given composition in the form of ingots or strips

- possible homogenization

- reheating and hot rolling

- cold rolling

- dissolution

- mi is cold formed in the T4 state

- possible surface coating and its "cooking", for example a paint (which contributes to the hardening of the alloy) - see example US 4614552, US 4784921, US 4840852, WO 87/02712.

The Applicant has found that this range could be simplified and / / improved, on the one hand by reducing the homogenization step to reheating before hot rolling, or on the other hand, by introducing a rapid quenching and a pre- returned after quenching and maturing.

Thus, the process according to the invention, comprising the casting operations reheating, hot rolling and possibly cold rolling, soluti and quenching, maturation and possibly "baking" surface coating thereof, is characterized in that the temperature reheating before hot rolling and the inlet temperature to the hot laminate is between 460 and 520 ° C.

A rise in temperature at a speed of between 10 ° C / h and 150 ° C and a limited holding temperature between 460 ° C and 520 ° C lead effect to a maximum of the volume density of the precij stes, Mn Al (Fe , Mn) If their maximum size is less than 0.2 "m and their median tail is less than 0.07" m.

After the temperature has risen, the temperature holding time e is between 30 min and 24 h. The temperature at the end of hot rolling is preferably less than 400 ° C. and even 350 ° C.

The fine manganese precipitates remain until the final stage, and the applicant hypothesizes that the presence of these is at the origin of the improvement of the cold forming characteristics.

The dissolution is preferably carried out between 520 and 570 ° C and in particular, between 550 and 570 ° C, for 5 min to 1 h. The average quenching speed is preferably greater than 100 ° C / sec.

For short holding times, a pass-through oven can be used Typically the alloy matures at room temperature and reaches a stationary hardness in about 15 days, a state in which it is capable of undergoing shaping.

After forming and optionally a surface coating, the alloy can undergo a hardening by tempering during the baking treatment of the coating (around 180 ° C. for 30 min). It has however been noted that in the case of an alloy homogenized in a conventional manner, the practice of a pre-annealing between 70 and 150 ° C for 0.5 to 5 h after quenching leads to a significant increase in the coefficient d 'hardening n (after maturation) and a significant increase in the mechanical strength characteristics (after curing of the coatings). The coefficient of work hardening is equal to n = d (Lnςr -) / d £. , <j— being the constraint of Von Misés et cl. the equivalent Von Mises deformation for tensile deformations between 5 and 20% (C = Ln (l / lo)).

FIG. 1 represents the changes in the work hardening coefficient n in the ripened state as a function of the elastic limit in the hardened state with and without pre-tempering, under the conditions reported in Example 2.

The invention will be better understood using the following examples:

Example 1

The alloys whose composition is given in Table I have been

2 prepared in ingots, 1.25x0.6 m in section, scalped, reheated

(rise speed: 46 ° C / h; holding temperature: 480 ° C) and hot rolled with an inlet temperature of 480 ° C and an outlet temperature of 310 ° C up to a thickness of 4mm, then cold to a thickness of 1.2mm.

The dissolution in a passing oven was carried out under the conditions given in Table II, mist cooling and then the sheets were aged for 15 days at room temperature before testing.

Mechanical characteristics (long sense) and breaking strains. f biaxial expansion obtained are shown in Table III. The biaxial expansion test consists in deforming a 300x300x1.2 mm sheet held by a circular blank with a diameter of 250 mm by hydraulic pressure. The deformation is measured at the top of the dome formed. It can be seen that the alloy according to the invention has improved formability characteristics compared to those of the alloys obtained according to the prior art. There is also a slight hardening which is not specifically sought in the invention.

The Mn precipitates have a median size at 0.06 nm with a maximum dimension of 0.18 µm. *

TABLE I

TABLE II

TABLE III

* according to the invention.

Example 2

An alloy with the following weight composition (in%)

Si: 1.08 Fe: 0.10 Cu: 0.05 Mn: 0.38 Mg: 0.40 was poured into 1.25 x 0.6 m trays, homogenized at 520 ° C for

33 h, hot rolled up to 4 mm thick between 494 and 304 ° C, cold rolled up to 1.2 mm thick, dissolved in an air oven with rise in 30 min at 560 ° C and maintained for 5 min at this temperature and quenched with water at 20 ° C

10 min after quenching, samples underwent a pre-annealing of 2 h at

100 ° C, other comparison samples not being treated.

The tensile tests were carried out 14 days after quenching and certain samples were checked after an income of 30 min at

180 ° C, simulating the cooking conditions of the coatings.

The results obtained are reported in Table IV below and shown graphically in Figure 1.

We can see the beneficial effects of pre-tempering on the coefficient n in the matured state (T4) and on the mechanical characteristics after curing of the coatings.

Example 3

Products were treated in accordance with Example 2, except for different cooling rates during quenching.

The results obtained are reported in Table V.

TABLE V

580 140 I 271 I 32.4 I 24.4 I 161

1

It can be seen that the high quenching speeds are clearly favorable for obtaining high mechanical characteristics in the hardened state, 0 with an increase in the elongation distributed in the T4 state.

Claims

1. Aluminum alloy for strips and sheets intended for stamping, characterized in that it contains by weight%: from 0.1 to 0.8 Mn from 0.25 to 0.8 Mg from 0.5 to 1 , 3 If up to 0.9 Cu up to 0.5 Fe up to 0.5 (each) and 0.15 (total) of other elements remains Al.

2. Alloy according to claim 1 characterized in that it contains: from 0.15 to 0.65 Mn from 0.3 to 0.6 Mg from 0.7 to 1.2 Si from 0.1 to 0.5 Cu up to 0.4 Fe.

3. Alloy according to claim 2 characterized in that it contains: from 0.25 to 0.45 Mn from 0.3 to 0.5 Mg from 0.85 to 1.10 Si from 0.1 to 0.3 Cu up to 0.3 Fe.

4. Alloy according to one of claims 1 to 3 characterized in that it contains precipitates with Mn, type Al (Mn, Fe) Si, whose median size is less than 0.07 ”m and the maximum size less at 0.20 ”m.

5. Method for obtaining sheets or strips of Al alloy according to one of claims 1 to 4, comprising heating and hot rolling (and optionally cold), dissolving and quenching and maturing at the ambient temperature characterized in that the temperature for reheating and the start of hot rolling is between 460 and 500 ° C.

6. Method according to claim 5 characterized in that the duration of temperature maintenance is between 30 min and 48 h.

7. Method according to one of claims 5 or 6 characterized in that the rate of temperature rise is between 10 ° C / h and 150 ° C / h.

8. Method according to one of claims 5 to 7 characterized in that the end temperature of hot rolling is less than 400 ° C, and preferably less than 350 ° C.

9. Method according to one of claims 5 to 8 characterized in that the dissolution takes place between 520 and 570 ° C, for 5 min to 1 h.

10. Method according to one of claims 5 to 9 characterized in that the ambient maturation is at least 15 days.

11. method for obtaining sheets or strips of Al alloy according to one of claims 1 to 4 comprising at least one homogenization or reheating of the ingots, hot rolling (and possibly cold), dissolving and quenching , a maturation, a shaping and a baking treatment of the coatings characterized in that a pre-tempering is practiced between the quenching and the maturation.

12. Method according to rev.ll characterized in that the pre-annealing is carried out in a temperature range from 70 to 150 ° C, for a period of between 0.5 and 5 hours.

13. Method for obtaining a sheet or strip of Al alloy according to one of claims 11 or 12 characterized in that the average cooling rate during quenching is greater than 100 ° C / sec