CN114829644A

CN114829644A - Improved method for producing a structural component for a motor vehicle body

Info

Publication number: CN114829644A
Application number: CN202080087196.6A
Authority: CN
Inventors: E·穆勒; B·乌赛克; D·巴尔比耶
Original assignee: Constellium Neuf Brisach SAS
Current assignee: Constellium Neuf Brisach SAS
Priority date: 2019-12-17
Filing date: 2020-12-15
Publication date: 2022-07-29
Also published as: US20230008838A1; EP3839085A1; EP3839085B1; EP4077753A1; JP2023506278A; WO2021122621A1; CA3162027A1; KR20220113793A

Abstract

Disclosed is a method for producing a rolled product for automobile bodies or body structures from an alloy comprising Si: 0.75-1.10, Fe: up to 0.4, Cu: 0.5-0.8, Mn: 0.1-0.4, Mg: 0.75-1, Ti: maximum 0.15, Cr: maximum 0.1 and V: up to 0.1. The various possibilities of pre-ageing the plates and heat treatment of the component provide advantageous material properties in terms of shaping, material strength and low susceptibility to bake hardening processes that can vary depending on the position of the component in the vehicle body.

Description

Improved method for producing a structural component for a motor vehicle body

Technical Field

The present invention relates to the field of structural motor vehicle parts or components, also known as "body in white", which are manufactured in particular by stamping of Aluminium alloy sheets, more particularly alloys of the AA6 xxx-series according to the designation Aluminium Association (Aluminium Association), intended to absorb energy irreversibly upon impact, and having an excellent compromise between high mechanical strength and good impact properties, such as in particular impact absorbers or "crash boxes", reinforcing parts, linings or other structural vehicle body parts.

More specifically, the invention relates to the manufacture of such parts by stamping in the solution hardened, quenched and naturally age tempered condition, followed by a localized age hardening and paint or "bake hardening" treatment.

Background

Aluminum alloys are increasingly used in automotive construction to reduce the weight of vehicles, thereby reducing fuel consumption and greenhouse gas emissions.

Aluminum alloy panels are used in particular for the production of many parts of the "body-in-white", among which are body skin parts (or exterior body panels), such as front wings, roofs, hoods, trunks or door skins, and lining parts or body structural components, such as doors, hoods, tailgates or roof linings or reinforcements, or spars, bulkheads, load-bearing floors, bushings (tunnels) and front, center and rear pillars, and finally impact absorbers or "crash boxes".

Converting steel to aluminum for liners or structural components with complex geometries becomes even more problematic if many skin components have been made from aluminum alloy sheets. Firstly, this is due to the less good formability of aluminium alloys compared to steel and secondly, to the mechanical properties that are generally inferior to those of steels for parts of this type.

This is because this type of application requires a range of performances that sometimes conflict with each other, such as:

high formability in the delivery state, i.e. state T4, in particular for punching operations,

-controlled tensile yield strength at delivery conditions of the sheet to control spring back upon forming,

good performance in various assembly methods for automotive bodies, such as spot welding, laser welding, adhesive bonding, rivets (clinging) or rivets (rivetting),

high mechanical strength after electrophoresis and paint baking to obtain good mechanical strength in use, while minimizing the weight of the parts,

good energy absorption capacity in the event of an impact, to be suitable for vehicle body structural parts,

good corrosion resistance, in particular intergranular, stress and filiform corrosion resistance of the finished part,

compliance with the requirements of recycling manufacturing waste or recycling vehicles,

acceptable mass production costs.

However, there are now indeed mass-produced motor vehicles with body-in-white which consist predominantly of aluminum alloys. For example, Ford F-150 model 2014 edition consists of AA6111 structural alloy. This alloy was developed by the aluminum group of canada (Alcan group) in the year 1990-1980-. Two references describe this development:

form et Al, "optimized Al alloy for auto body sheet applications", SAE technical conference, 3 months 1984, describing the following composition: si: 0.85; fe: 0.20; cu: 0.75; mn: 0.20 and Mg: 0.72.

bull et Al, "Al sheet alloys for structural and skin applications", proceedings of the 25 th ISATA, article 920669,1992, 6 months.

The main property is still high mechanical strength, even if it was originally designed to withstand indentation for skin type applications: "yield strength of 280MPa after 2% prestrain and 30 minutes at 177 ℃).

In addition, other alloys of the AA6 xxx-series have been developed for aerospace or automotive applications with high mechanical properties. Thus, alloys of the AA6056 type, whose development dates from Pechiney to the 80 th of the 20 th century, have been the subject of many projects and numerous publications to optimize mechanical properties or to improve resistance to intergranular corrosion. This is the subject of a patent application (WO 2004/113579A 1).

AA 6013-type alloys have also been the subject of a number of projects. For example, in Alcoa, published application US 2002/039664 in 2002, the T6 temper used contains 0.6-1.15% Si; 0.6-1% Cu; 0.8-1.2% Mg; 0.55-0.86% Zn; less than 0.1% Mn; an alloy of 0.2-0.3% Cr and about 0.2% Fe will have good intergranular corrosion resistance and Rp of 380MPa _0.2 And (4) combining.

In Aleris, application WO 03006697 published in 2003 relates to alloys of the AA6xxx series containing 0.2% to 0.45% Cu. The object of the invention is to propose an AA 6013-type alloy with a reduced Cu content, with the aim of an Rm in the T6 temper of 355MPa and a good resistance to intergranular corrosion. The claimed composition is as follows: 0.8-1.3% of Si, 0.2-0.45% of Cu; 0.5-1.1% Mn; 0.45-0.1% Mg.

Structural components for automotive applications made of 7xxx alloys, such as described in application EP 2581218, are also known.

Furthermore, in order to produce parts with complex geometries from aluminium alloys, such as door liners, which cannot be realized by conventional stamping using the above-mentioned alloys, various solutions have been conceived and/or implemented in the past:

the difficulty associated with stamping is circumvented by preparing parts of this type, and in particular parts of the "pressed" type, by moulding. This is demonstrated by the patent EP 1305179B 1 to Nothelfer GmbH, which has priority in 2000.

So-called "warm" stamping to benefit from better forming suitability. This involves heating the aluminium alloy billet, wholly or locally, to a so-called intermediate temperature (i.e. 150 ℃ to 350 ℃) to improve its properties under pressure, and possibly also to preheat its tooling. The applicant's patent EP 1601478B 1, which has priority in 2003, is based on this solution.

Stamping suitability of the AA5 xxx-series alloy itself by compositional modification; it is particularly recommended to increase the magnesium content to more than 5%. But this is not neutral in terms of corrosion resistance.

-using composite plates consisting of an AA5 xxx-series alloy core with a magnesium content exceeding 5% for better formability, and of a cladding panel made of a more corrosion-resistant alloy. However, the corrosion resistance at the edges of the plate, the stamped area or more generally the area where the core is exposed, and in particular in the assembly, may prove to be insufficient.

Furthermore, document EP 1702995 a1 describes a method for producing aluminum alloy sheets, which comprises supplying a molten aluminum alloy having a chemical composition, in weight percent, of Mg: 0.30 to 1.00%, Si: 0.30 to 1.20%, Fe: 0.05 to 0.50%, Mn: 0.05 to 0.50%, Ti: 0.005 to 0.10%, optionally selected from Cu: 0.05 to 0.70% and Zr: 0.05 to 0.40%, and the balance Al and unavoidable impurities: casting the molten alloy into a sheet having a thickness of 5 to 15mm by a twin-belt casting method at a cooling rate of 1/4 of a sheet thickness of 40 ° to 150 ℃/s, coiling in the form of a coil, homogenizing, cooling the resultant coil to a temperature of 250 ℃ at a cooling rate of at least 500 ℃/h or more, then cold rolling, and then solution heat treating. This document does not mention partial ageing after shaping.

The invention-W02018/185425 relates to a method for preparing a stamped component of a motor vehicle body or body structure from an aluminium alloy, said method comprising the steps of: metal plates or strips with a thickness of 1.0 to 3.5mm are prepared in an alloy with the following composition (wt%): si: 0.60-0.85; fe: 0.05-0.25; cu: 0.05-0.30; mn: 0.05-0.30; mg: 0.50-1.00; ti: 0.02-0.10; v: 0.00-0.10 and Ti + V ≦ 0.10, the other elements each <0.05 and the total <0.15 and the remainder being aluminium and Mg < -2.67x Si +2.87, dissolving and soaking, pre-tempering, curing for 72 hours to 6 months, stamping, tempering at a temperature of about 205 ℃ and holding time 30 to 170 minutes, or tempering under time-temperature equivalent conditions, painting and "bake hardening" the paint at a temperature of 150 to 190 ℃ for 15 to 30 minutes. The invention also relates to a stamped component of a motor vehicle body or body structure (also referred to as "body-in-white") produced by said method.

US20180119261 describes a6xxx series aluminium alloy with unexpected properties and a new process for making the aluminium alloy. The aluminum alloy has high formability and exhibits high strength. The alloy is prepared by continuous casting and may be hot rolled to final thickness and/or final condition. The alloy may be used in automotive, transportation, industrial, and electronic applications, to name a few.

US20180171452 discloses high strength, highly deformable aluminium alloys and methods of making and processing the alloys. More specifically, a heat treatable aluminum alloy exhibiting improved mechanical strength and formability is disclosed. Processing methods include casting, homogenization, hot rolling, solutionizing, pre-aging, and in some cases pre-straining. In some cases, the processing step may also include cold rolling and/or heat treatment.

In view of the increasing development in the use and mass production of aluminum panels for automotive body components, there is still a need for further improved grades enabling a reduction in thickness without compromising other properties, thereby always improving weight saving.

The problems raised

The aim of the invention, which is to achieve an excellent compromise between formability and high mechanical strength in the T4 temper and good properties of the finished part under riveting and in impact, is achieved by proposing a method of manufacturing said assembly, said method comprising forming in the T4 temper after natural ageing at ambient temperature, and then optionally age-hardening and baking or bake-hardening the formed part. A problem is also to obtain a process which is short and economically advantageous and which is improved compared to products made of alloy AA 6111.

These components must also have very good corrosion resistance and good performance in various assembly methods, such as spot welding, laser welding, adhesive bonding, rivets or rivets.

Object of the Invention

One object of the present invention is a method for manufacturing a rolled product for automotive bodies or body structures (also called "body-in-white") from an aluminium alloy, comprising the following successive steps:

a. ingots having the following composition (wt.%):

Si：0.75–1.10；

fe: up to 0.4;

Cu：0.5–0.8；

Mn：0.1–0.4；

Mg：0.75–1；

ti: up to 0.15;

cr: up to 0.1;

v: up to 0.1;

unavoidable elements and impurities each up to 0.05% and in total up to 0.15%;

the rest of the aluminum alloy is aluminum,

b. the homogenization of the ingot is carried out,

c. hot rolling of an ingot is carried out,

d. cold-rolling the mixture into a plate,

e. solution heat treatment, quenching of the plate,

f. the pre-ageing of the plate is carried out,

g. and (5) naturally aging the plate.

Another object of the invention is a rolled product obtainable by the method of the invention.

Another object of the invention is a component obtainable by the method of the invention.

Another object of the invention is the use of said parts in a motor vehicle as follows: as body skin components (or exterior body panels), for example front wings, roofs, hoods, trunks or door skins, and lining components or body structural components, for example doors, hoods, tailgates or roof linings or reinforcements, or spars, bulkheads, load-bearing floors, bushings and front, center and rear pillars, and finally impact absorbers or "crash boxes".

Drawings

Fig. 1 depicts a device for a "three-point bending test" consisting of two rolls R and a punch B of radius R for bending a rolled product T of thickness T.

Fig. 2 depicts a rolled product T having an inner angle β and an outer angle after a "three-point bending" test, the measurement results α of which are recorded in the accompanying results. The maximum intensity during the test method is also recorded.

Fig. 3 depicts a specific embodiment of the method:

1: uncoiler

2: coiling machine

3: board

4: solid solution smelting furnace

5: quenching unit

6: surface treating machine

7: pre-aging oven

8: storage volume

Detailed Description

Unless otherwise defined in this specification, a general term is defined as NF EN 12258-1. The plate is a flat rolled product with a rectangular cross section with a uniform thickness between 0.20mm and 6 mm.

Unless stated to the contrary, all aluminum alloys described below are named by the name defined by the aluminum association in its regularly published series of registration records.

All indications relating to the chemical composition of the alloy are expressed as weight percentages based on the total weight of the alloy.

Unless defined otherwise herein, the definition of metallurgical state is shown in european standard EN 515.

Static tensile mechanical Properties, in other words, ultimate tensile Strength R _m Tensile yield strength Rp at 0.2% elongation _0.2 And elongation at break A%, determined by tensile testing according to NF EN ISO 6892-1.

The bending angle was determined by means of a three-point bending test according to NF EN ISO 7438 and methods VDA 238-.

Tortuosity is also measured using standard ASTM E290-97 a.

The inventors have selected a range of aluminum alloy compositions in combination with a suitable method that provides the automotive manufacturer with meaningful properties for the part being made.

The subject of the invention is a method for producing a rolled product for automobile bodies or body structures (also called "body-in-white") from an aluminium alloy, said method comprising the following steps. Ingots having the following composition (wt.%):

si: 0.75-1.10. preferably, the Si content is up to 1.0%, and more preferably, the Si content is up to 0.95%.

Fe: up to 0.4. Preferably, the minimum Fe content is 0.15% and/or the maximum Fe content is 0.30%.

Cu: 0.5-0.8. preferably, the ingot has a maximum Cu content of 0.70% and/or a minimum Cu content of 0.55%. More preferably, the maximum Cu content is 0.65%. For economic reasons, it is interesting to limit Cu to 0.8%, 0.70% and even 0.65%, since Cu is generally more expensive than aluminum. It is also advantageous to make the recyclability of the material cheaper. It can also improve corrosion resistance. However, in another embodiment, the Cu content is 0.65% minimum, particularly to increase strength.

Mn: 0.1-0.4. preferably, the maximum Mn content is 0.35% and/or the minimum Mn content is 0.24% or preferably 0.25%. The addition of Mn improves the bending properties in particular.

Mg: 0.75-1, preferably the minimum content of Mg is 0.80% and/or the maximum Mg content is 0.90%.

Ti: up to 0.15, preferably a minimum Ti content of 0.01% and/or a maximum Ti content of 0.05%.

Cr: up to 0.1 and preferably Cr is an unavoidable element or impurity.

V: up to 0.1 and preferably V is an unavoidable element or impurity.

And unavoidable elements and impurities each up to 0.05% and a total of up to 0.15%, and the balance aluminum.

The cast article may be made by various casting methods. Continuous casting, typically horizontal casting, is possible. It is also preferred to use vertical semi-continuous casting, which is also known as direct chill casting. Vertical semi-continuous casting is preferred because it is more uniform across the thickness of the plate.

The ingot is homogenized, hot rolled and cold rolled into a sheet. The plate is subjected to solution heat treatment and quenching. Preferably, the homogenization treatment of the ingot is at a temperature of 520 to 560 ℃, preferably 2 to 8 hours. Preferably, the hot rolling rolls the ingot into a rolled intermediate product having a thickness of 3 to 10 mm. Preferably, the cold rolling rolls the rolled intermediate product into a sheet having a thickness of 1 to 4 mm. The sheet is then solution heat treated, typically at a temperature above the solvus temperature of the alloy, while avoiding incipient melting. Preferably, the solution heat treatment temperature is from 530 ℃, preferably 540 ℃ to 580 ℃, for a time preferably 1 second to 5 minutes. The plate is then quenched. The water quenching is suitably carried out at a temperature of about 15 to 60 c, preferably 15 to 40 c. The pre-ageing is carried out at a temperature of preferably 50 to 120 ℃ for preferably at least 8 hours. Then natural aging is carried out. Natural aging is defined in NF EN 12258-1 and room temperature is defined in NF EN ISO 6892-1. Preferably, the duration of natural aging is 72 hours to 6 months.

The pre-ageing step is preferably carried out by coiling the sheet at coiling temperature and open-air cooling at room temperature.

A convenient continuous annealing line arrangement for achieving pre-ageing is shown in figure 3. The sheet 3 is unwound by means of an unwinder 1 and passes through a solutionizing furnace 4 and a quenching unit 5, after which the sheet 3 enters a surfacing machine 6, a very common step for vehicle body panels, then a pre-ageing oven 7, and finally wound on an open-air winder 8. Thus, at the outlet of the pre-ageing oven 7, the board is hot and the board is reeled on the open-air reel 2 at the reeling temperature. The curl plate 8 is hot and stored in the factory at ambient temperature and cooled to ambient temperature. Pre-ageing takes place during this cooling. The natural ageing starts after the end of the cooling of the curl plate 8, preferably with a pre-ageing duration of at least 8 hours.

Preferably, the pre-ageing is obtained by: the board is coiled at a coiling temperature of 50 to 120 ℃, preferably 60 to 120 ℃, and the coiled board is then cooled open air and has a duration of at least 8 hours.

The rolled products of the invention include products obtainable by the above-described process from casting to natural ageing. The rolled product temper after natural aging was T4.

The tensile yield strength of a rolled product in the T4 temper varies by less than 5MPa, preferably 3MPa, between the tensile yield strength in the transverse direction and the 45 ° direction in the same rolled product. The same plate is defined as a rolled product made from the same ingot, the same homogenization, the same hot and cold rolling, the same solution heat treatment, the same quenching, the same pre-aging, the same natural aging, and the tensile test specimen is cut as close as possible to the rolled product. This is a useful property for part stamping.

Rolled products in the T4 state can be characterized in 6 other specific states T8A, T8C, T8D, T6B, T6C and T8D, which evaluate the material properties of the part.

The T8A, T8C, and T8D temper were achieved by applying 2% strain on the T4 rolled product, followed by specific heat treatments, respectively. The T8A temper was applied using a bake hardening heat treatment at a temperature of 180 ℃ for 20 minutes. The T8C temper used a light short bake hardening heat treatment at 160 ℃ for 5 minutes. The T8D temper used a light and long bake hardening heat treatment at a temperature of 160 ℃ for 20 minutes.

The T6B, T6C, and T6D temper were achieved by specific heat treatment of the T4 rolled product. The T6B temper was applied with a heat treatment at a temperature of 225 ℃ for 30 minutes. The T6C temper used a light short bake hardening heat treatment at 160 ℃ for 5 minutes. The T6D temper was applied with a light and long bake hardening heat treatment at a temperature of 160 c for 20 minutes.

The T4 rolled product can then be shaped, in particular by stamping, to obtain a shape. Optionally, the shape is subjected to an aging treatment. The shapes can be painted and bake hardened into parts at a temperature of 150 to 190 ℃ and preferably 170 to 190 ℃ in 5 to 30 minutes, preferably 15 to 30 minutes.

An object of the present invention is a part obtainable with the rolled product of the present invention by the above-described method. The component may be used in automobiles as a body skin component (or exterior body panel), such as a front wing, roof, hood, trunk or door skin, and a lining component or body structural assembly, such as a door, hood, tailgate or roof lining or reinforcement, or preferably a spar, bulkhead, load floor, sleeve, and front, middle and rear pillars, and finally an impact absorber or "crash box".

In the first embodiment, the coiling temperature is 50 ℃ to 95 ℃ and does not include 95 ℃, preferably 60 to 95 ℃ and does not include 95 ℃. The T4 temper rolled product of this first embodiment is characterized by a tensile yield strength of less than 165MPa, which is useful for the formability of the customer at stamping. As formally stated, the minimum tensile yield strength of the T6B temper rolled product of this first embodiment is 345MPa, and preferably the minimum tensile yield strength is 350 MPa.

The preferred composition of the process according to the first embodiment is:

si: 0.75-1.10, and more preferably less than 0.95%;

fe: up to 0.4, and more preferably 0.15% to 0.30%;

cu: 0.5 to 0.70, and preferably 0.5 to 0.65;

Mn：0.1–0.4；

Mg：0.75–1；

Ti：0.01–0.05；

cr: up to 0.1;

v: as impurities;

With this preferred composition and with a coiling temperature of 50 ℃ to 95 ℃ and excluding 95 ℃, preferably 60 ℃ to 95 ℃ and excluding 95 ℃, the tortuosity of the T4 rolled product of the first embodiment is at most 0.19. This is advantageous in the forming of the part.

A more preferred composition of the first embodiment is:

si: 0.75-1.10, and more preferably less than 0.95%;

fe: up to 0.4, and more preferably 0.15% to 0.30%;

cu: 0.5 to 0.70, and preferably 0.5 to 0.65;

mn: 0.24-0.30, and preferably a minimum of 0.25%;

Mg：0.75–1；

Ti：0.01–0.05；

cr: at most 0.1;

v: as impurities;

With this more preferred composition, combined with a coiling temperature of 50 ℃ to 70 ℃, preferably 60 ℃ to 70 ℃, the VDA angle of the rolled product in the T4 temper is greater than 125 °. The T4 rolled product has a tortuosity of less than 0.19. This may be useful in some stamping applications.

In another preferred method of the first embodiment, the coiling temperature is 70 ℃ to 95 ℃. In this way, the minimum tensile yield strength of the rolled product in the T8A temper was 275 MPa. In a more preferred method of this embodiment, the minimum tensile yield strength of the rolled product in the T8A temper is 280MPa, and the coiling temperature is 70 ℃ to 95 ℃, and the composition is such that

Si: 0.75-1.10, and more preferably less than 0.90%;

fe: up to 0.4, and more preferably 0.15% to 0.30%;

Cu：0.65–0.8；

mn: 0.1-0.4, and more preferably less than 0.24%, and a minimum of 0.15%;

mg: 0.75-1, and more preferably less than 0.95%;

Ti：0.01–0.05；

cr: up to 0.1;

v: as impurities;

In the second embodiment of the present invention, the coiling temperature is 95 ℃ to 120 ℃, and preferably 95 ℃ to 105 ℃, and preferably consists of:

si: 0.75-1.10, and more preferably less than 0.90%;

fe: up to 0.4, and more preferably 0.15% to 0.30%;

cu: 0.5 to 0.70, and preferably 0.5 to 0.65;

mn: 0.1-0.4, and preferably a minimum of 0.25%, and preferably less than 0.35%;

Mg：0.75–1；

Ti：0.01–0.05；

cr: up to 0.1;

v: as impurities;

The advantage of this second embodiment is in particular the low sensitivity of the yield strength of the part to changes in the bake hardening process. The bake hardening conditions are dependent on the location inside the body assembly, so components with low sensitivity to the bake hardening conditions are advantageous because of greater flexibility for the automotive manufacturer. This low sensitivity can be evaluated by comparing the performance of the T6C state with the performance of the T6D state and/or the performance of the T8C state with the performance of the T8D state (which are obtained from the same T4 state rolled product).

For the rolled products obtained by the method of the second embodiment, the tensile yield strengths of the rolled products of the T8C and T8D temper and made from the same rolled product of the T4 temper differed by less than 5 MPa. The samples of the T8C and T8D rolled products differ only in the duration of the bake hardening, which is 160 ℃ in each case.

The T6C and T6D rolled product samples differed only in the duration of the bake hardening temperature of 160 ℃. For the rolled products obtained by the method of the second embodiment, the tensile yield strengths of the rolled products of the T6C and T6D temper and made from the same rolled product of the T4 temper differed by less than 5 MPa.

More generally, the rolled product may be heat treated at a temperature of 150 to 190 ℃ and preferably 170 to 190 ℃ for 5 to 30 minutes, preferably 15 to 30 minutes. The yield strength of the heat treated rolled product at a given temperature within the above temperature range for any duration within the above duration range varies by less than 15MPa, preferably 10MPa and more preferably 5 MPa.

More generally, the rolled product at 2% strain may be heat treated at a temperature of 150 to 190 ℃ and preferably 170 to 190 ℃ for 5 to 30 minutes, preferably 15 to 30 minutes. The yield strength variation of the heat treated 2% strained rolled product at a given temperature within the above temperature range for any duration within the above duration range is less than 15MPa, preferably 10MPa and more preferably 5 MPa.

For the second embodiment, the maximum tensile yield strength of the rolled product in the T4 temper was 190 MPa. For the second embodiment, the minimum tensile yield strength of the T6B temper rolled product was 340 MPa. For the second embodiment, the minimum tensile yield strength of the T8A temper rolled product is 280MPa, preferably 290 MPa.

The recyclability of any alloy is an important technical and economic parameter. Reducing the range of any element is useful to enhance the recovery process as this provides predictability of future melts. Reducing the maximum amount of added elements is also advantageous because they can be more expensive than aluminum. Reducing the Si content facilitates recovery since in many alloys this element is both an impurity and detrimental to the properties of the aluminium product. An advantageous embodiment of the invention is therefore to reduce the Si content to a maximum of 0.95%. Further advantageous embodiments are a reduction of the maximum amount of Fe to 0.30% and/or an increase of the minimum amount of Fe to 0.15%. Another advantageous embodiment is to reduce the Cu maximum to 0.70%, and preferably to 0.65%, and/or to increase the Cu minimum to 0.55%. Another advantageous embodiment is to reduce the maximum content of Mn to 0.35%, and more preferably to 0.30%, and/or to increase its minimum content to 0.15%, and more preferably to 0.25%. Another embodiment is also to reduce the maximum content of Ti to 0.05% and/or to increase the minimum content to 0.01%. Another embodiment is to classify V as a maximum of 0.05% impurity.

All these combinations of alloy compositions and coiling temperatures of the present invention provide many possibilities for automotive manufacturers to have different formability properties. The automobile manufacturer may also optimize its tooling and the design of its components. Shape aging allows for high strength parts, but it requires a specific heat treatment for shape aging. High strength alloys are beneficial for lightweight components. If the component does not require high strength materials, the automotive manufacturer can avoid form aging, which is beneficial to simplify production. Thus, the present invention provides flexibility to the automotive manufacturer.

Examples

Introduction to the word

Table 1 summarizes the chemical composition (wt%) of the alloys used during the test. The proportion of other unavoidable elements and impurities is less than 0.05%, the total amount is less than 0.15%, and the balance is aluminium.

Alloy G is an exemplary AA6111 alloy and alloy H is an exemplary modified AA 6056.

Alloy (I)	Si	Fe	Cu	Mn	Mg	Ti	Cr	V
									A	0.81	0.21	0.68	0.20	0.7	0.04	<0.05	<0.05
B	0.81	0.21	0.70	0.20	0.8	0.03	<0.05	<0.05
									C	0.81	0.20	0.58	0.20	0.7	0.03	<0.05	<0.05
D	0.80	0.20	0.58	0.20	0.9	0.04	<0.05	<0.05
									E	0.83	0.19	0.56	0.29	0.8	0.03	<0.05	<0.05
F	0.82	0.20	0.58	0.29	0.9	0.10	<0.05	0.07
									G	0.70	0.20	0.65	0.20	0.7	0.04	<0.05	<0.05
H	0.81	0.20	0.85	0.20	0.7	0.05	<0.05	<0.05

TABLE 1

These rolling ingots of different alloys are obtained by vertical semi-continuous casting. After stripping, these different ingots were subjected to a homogenization heat treatment at 540 ℃ for about 4 hours, and then directly hot rolled into a 5mm intermediate rolled product. The 5mm intermediate rolled product was cold rolled to obtain a sheet having a thickness of 2 mm.

The rolling step is followed by a solution heat treatment and then quenching. The solution heat treatment is carried out at a temperature above the solvus temperature of the alloy while avoiding incipient melting. In this non-limiting example, the solutionizing temperature is 570 ℃. The solutionized sheet was then quenched in water at 20 ℃. The plate samples were coiled at 3 coiling temperatures of 100 ℃, 80 ℃ and 60 ℃, pre-aged for 8 hours, and then naturally aged. Two natural aging were used: 7 days and 30 days at room temperature to obtain rolled products in the T4 temper.

The T4 rolled product was transformed to the T8A temper with 2% strain and then heat treated within 20 minutes using a typical bake hardening heat treatment at 180 ℃. The T8A sample was then characterized.

The T4 rolled product was also heat treated to a T6B temper at 225 ℃ heat treatment in 30 minutes. The T6B sample was then characterized.

Test results

Tensile testing at ambient temperature was carried out according to NF EN ISO 6892-1, using non-proportional test pieces whose geometry is widely used for plates and corresponds to the type of test piece 2 in Table B.1 of appendix B of the standard. These test pieces have in particular a width of 20mm and a calibration length of 120 mm. Tensile tests were carried out on the rolled products in the T4, T8A and T6B temper. The results obtained with a coiling temperature of 80 ℃ and a natural ageing of 30 days are shown in table 2. The results obtained with a coiling temperature of 60 ℃ and a natural aging of 30 days are shown in Table 3. The results obtained at coiling temperatures of 60 ℃, 80 ℃ and 100 ℃ and natural aging for 7 days are shown in Table 4.

TABLE 2

TABLE 3

TABLE 4

The coiling temperature is an important parameter of tensile yield strength in a T4 state. At 60 ℃ and 80 ℃, it is allowed to limit the T4 tensile yield strength to below 165MPa, which is advantageous for automobile manufacturers-if it is desired to maintain ease of stamping (ease).

The tensile yield strength of example alloys B, D, E and F in the T8B temper was at least 350 MPa. The tensile yield strength of these example alloys in the T8A temper was a minimum of 275 MPa.

Reducing the range of Ti to a maximum of 0.05%, V to a maximum of 0.05% of impurities, and Cu to less than 0.65% is also advantageous, as exemplified by alloys E and D, because it reduces the bow to 0.15, which facilitates the manufacturability of the assembly without being affected by the coiling temperature.

In addition to the above-mentioned V, Ti and reduced range of Cu, the optimized range of Mn from 0.25% to 0.35% provides a very favorable 3-point bend test at a coiling temperature of 60 deg.C with a high VDA angle, which is advantageous for formability. This is exemplified by alloy E having a coiling temperature of 60 ℃.

Example 2

The rolled products made with alloy E after 7 days of natural ageing at coiling temperatures of 80 ℃ and 100 ℃ were used for the other tests. The samples at the two coiling temperatures were divided into two groups: in the first group a strain of 2% was applied, while the second group did not have any strain. A bake hardening temperature of 160 ℃ was then applied and the two different durations were 5 minutes and 20 minutes.

These results, provided in table 5 for a coiling temperature of 80 ℃ and in table 6 for a coiling temperature of 100 ℃, show another advantageous embodiment: at a coiling temperature of 100 ℃, the tensile yield strength of the rolled product is almost independent of the bake hardening duration. This is an advantageous property for components that may be installed in a body assembly, whether at the surface or deep inside the assembly of multiple components, because their yield strengths remain similar. This provides flexibility to the component design of the automotive manufacturer.

TABLE 5

TABLE 6

Example 3

Casting an ingot of the following composition

Ingots having the chemical compositions (wt%) in table 7 were cast using a vertical semi-continuous casting method. The proportion of other unavoidable elements and impurities is less than 0.05% and the total amount is less than 0.15%, and the remainder is aluminium.

Si	Fe	Cu	Mn	Mg	Cr	Ti
							0.86	0.21	0.66	0.28	0.85	0.01	0.04

TABLE 7

The rolled ingot was heated at 554 ℃ for 4 hours. The ingot was directly hot rolled. The ingot temperature before the start of hot rolling was 540 ℃. The thickness at the end of hot rolling was 5 mm. The thickness at the end of cold rolling was 2 mm. The plate was divided into three portions to solutionize at three different temperatures 535 ℃, 544 ℃ and above 525 ℃ with different durations respectively: 20s, 45s and 68 s. The plates were quenched in 22 ℃ water. The plates were pre-aged by coiling them at a temperature of 96 ℃ and open-air cooling, and then naturally aged at room temperature of about 20 ℃ for 3 days to obtain rolled products in the T4 temper.

Tensile tests were conducted in the rolling direction (L), the transverse direction (T) of the rolling direction, and the direction (45 °) at 45 ° to the rolling direction.

TABLE 8

Table 8 shows that solution heat treatment is reliable for process variations with respect to temperature or duration to obtain mechanical properties.

The T4 temper tensile yield strength shows that the anisotropy between tensile yield strength in the T and 45 ° directions in the same rolled product is less than 3MPa, as shown in table 8.

The bending radius was also measured in the T6B temper to check the collision behavior of the rolled product. The results are disclosed in table 9.

Table 9.

Claims

1. Method for manufacturing a rolled product for automotive bodies or body structures, also called "body-in-white", from an aluminium alloy, comprising the following successive steps:

a. ingots having the following composition (wt.%):

Si：0.75–1.10；

fe: up to 0.4;

Cu：0.5–0.8；

Mn：0.1–0.4；

Mg：0.75–1；

ti: up to 0.15;

cr: up to 0.1;

v: up to 0.1;

unavoidable elements and impurities each up to 0.05% and in total up to 0.15%;

the rest of the aluminum alloy is aluminum,

b. the homogenization of the ingot is carried out by subjecting the ingot to a homogenization treatment,

c. hot rolling of an ingot is carried out,

d. cold-rolling the mixture into a plate,

e. solution heat treatment, quenching of the plate,

f. the pre-ageing of the plate is carried out,

g. and (5) naturally aging the plate.

2. A method according to claim 1, characterized in that the ingot has a Cu maximum content of 0.70% and/or a Cu minimum content of 0.55%.

3. A method according to any of claims 1-2, characterized in that the ingot has a Mn maximum content of 0.35% and/or a Mn minimum content of 0.15%, preferably 0.24%, and more preferably 0.25%.

4. A method according to any one of claims 1 to 3, characterized in that the ingot has a maximum Ti content of 0.05% and/or a minimum Ti content of 0.01%.

5. The method according to any one of claims 1 to 4, wherein V is one of unavoidable elements or impurities.

6. The method of any one of claims 1 to 5, wherein the preparing step comprises:

b. the ingot is homogenized at a temperature of 520 to 560 ℃ for preferably 2 to 8 hours,

and/or

c. The hot rolling of the ingot is carried out to a thickness of 3 to 10mm,

and/or

d. Cold rolling into sheets is carried out to a thickness of 1 to 4mm,

and/or

e. The solution heat treatment temperature is 540 to 580 ℃, preferably 1 second to 5 minutes,

and/or

f. The pre-ageing is carried out at a temperature of preferably 50 ℃ to 120 ℃ for at least 8 hours, preferably by coiling the sheet at a coiling temperature of 50 ℃ to 120 ℃,

and/or

g. Natural aging is at ambient temperature, preferably 72 hours to 6 months.

7. Method according to any one of claims 1 to 6, characterized in that the casting step a is a vertical semi-continuous casting step.

8. The method according to claim 6 or 7, wherein the pre-ageing is obtained by coiling the sheet at a coiling temperature of 70 ℃ to 95 ℃ and not including 95 ℃.

9. The method according to claim 6 or 7, wherein the pre-ageing is obtained by coiling the sheet at a coiling temperature of 50 to 70 ℃.

10. The method according to claim 6 or 7, wherein the pre-ageing is obtained by coiling the sheet at a coiling temperature higher than 95 ℃ and preferably from 95 to 105 ℃.

11. A rolled product obtainable by the method according to any one of claims 1 to 10.

12. A rolled product according to claim 11 obtainable by the method of claim 8 or 9, wherein the tensile yield strength of the rolled product in the T4 temper is less than 165MPa, and wherein the tensile yield strength of the rolled product in the T6B temper is at least 345 MPa.

13. A rolled product according to claim 11 obtainable by the process of claim 9, wherein the tensile yield strength of the rolled product in the T8A temper is at least 275 MPa.

14. Rolled product according to claim 11 obtainable by the method according to claim 10, wherein the difference in tensile yield strength of the rolled products of the T8C and T8D temper and made from the same rolled product of the T4 temper is less than 5MPa, and wherein the difference in tensile yield strength of the rolled products of the T6C and T6D temper and made from the same rolled product of the T4 temper is less than 5MPa, and/or wherein the maximum tensile yield strength of the rolled product of the T4 temper is 190MPa, and/or wherein the minimum tensile yield strength of the rolled product of the T6B temper is 340MPa, and/or wherein the minimum tensile yield strength of the rolled product of the T8A temper is 280MPa, preferably 290 MPa.

15. The method according to any one of claims 1 to 10, comprising the further successive steps of:

g. the rolled product is shaped into a shape, in particular by stamping,

h. optionally artificially ageing said shape,

i. the shapes are painted and "bake-hardened" into parts at a temperature of 150 ℃ to 190 ℃ and preferably 170 ℃ to 190 ℃ in 5 to 30 minutes, preferably 15 to 30 minutes.

16. Component obtainable by the method according to claim 15.

17. Use of a component according to claim 16 in an automobile as: as body skin components (or exterior body panels), for example front wings, roofs, hoods, trunks or door skins, and lining components or body structural components, for example doors, hoods, tailgates or roof linings or reinforcements, or preferably spars, bulkheads, load-bearing floors, bushings and front, middle and rear pillars, and finally impact absorbers or "crash boxes".