Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/043—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with silicon as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent

Definitions

• the invention relates to the domain of Al-Si-Mg alloy sheets, more particularly made of a 6016 type alloy according to the Aluminum Association, to be used for manufacturing by drawing of car body outer panel parts such as wings, doors, tailgates, bonnets and roofs.
• Aluminium is increasingly used in automobile construction to reduce the weight of vehicles and thus reduce fuel consumption and the release of pollutants and greenhouse gases. Sheets are used particularly for making body outer panel parts, particularly doors. This type of application requires a number of properties that are sometimes contradictory, for example:
• Al-Mg-Si alloys in the 6000 series have been chosen to satisfy these requirements.
• the 6016 and 6016A alloys with thicknesses of the order of 1 to 1.2 mm are most frequently used for this application since they give a better compromise between the various required properties, particularly enabling better formability, particularly for hemming, and better resistance to filiform corrosion than alloys with a higher copper content such as the 6111 alloy that is widely used in the United States.
• 6016 type alloys are described particularly in Alusuisse's patent FR 2360684 and the applicant's patent EP 0259232, while 6111 type alloys are described in Alcan International Limited's patent U.S. Pat. No. 4,614,552.
• compositions (% by weight of the main elements) of the 6016, 6016A, 6022 and 6111 alloys registered at the Aluminum Association are indicated in table 1: TABLE 1 Alloy Si Fe Mg Cu Mn 6016 1.0-1.5 ⁇ 0.5 0.25-0.6 ⁇ 0.2 ⁇ 0.2 6016A 0.9-1.5 ⁇ 0.5 0.2-0.6 ⁇ 0.25 ⁇ 0.2 6022 0.8-1.5 0.05-0.2 0.45-0.7 0.01-0.11 0.02-0.10 6111 0.5-1.0 ⁇ 0.4 0.5-1.0 0.5-0.9 ⁇ 0.4
• the mechanical strength of the 6016 alloy after the paint has been baked, and therefore the dent resistance remains significantly lower than the corresponding values for the 6111 alloy, particularly since the baking temperature is tending to go down such that hardening during ageing is less effective. This is why automobile manufacturers are asking for a higher mechanical strength after painting.
• Alcan has proposed a new variant of the 6111 alloy called 6111-T4P, which has an improved yield strength after baking the paint (typically 270 to 280 MPa) without reducing formability in the T4 temper.
• 6111-T4P 6111-T4P
• this product has been described in the article by A. K. Gupta et al. “The Properties and Characteristics of Two New Aluminium Automotive Outer Panel Materials”, SAE Technical Paper 960164, 1996.
• the article also mentions a new alloy temporarily called 61XX-T4P, for which the composition has not been divulged, which has a lower yield strength in the T4 state than the conventional 6111-T4, with a similar response to paint baking.
• the purpose of this invention is to provide 6016 type alloy sheets for automobile body outer panels with a composition adapted to recycling, sufficient formability for deep drawing and hemming under severe conditions, improved resistance to indentation compared with sheets of the 6016 type according to the prior art while controlling springback, with good gluing properties, cutting without the formation of slivers, and good resistance to filiform corrosion.
• the subject of the invention is a sheet for an automobile body outer panel part between 0.8 and 1.2 mm thick, and the following composition (% by weight): Fe: 0.25-0.40 and preferably: 0.25-0.35 Si: 0.90-1.20 and preferably: 0.95-1.10 Cu: 0.10-0.25 and preferably: 0.15-0.20 Mg: 0.35-0.50 and preferably: 0.40-0.50 Mn: 0.05-0.20 and preferably: 0.08-0.15
• the invention is based on a narrow composition range within the definition of the 6016A composition registered at the Aluminium Association, in order to obtain all the required properties.
• the silicon content is near the bottom part of the content range of 6016A, while the magnesium content is at the centre of the range. This drop in the silicon content contributes to more complete solution heat treatment of the alloy, favourable for formability.
• the iron content remains above 0.25% which, unlike low iron grades such as 6022, enables the use of recycled metal and results in a better surface appearance after drawing.
• the copper content is controlled within very narrow limits: a content of at least 0.1%, slightly more than the content for existing 6016 or 6022 grades, contributes to the mechanical strength, but above 0.25% there is a risk of filiform corrosion of the alloy.
• the alloy must contain at least 0.05% of manganese, chromium, vanadium or zirconium to control the grain size and prevent the appearance of orange peel during severe deformations, for example such as hemming used for bonnets. Conversely, if the total content of these elements exceeds 0.20%, it is bad for formability.
• the sheet manufacturing process according to the invention typically includes casting of a plate, possibly scalping of this plate and homogenisation by simply heating it to a temperature of between 400 and 570° C. for between 6 and 24 h.
• Hot rolling preferably takes place at an input temperature of more than 510° C., which contributes to making the mechanical strength better than what would be obtained at a lower input temperature.
• the winding temperature of the hot rolled strip must be less than 350° C., and preferably 300° C., to guarantee mechanical characteristics and to avoid any ridging defects.
• the hot rolled strip is then cold rolled down to the final thickness, possibly with intermediate annealing at a temperature of between 300 and 450° C. if it is done in a batch furnace, or between 350 and 570° C. if is done continuously.
• the last cold rolling pass may be made with a textured cylinder, for example by electron beam treatment (EBT), electro-erosion (EDT), or by laser beam which improves the formability and surface appearance of the part formed after painting
• the solution heat treatment takes place at a temperature above the alloy solvus temperature while avoiding overheating.
• the composition according to the invention is capable of very complete solution heat treatment, resulting in an almost complete absence of silicon type phases in the microstructure and by a very small peak area, less than 1 J/g in the 565-580° C. range in a differential enthalpy analysis diagram, the test being carried out at a temperature rise rate of 20° C./min.
• the sheet After the solution heat treatment, the sheet is quenched, usually with cold water or air. Quenching may be followed immediately by a pre-ageing type heat treatment like that described in the prior art mentioned above, in order to improve hardening performances of the paint during baking.
• the sheet is usually stored for a variable time period at this stage, which leads to natural ageing that increases the yield strength with time.
• the thickness of sheets according to the invention is of the order of 0.9 to 1 mm
• the yield strength in the L direction is of the order of 130 MPa which is higher than all 6016 variants, including high strength grades DR100 and DR120 described in the article by R. Shahani et al. mentioned above, and only slightly lower than the value for 6022. After six months ageing, this yield strength remains below 160 MPa or even 150 MPa, unlike 6022 and 6111 alloys.
• the sheet Before forming, the sheet may be coated with a lubricant (oil or dry lubricant) adapted to drawing, assembly and surface treatment of the part to be made.
• a lubricant oil or dry lubricant
• Sheets according to the invention have formability as measured by the LDH 0 (“Limiting Dome Height” in plane deformation) parameter that is better than the 6111 and 6022 alloys and as good as high strength 6016 grades.
• LDH 0 Liting Dome Height
• the LDH parameter is broadly used for evaluating the drawability of 0.5 to 2 mm thick sheets.
• Many publications have been made, particularly the publication by R. Thomson, “The LDH test to evaluate sheet metal formability—Final Report of the LDH Committee of the North American Deep Drawing Research Group”, SAE Conference, Detroit, 1993, SAE Paper No. 930815.
• the LDH test is a drawing test on a blank blocked by a retaining ring around its periphery.
• the pressure of the blank clamp is controlled to prevent sliding in the retaining ring.
• the 120 ⁇ 160 mm blank is strengthed in a mode similar to plane deformation.
• Lubrication between the stamp and the sheet is achieved using a plastic film and grease (Shell HDM2 grease).
• the punch lowering speed is 50 mm/min.
• the LDH value is the displacement of the punch at failure, namely the drawing limiting depth. The average of three tests is determined, giving a confidence range of 95% on a measurement of ⁇ 0.2 mm.
• Sheets according to the invention have better crimpability than 6111 or 6022 alloy sheets, and the crimpability is just as good as high strength 6016 alloy sheets according to the prior art.
• This hemming ability is evaluated by a laboratory test including flanging at 90°, pre-hemming at 45° and final flat hemming.
• Sheets according to the invention also have a very small deformation anisotropy that can be measured by the difference between the LDH for a principal deformation parallel to the rolling direction, and a principal deformation perpendicular to the rolling direction. This difference is less than 1 mm and preferably less than 0.6 mm.
• the body outer panel part is usually made by cutting out a blank in the sheet, drawing this blank and trimming it with the press.
• stamping it is essential to avoid the occurrence of roping or ridging, which deteriorates the final paint appearance and can reduce formability, particularly in the case of severe deformation in the direction perpendicular to the rolling direction.
• Different means have been provided for this purpose, for example controlling the hot rolling outlet temperature between 270 and 340° C., as indicated in the applicant's patent EP 0259232. It is also important to avoid the occurrence of “orange peel” stamping which contributes to a visible appearance defect after painting.
• the grain size smaller than 50 ⁇ m, which can be achieved by the presence of a sufficient quantity of manganese in the alloy, or other elements playing a similar role such as chromium, vanadium or zirconium, by temperature control and by the time of the solution heat treatment and by a sufficient reduction, typically at least 30% by cold rolling.
• the edges of the drawn blank are flanged at 90° and a lining stamping is inserted on which pre-hemming is done followed by final flat hemming.
• the part After stamping and possibly hemming, the part is covered by one or more coats of paint, with a baking step following each coat.
• the critical step is baking of the cataphoresis layer, which is usually done at a temperature of between 150 and 200° C. for 15 to 30 minutes. The baking temperature rarely exceeds 170° C. if there is no cataphoresis. Paint baking contributes towards an ageing treatment of the part.
• the yield strength of the part made with a sheet according to the invention, with baking for 20 minutes at 165° C., is higher than 180 MPa and often higher than 200 MPa.
• the resistance to dynamic indentation is similar to the value for a part made from a typical body steel sheet with a yield strength of the order of 250 to 300 MPa and 0.7 mm thick, which is not the case for other 6016 grades.
• Sheets according to the invention can be used to perform different operations routinely performed for making car body outer panel parts, such as hemming, clinching, riveting, spot welding, laser welding and gluing.
• Parts made from sheets according to the invention also have good resistance to filiform corrosion after painting, better than alloys with a high copper content like 6111 alloy.
• the major difficulty is with the management of differences in thermal expansion between two materials when the paint is being baked, particularly during the cataphoresis baking which is usually done at between 160 and 200° C. It is essential to limit residual deformations after baking to a level acceptable for the appearance of the vehicle.
• Sheets according to the invention can limit these deformations, independently of the geometry of the parts and the assembly mode chosen.
• the applicant thus demonstrated that a high yield strength at the baking temperature, for example more than 140 MPa at a temperature of 160° C. for the alloy according to the invention, had a favourable effect on the deformation level, if the assembly is made after baking, and it is thus preferable to limit the baking temperature.
• Composition A represents a conventional 6016 alloy
• B is the applicant's grade DR100 described in the articles mentioned above
• C and D are a 6111 alloy
• E is a 6022 alloy
• F, G, H and I are alloys with similar compositions, differing either by Cu (F), or by Mn (G and H) from the composition I according to the invention.
• the plates were scalped and homogenised for 10 h at 570° C., and then hot rolled directly on homogenisation heat, firstly on a reversible mill, then on a tandem mill.
• the lamination start temperature was of the order of 540° C.
• the hot strip winding temperature was of the order of 310° C.
• the hot rolled strip rolled to 3 mm is then cold rolled to the final thickness of 1 mm.
• An intermediate annealing is carried to a thickness of 2.5 mm, consisting of either a “batch” annealing in a coil with a temperature rise to 350° C. in 10 h, 2 h waiting time followed by slow cooling, or a “flash” annealing in a continuous furnace with a temperature rise to 400° C. in about one minute and immediate cooling.
• Samples taken from the strips are subjected to a solution heat treatment at a temperature of 570° C. for less than one minute, and are then quenched in cold water.
• Complementary treatment for 2 h at 100° C. in the oil bath immediately after quenching to simulate industrial pre-ageing is applied to samples made of alloys B, D, F, G, H and I.
• the yield strength R 0.2 (in MPa) was measured in the L direction after 3 weeks and 6 months ageing at ambient temperature, followed by an ageing treatment for 30 minutes at 165° C. or 185° C., simulating the paint baking treatment.
• the formability was also measured using the LDH parameter (in mm), the principal deformations being parallel to and perpendicular to the rolling direction respectively. The results are given in table 2: TABLE 2 A B C D E F G H I Inter.
• sample I according to the invention has the same order of yield strength as the conventional 6016 (sample A) and significantly lower than the corresponding value of the 6111 alloys (C and D) and the 6022 alloy (E). The position of the yield strength of sample I with respect to other alloy samples has not changed after 6 months of ageing.
• Formability as measured by the LDH parameter, is practically as good as the formability of the best alloy, which is the DR100. Moreover, measured values of LDH in the rolling direction and in the direction perpendicular to the rolling direction are practically identical, which is not always the case for other samples, which enables good isotropy in forming.
• the yield strength of sample I after the paints have been baked following a pre-ageing is high, significantly higher than the value for the 6016 and DR100 alloys, of the same order as the value for alloy F which has a higher content of copper, and is intermediate between the values for the two 6111 grades, guaranteeing high dent resistance of the finished part.
• the behaviour during hemming was also measured on 1 mm thick sheets in the direction parallel to rolling and in the direction perpendicular to rolling, the resistance to filiform corrosion after phosphating, cataphoresis and painting and the occurrence or lack of occurrence of slivers of filaments when cutting out or trimming after drawing.
• the hemming test is done in three operations: flanging of edges at 90° C., pre-hemming at 45° and hemming flat on a 0.7 mm thick lining plate. The hemmed edges are then classified by visual inspection, as described in the article by D. Daniel et al. in IBEC 99.
• the resistance to filiform corrosion is evaluated according to standard EN 3665, with sample size 150 ⁇ 60 ⁇ 1 mm after painting and scratching.
• the test procedure includes corrosion activation by HCl vapour for 1 h, followed by exposure in a wet room at 40° C. for 1000 h.
• the cut test is described in the article by D. Daniel et al in IBEC 99 mentioned above. The clearance was 10% of the thickness and the cutting angle was 0°.
• Aluminium alloy panels were made with the composition indicated in table 4, with a manufacturing procedure similar to that in example 1, possibly but not necessarily comprising pre-ageing and heat treatment after forming and before assembly, as also mentioned in table 4.
• the panel dimensions are 1.6 m ⁇ 0.9 m.
• TABLE 4 T eq Si Fe Mg Cu Mn pre- Sample Alloy (%) (%) (%) (%) (%) (%) ageing Anneal.
• Inv. 1.05 0.25 0.45 0.19 0.14 5 h No L 6111 0.70 0.25 0.60 0.69 0.21 —
• the alloy according to the invention effectively reduces residual thicknesses after baking.
• the performance of alloys is clearly correlated with the yield strength at the baking temperature.
• heat treatment before assembly and the addition of ribs are beneficial in reducing deformations.
• the device used for the indentation test comprises a 15 mm-diameter indenter weighing 138 g, released from a height of 1 m at a speed of about 16 km/h, onto the sample sheet clamped between two steel plates.
• the permanent indentation depth is measured (in mm).
• the results are given in table 6.
• R 0.2 Indent. Baking Inv R 0.2 R 0.2 Inv Indent. Indent. temperature all. DR100 steel all. DR100 steel 170° C. 193 161 290 1.55 1.80 1.45 185° C. 217 189 290 1.45 1.62 1.45 205° C. 230 207 290 1.38 1.46 1.45
• the 1 mm-thick sheet according to the invention has the same dent resistance as the 0.7-mm thick steel sheet.
• a paint baking temperature 185° C.
• 205° C. which is higher than temperatures usually used by automobile manufacturers.
• a stronger alloy such as 6111 would increase the dent resistance to exceed market needs, but this would be to the detriment of formability, particularly during hemming.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Crystallography & Structural Chemistry (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Laminated Bodies (AREA)
• Body Structure For Vehicles (AREA)
• Motor Or Generator Frames (AREA)
• Shaping Metal By Deep-Drawing, Or The Like (AREA)
• Heat Treatment Of Articles (AREA)
• Metal Rolling (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=27619894

Family Applications (1)

Country Status (11)

Cited By (23)

Families Citing this family (5)

Citations (5)

Family Cites Families (12)

• 2002
  • 2002-02-05 FR FR0201346A patent/FR2835533B1/fr not_active Expired - Fee Related
• 2003
  • 2003-02-03 WO PCT/FR2003/000318 patent/WO2003066919A2/fr active Application Filing
  • 2003-02-03 AU AU2003216971A patent/AU2003216971A1/en not_active Abandoned
  • 2003-02-03 KR KR1020047012157A patent/KR100964855B1/ko not_active IP Right Cessation
  • 2003-02-03 US US10/502,659 patent/US20050028894A1/en not_active Abandoned
  • 2003-02-03 JP JP2003566264A patent/JP2005525462A/ja active Pending
  • 2003-02-03 DE DE03712292T patent/DE03712292T1/de active Pending
  • 2003-02-03 ES ES03712292T patent/ES2316738T3/es not_active Expired - Lifetime
  • 2003-02-03 AT AT03712292T patent/ATE413476T1/de not_active IP Right Cessation
  • 2003-02-03 DE DE60324526T patent/DE60324526D1/de not_active Expired - Lifetime
  • 2003-02-03 EP EP03712292A patent/EP1472380B1/de not_active Revoked
  • 2003-02-03 CA CA2471501A patent/CA2471501C/fr not_active Expired - Fee Related
• 2008
  • 2008-12-09 JP JP2008312816A patent/JP2009133006A/ja active Pending

Patent Citations (5)

Also Published As

Similar Documents

Legal Events