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
• • 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
  • C22F1/05—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 of the Al-Si-Mg type, i.e. containing silicon and magnesium in approximately equal proportions
• • 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
  • C22F1/057—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 copper as the next major constituent

Definitions

• This invention relates to a heat treatment process for shaped articles, particularly those suitable for use in the fabrication of automotive body panels More particularly, the invention relates to such articles made from aluminum alloy sheet material that exhibits an improvement of hardness after painting and baking operations have been carried out BACKGROUND ART
• Aluminum alloy sheet is being used more extensively nowadays as a structural and closure sheet material for vehicle bodies as automobile manufacturers strive for improved fuel economy by reducing vehicle weight Traditionally, aluminum alloy is either direct chill cast to form ingots or continuous cast in the form of a thick strip material, and then hot rolled to a preliminary thickness In a separate operation, the strip is cold rolled to the final thickness and wound into coil The coil must then undergo solution heat treatment to allow strengthening of the formed panel during painting and baking (steps usually carried out on shaped automotive parts by vehicle manufacturers or others - also referred to as the paint bake or paint cure)
• An object of the invention is to provide a process of producing a shaped article of enhanced hardness response without modification of a conventional procedure for produced aluminum sheet material in T4 or T4P temper
• a process of producing a painted shaped article comprising obtaining a sheet article made of an aluminum alloy of the 2000 or 6000 series in a T4 or T4P temper, shaping the article to form a shaped article, subjecting the shaped article to a thermal spiking treatment involving heating the shaped article temporarily to a peak temperature in a range of 150 to 300°C, applying paint to the article to form a painted shaped article, and, if necessary to further enhance hardness of the painted shaped article and/or to cure the applied paint, baking the article at a temperature of at least about 177°C
• thermal spike treatment means a step in which the article is quickly raised in temperature from ambient (or other temperature at which the sheet material may be heated on the part treatment line) to a predetermined maximum temperature and is then quickly cooled or allowed to cool with or without providing a holding period at the peak temperature
• shaped article includes any article obtained from sheet material for use in fabricating an article or component
• the term may include a flat article simply cut from the sheet material, but often refers to a non-planar article produced by a bending or stamping step, e g for the production of an automobile fender or door
• the term does not include unformed or uncut sheet material of indefinite length, e g coiled sheet produced directly from ingots or cast strip
• the present invention may be carried out with any precipitation hardening aluminum alloy of the AA2000 or AA6000 series, i e alloys containing Al-Mg-Si or Al- Mg-Si-Cu that are capable of exhibiting an age hardening response
• the invention also relates to a painted and shaped sheet article produced by the above process
• thermally spiked sheet material parts e g automotive panels
• the maximum hardness response in the formed part can be obtained through a thermal spiking alone without relying on the paint cure process (or without providing a paint cure at all)
• thermal spiking process at least in some forms of the invention, can be performed on a continuous basis in ovens typically used for paint cure processes
• the process therefore may be integrated seamlessly into the conventional shaping and finishing processes of parts formation, thus leading to convenience, efficiency and economy
• Figure 1 is graph illustrating a typical thermal spike treatment in accordance with the invention
• Fig 2 is a graph as explained in the Examples below, showing the variation in yield strength (YS) of conventional AA61 1 1-T4 with (a) prestrain, and (b) prestrain plus V 2 hour at 177°C, and
• Fig 3 is a graph as explained in the Examples below, showing the variation in yield strength (YS) of conventional AA61 1 1 , heat treated according to one form of the present invention, with (a) prestrain, and (b) prestrain plus Vi hour at 177°C BEST MODES FOR CARRYING OUT THE INVENTION
• an article created from the sheet is subjected to a thermal spike treatment at a temperature in the range of 150-300°C after shaping (e.g. cutting/forming/stamping)
• the treatment may either involve a thermal spike confined to the lower part of the temperature range (e.g. 150-225°C), which then relies on hardening from a subsequent paint bake step, or may involve a thermal spike into the upper part of the temperature range (e g.
• thermal spiking to temperatures in the lower part of the range may be carried out at relatively slow heating rates (e g about 1 to 70°C/minute), especially if the article is not held at the peak temperature for any time and is merely allowed to cool (or is forcefully cooled) as soon as the peak temperature is achieved
• relatively slow heating rate is often found to be necessary to improve the subsequent paint bake response, i e the desired improvement in hardness will often not materialize if the heating rate is any higher
• the heating to the peak temperature in this form of the invention may take too long for the step to be incorporated into a continuous stamping and painting line A batch treatment is therefore required.
• the heating rate may be quite rapid (e.g. 10 to 280°C/minute), even if there is essentially no holding time at the peak temperature It is found that the desired increase in hardness will occur whether the heating rate is in the lower part or the higher part of the range indicated above, but for the process to be incorporated into a continuous stamping and painting/rjaking line, the peak metal temperature (PMT) must generally be reached within about one minute If the lowest ambient temperature likely to be encountered is 15°C, the effective range for a continuous operation would likely be 210 to 285°C/minute, which is the preferred heating rate for the high temperature thermal spiking treatment
• the period of time for which the temperature is maintained at the peak thermal spike temperature may range from zero to any time that is practical in the circumstances From the metallurgical point of view, the longer the time at which the temperature is maintained, the better it is for achieving a desirable hardness response In practice the period is usually from zero up to about 5 minutes
• Fig 1 is a graphic representation of a preferred thermal spiking step showing the preferred PMT range, the overall heating rate range and the preferred time range at PMT
• the invention is illustrated by the following Examples, which are not intended to be limiting
• the invention was tested using a commercially produced AA61 1 1 material DC ingot 600 x 1600 mm double length of the AA61 1 1 alloy containing 0 72% Cu, 0 7% Mg, 0 6% Si, 0 25% Fe, 0 20% Mn and 0 06% Cr was cast on a commercial scale
• the ingots were scalped 12 5 mm per rolling face, fully homogenized, hot rolled and cold rolled to the final 0 93mm gauge, fully solutionized, rapidly cooled, naturally aged for > 48 hours and sampled for laboratory evaluation
• Figure 2 shows that the paint bake response of the AA61 1 1 -T4 material increased about 30 MPa due to aging for 30 minutes at 177°C (simulated paint cure)
• YS net yield strength
• the yield strength (YS) of the thermally spiked material decreases about 40 MPa for all levels of pre-strain, although the paint bake response is about 90 MPa, which is greater than their conventional counterparts (compare Figures 2 and 3)
• the 10% pre-strained material shows slightly less paint bake response, which is related to the loss of strength due to recovery
• the inventive process improves the paint bake response of the material, with and without prior pre-strain, quite considerably This means that the process can be used to heat-treat the formed part according to the invention and enhanced paint cure strength could be achieved EXAMPLE 2

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• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Physics & Mathematics (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Heat Treatments In General, Especially Conveying And Cooling (AREA)
• Tunnel Furnaces (AREA)
• Press Drives And Press Lines (AREA)
• Forging (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=22463077

Family Applications (1)

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Cited By (2)

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• 2000
  • 2000-05-11 EP EP00929167A patent/EP1190109B1/de not_active Expired - Lifetime
  • 2000-05-11 WO PCT/CA2000/000558 patent/WO2000070115A1/en active IP Right Grant
  • 2000-05-11 CA CA002372736A patent/CA2372736A1/en not_active Abandoned
  • 2000-05-11 JP JP2000618518A patent/JP2002544392A/ja active Pending
  • 2000-05-11 AT AT00929167T patent/ATE254673T1/de not_active IP Right Cessation
  • 2000-05-11 BR BR0010547-3A patent/BR0010547A/pt not_active Application Discontinuation
  • 2000-05-11 ES ES00929167T patent/ES2209879T3/es not_active Expired - Lifetime
  • 2000-05-11 DE DE60006670T patent/DE60006670T2/de not_active Expired - Fee Related
• 2001
  • 2001-11-09 NO NO20015497A patent/NO20015497L/no not_active Application Discontinuation

Non-Patent Citations (1)

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