Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/04—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings of inorganic non-metallic material
  • C23C28/044—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings of inorganic non-metallic material coatings specially adapted for cutting tools or wear applications
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/68—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous solutions with pH between 6 and 8
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/78—Pretreatment of the material to be coated
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D

Definitions

• the present invention relates to an aluminum alloy sheets for auto, particularly auto body panels, and to a method of manufacturing the same.
• an aluminum material having a specific gravity about one-third the specific gravity of iron has come to be used widely in place of the conventional material of steel.
• the aluminum material which is light in weight, is excellent in its corrosion resistance, formability and capability of surface treatment.
• the aluminum material can be reproduced without difficulty.
• the aluminum material attracts attentions as one of the most desirable materials for auto.
• the aluminum material is widely used nowadays for forming an auto body, a wheel, a bumper, a heat exchanger, an engine, etc. of an auto, and the range of application of the aluminum material is being widened in the field of auto.
• the alloy sheets are required to be satisfactory in, for example, formability, weldability, adhesive properties, and corrosion resistance and surface appearance after coatings.
• the auto body panels are manufactured as follows, which is substantially equal to the conventional method using steel sheets:
• a coiled aluminum alloy sheet or an aluminum alloy sheets cut into a desired size from a coiled body is formed in a desired shape.
• the aluminum alloy sheets used as a raw material are prepared by the ordinary steps of casting, soaking, hot rolling, cold rolling and finish annealing. The annealing is performed during the cold rolling step in some cases.
• the alloy sheets thus prepared are coiled or cut into a predetermined size and, then, subjected to forming.
• the aluminum alloy sheets for auto body panels prepared by the conventional method described above gives rise to serious problems.
• the aluminum alloy sheets prepared by the conventional method leaves room for further improvement in formability, compared with a steel material mainly used nowadays as a material of an auto body.
• problems such as cracking and surface roughening take place, with the result that the members of the auto body, which can be formed by using the aluminum alloy sheets prepared by the conventional method, are much restricted.
• a second problem is that the aluminum alloy sheets prepared by the conventional method are not satisfactory in its bonding strength with another member. If aluminum alloy sheets having a bonded portion is subjected to a durability test under severe conditions, peeling takes place in the bonded portion, or the bonded portion fails to exhibit a desired bonding strength. It follows that the aluminum alloy sheets prepared by the conventional method leave room for further improvement in safety and reliability.
• a third problem is that the conventional aluminum alloy sheets are not satisfactory in weldability. Because of the poor weldability, the welding apparatus, particularly the electrodes included in the apparatus, is readily damaged when alloy sheets are welded to each other. It follows that the welding apparatus, particularly the electrodes included in the apparatus, must be repaired frequently, leading to a low productivity.
• a fourth problem is that the conventional aluminum alloy sheets are not satisfactory in its bonding strength with a coated film. If a durability test is applied under severe conditions to the alloy sheets after the coating step, the coated film tends to peel off or to be swollen so as to impair the surface appearance of the alloy sheets.
• a fifth problem is that the conventional aluminum alloy sheets are poor in its corrosion resistance. If a durability test is applied under severe conditions to the alloy sheets after the coating, a filiform corrosion is brought about to impair the surface appearance of the alloy sheets. If the filiform corrosion further proceeds, the performance of the alloy sheets are lowered.
• An aluminum material is used singly for forming an auto body in some cases or is used in combination with a steel material in other cases.
• the auto body material is treated with zinc phosphate in many cases before the under coating step.
• the poor bonding strength with the coated film and the poor corrosion resistance inherent in the conventional aluminum alloy sheets are related particularly to the chemical conversion treatment with zinc phosphate.
• an oxide film formed on the surface of an aluminum alloy sheets It has also been found that the structure of an oxide film of aluminum is greatly affected by the composition of the aluminum alloy.
• an aluminum alloy sheets used for forming an auto body contains 0.3 to 10% by weight of magnesium.
• the oxide film formed on the surface of such an alloy sheets contains not only aluminum oxide and/or hydroxide but also magnesium oxide and/or hydroxide. It has been found that the weldability, bonding strength and corrosion resistance of the alloy sheets are adversely affected by the presence of magnesium oxide and/or hydroxide noted above.
• the aluminum oxide can be roughly classified into two types, i.e., amorphous oxide (Al2O3) and crystalline oxide.
• the crystalline aluminum oxide film is in the form of various phases depending on the atmospheres under which the oxide film is formed.
• the typical phases of the crystalline aluminum oxide include, for example, Gibbsite ( ⁇ -Al(OH)3), Bayerlite ( ⁇ -Al(OH)3), and Boehmite ( ⁇ -AlOOH).
• the crystalline aluminum oxide film exhibits a frictional resistance lower than that of the amorphous aluminum oxide film and, thus, is superior to the amorphous oxide film in lubricity. It should be noted that these two kinds of oxides are present together in the oxide film formed on the surface of the aluminum alloy sheets after the rolling step. Also, the crystalline oxide is formed when the alloy sheets is exposed to a wet atmosphere of high temperatures.
• a crystalline oxide film is formed in the hot rolling step in the manufacture of an aluminum alloy sheets.
• an aqueous rolling oil of 200°C or more is used in the hot rolling step, which is considered to give rise to formation of the crystalline oxide film.
• the crystalline oxide film is broken in the subsequent cold rolling step.
• crystalline oxide is embedded in the aluminum matrix so as to remain within the product alloy sheet.
• the present inventors have also found that the weldability, adhesive properties, and corrosion resistance of an aluminum alloy sheets are affected by the presence of two kinds of oxides, i.e., aluminum oxide and magnesium oxide, contained in the oxide film formed on the surface of the aluminum alloy sheets. Particularly, it has been found that these properties of the alloy sheets are markedly deteriorated in the case where the oxide film contains a large amount of magnesium oxide.
• An object of the present invention is to remove magnesium oxide contained in an oxide film formed on the surface of an aluminum alloy sheets as much as possible to improve the properties of the alloy sheets and to prevent formation of magnesium oxide even if the alloy sheets having the magnesium oxide removing treatment applied thereto is left to stand for a long period of time, so as to provide aluminum alloy sheets which permits suppressing the change with time in the properties and is suitable for forming auto body panels.
• aluminum alloy sheets for auto bodies comprising a metal aluminum substrate formed of an aluminum alloy containing 2 to 10% by weight of magnesium; an aluminum phosphate film formed on the substrate; an aluminum oxide film formed on the phosphate film; and, as desired, an oil film formed on the aluminum oxide film.
• Another object of the present invention is to provide a method of efficiently manufacturing aluminum alloy sheets which permits suppressing the change with time in the properties and is suitable for forming auto bodies.
• a method of manufacturing aluminum alloy sheets for auto bodies comprising the steps of: treating the surface of aluminum alloy sheets containing 2 to 10% by weight of magnesium with an acid having a pH value of at most 4 to remove magnesium oxide contained in an aluminum oxide-based film formed on the surface of the alloy sheets; treating the surface of the alloy sheets with a phosphate solution to form an aluminum phosphate film between the metal aluminum substrate and the aluminum oxide film; and, as desired, coating the aluminum oxide film with an oil to form an oil film.
• An aluminum alloy containing 2 to 10% by weight of magnesium is used in the present invention including, for example, JIS A5052 alloy, JIS A5182 alloy, JIS A5082 alloy, JIS A5083 alloy, JIS A5086 alloy, and Al(8 wt%)-Mg alloy. It is important for the magnesium content of the aluminum alloy to fall within a range of between 2 and 10% by weight. If the magnesium content is lower than 2% by weight, the alloy fails to exhibit a sufficiently high mechanical strength. If the magnesium content is higher than 10%, however, it is difficult to prepare an aluminum alloy sheets.
• magnesium oxide and magnesium oxide are contained in an oxide film formed on the surface of the aluminum alloy sheets manufactured by the ordinary method.
• magnesium oxide alone is selectively removed in the first step by a treatment with an acid from among the mixture of aluminum oxide and magnesium oxide which are originally present on the metal aluminum substrate consisting of aluminum alloy sheets.
• the pH value of the acid used for this treatment is set at at most 4. If the pH value is 4 or less, the acid permits selectively dissolving magnesium oxide alone on the substrate surface without dissolving the substrate metal of aluminum and aluminum oxide on the substrate surface. It follows that it is possible to allow the crystalline aluminum oxide having a high lubricity, which is formed in the hot rolling step, to be left unremoved.
• the acids which can be used in the present invention include, for example, 0.5 to 30 wt% nitric acid and 0.5 to 30 wt% sulfuric acid.
• magnesium oxide such that the amount of magnesium oxide is made at most 20% by weight based on the total amount of the oxides formed on the metal substrate surface. If the amount of magnesium oxide is larger than 20% by weight based on the total amount of the oxides, the magnesium oxide film itself acts as a brittle layer (peeling portion) in the bonding step of the sheets to another member, leading to a low bonding strength. Also, an electrical resistance is increased in the welding step so as to impair the electrodes of the welding apparatus. As a result, the fused portion called nugget is diminished during the continuous welding operation, resulting in failure to obtain a desired mechanical strength.
• the aluminum oxide originally present on the substrate surface mainly remains on the metal substrate consisting of the aluminum alloy sheets. It is desirable for the aluminum oxide film to have a thickness falling within a range of between 10 and 200 ⁇ . If the aluminum oxide film has a thickness smaller than 10 ⁇ , the electrical resistance of the substrate is unduly low in the spot welding step, resulting in failure to obtain a sufficient heat generation. Thus, nuggets are not formed. If the thickness exceeds 200 ⁇ , however, the aluminum oxide film itself acts as a brittle layer in the bonding step, leading to a low bonding strength. Further, the electrical resistance is too much increased in the spot welding step, with the result that the electrodes of the welding apparatus are impaired so as to decrease the number of continuous welding points achieved by using the same welding apparatus.
• the aluminum oxide film prefferably has an average surface roughness Ra falling within a range of between 0.1 and 2.5 microns and a maximum surface roughness Rmax falling within a range of between 0.5 and 40 microns. If the average surface roughness Ra is less than 0.1 micron and the maximum surface roughness Rmax is less than 0.5 micron, it is difficult to hold sufficiently a lubricating oil supplied to the aluminum alloy sheets in the forming step, leading to a low formability of the sheet. Further, the aluminum alloy sheet is rendered low in its adhesive properties because the low surface roughness denotes a small bonding area.
• the surface of the coated film after the coating step is rendered poor in its smoothness and appearance so as to decrease the commercial value of the alloy sheets.
• the substrate having magnesium oxide removed from the surface thereof by the acid treatment is then treated with a phosphate solution so as to form a phosphate film between the metal substrate of the aluminum alloy sheets and the aluminum oxide film.
• the thickness of the aluminum phosphate film should be about 1 to 5 ⁇ . Incidentally, a sufficient effect can be obtained by the presence of the aluminum phosphate film even if the phosphate film is in the form of a monomolecular film.
• the thickness of the aluminum phosphate film can be controlled by adjusting appropriately the conditions such that the concentration of the phosphate solution falls within a range of between 0.01 and 5% by weight, the temperature of the phosphate solution is 20°C or more, and the treating time is at least 2 seconds.
• a solution containing phosphate ions can be used for forming the aluminum phosphate film including, for example, a solution containing at least 0.01% by weight of at least one of sodium phosphate, sodium phosphite and sodium pyrophosphate.
• the treatment with a phosphate solution makes it possible to prevent formation of magnesium oxide even if the aluminum alloy sheet is allowed to stand over a long period of time. As a result, the change with time in the properties of the aluminum alloy sheet can be suppressed.
• the aluminum oxide film originally formed on the surface of the substrate is porous.
• the phosphate solution passes through the aluminum oxide film during treatment with the phosphate solution to perform a chemical reaction with the substrate aluminum to form a strong aluminum phosphate film between the metal aluminum substrate and the aluminum oxide film.
• the oil coating further promotes the effect of suppressing the magnesium oxide formation.
• the oil used in the present invention includes, for example, an antirust oil in the form of emulsion or wax. Concerning the coating amount of oil, a sufficient effect can be expected as far as the entire surface region is uniformly coated with the oil. In practice, the oil is coated in an amount of at least 0.1 g/m2, preferably about 1 g/m2.
• a coil of the raw material alloy sheets is cut into sheets of a predetermined size, followed by applying each of the treatments described above to the cut sheets.
• each of the treatments can be continuously applied to a coiled raw material alloy sheets.
• the continuous treatment permits manufacturing aluminum alloy sheets with an improved efficiency and with a high productivity.
• An ingot was prepared by melting and casting JIS A5182 alloy (Al 0.3 wt%-Mn 4.5 wt%-Mg alloy), followed by applying successively a homogenizing treatment, a hot rolling treatment, a cold rolling treatment, and finish annealing treatment to the ingot so as to obtain a sheets having a thickness of 1.0 mm.
• the resultant sheets was treated with a 5 wt% nitric acid for 10 seconds by a spraying method, followed by washing the sheets with water so as to remove selectively magnesium oxide contained in an oxide film formed on the surface of the sheets. Then, the washed sheets was dried.
• the sheets was treated with a 0.1 wt% sodium pyrophosphate solution at 40°C for 300 seconds to form an aluminum phosphate film having a thickness of 5 ⁇ between the metal aluminum substrate and the aluminum oxide film formed on the substrate, thereby to obtain an aluminum alloy sheet 1 of the present invention.
• various properties of the aluminum sheet 1 were measured, including the total thickness of the oxide film (sum of the magnesium oxide film and the aluminum oxide film), the percentage by weight of the magnesium oxide film based on the sum of the magnesium oxide film and the aluminum oxide film, the formability, adhesive properties, weldability, bonding strength with a coated film, and corrosion resistance. Table 1 shows the results. These properties were also measured after the aluminum alloy sheet 1 was left to stand for 90 days within a constant temperature-humidity bath maintained at a temperature of 40°C and a relative humidity of 95% so as to evaluate the changes with time in these properties. Table 1 also shows the results. The properties noted above were evaluated as follows:
• Erichsen test A defined in JIS Z2247 was applied applied to the aluminum alloy sheets 1 to determine the Erichsen value (mm) as the formability.
• a small sheets sized at 70 mm ⁇ 150 mm was cut out of the aluminum alloy sheets 1 of the present invention and, then, subjected to a degreasing treatment at 45°C for 30 seconds using a weakly alkaline degreasing agent.
• the surface of the sample was adjusted at room temperature for 30 seconds with a colloidal titanium-based liquid material, followed by applying a chemical treatment to the sample under the surface-adjusted state with a zinc phosphate solution available on the market.
• the chemical conversion treatment was performed for 2 minutes at 45°C.
• the sample was successively subjected to rinsing with water, drying, under coating with a cation electrolyte deposition, intermediate coating by blowing, and top coating.
• the resultant sample was kept immersed in warm water of 50°C for 20 days, followed by applying a cross cut adhesion test. Specifically, a peeling test using a tape was applied to the sample in the form of a checkerboard having 100 meshes each sized 2 mm ⁇ 2 mm. The number of residual meshes which were not peeled off was indicated in Table 1 together with the number of test pieces (100).
• a sample was prepared as in the bonding strength test with a coated film. Then, a cross-cut (i.e., a mark X) was applied to the surface of the sample such that the cross-cut reached the aluminum alloy sheet. Under this condition, a salt water spraying test specified in JIS Z2371 was applied to the sample for 24 hours, followed by allowing the sample to stand in a wet atmosphere for 2,000 hours at a temperature of 50°C and a relative humidity of 95% so as to measure the maximum length of a filiform corrosion extending from the cross-cut portion.
• a cross-cut i.e., a mark X
• An aluminum alloy sheets 2 of the present invention was obtained substantially as in Example 1, except that an aluminum phosphate film having a thickness of 2 ⁇ was formed in Example 2 between the metal aluminum substrate and the aluminum oxide film by the treatment with a 0.05 wt% sodium phosphate solution for 10 seconds at 90°C, though an aluminum phosphate film having a thickness of 5 ⁇ was formed in Example 1 by the treatment with a 0.1 wt% sodium pyrophosphate solution for 300 seconds at 40°C.
• Example 1 Various properties of the aluminum alloy sheets 2 were measured as in Example 1, including the total thickness of the oxide film, the percentage by weight of the magnesium oxide film based on the sum of the magnesium oxide film and the aluminum oxide film, the formability, adhesive property, weldability, bonding strength with a coated film, and corrosion resistance. Table 1 also shows the results together with the changes with time in these properties.
• An aluminum alloy sheets 3 of the present invention was obtained substantially as in Example 1, except that an aluminum phosphate film having a thickness of 5 ⁇ was formed in Example 3 between the metal aluminum substrate and the titanium oxide film by the treatment with a 3 wt% sodium pyrophosphate solution for 120 seconds at 50°C, though an aluminum phosphate film having a thickness of 5 ⁇ was formed in Example 1 by the treatment with a 0.1 wt% sodium pyrophosphate solution for 300 seconds at 40°C. Further, the aluminum oxide film (the uppermost film) was coated with an emulsion type antirust oil having a viscosity of 3 cSt in a coating amount of 1 g/m2 in Example 3.
• Example 1 Various properties of the aluminum alloy sheets 3 were measured as in Example 1, including the total thickness of the oxide film, the percentage by weight of the magnesium oxide film based on the sum of the magnesium oxide film and the aluminum oxide film, the formability, adhesive property, weldability, bonding strength with a coated film, and corrosion resistance. Table 1 also shows the results together with the changes with time in these properties.
• An ingot was prepared by melting and casting JIS A5182 alloy, followed by applying successively a homogenizing treatment, a hot rolling treatment, a cold rolling treatment, and finish annealing treatment to the ingot so as to obtain a sheets having a thickness of 1.0 mm.
• the resultant sheets was treated with a 5 wt% nitric acid for 10 seconds by a spraying method, followed by rinsing the sheets with water so as to remove selectively magnesium oxide contained in an oxide film formed on the surface of the sheets. Then, the rinsed sheets was dried.
• the residual aluminum oxide film was coated with an emulsion type antirust oil having a viscosity of 5 cSt in an amount of 1 g/m2 so as to obtain an aluminum alloy sheets (prior art 1).
• Example 1 Various properties of the aluminum alloy sheets (prior art 1) were measured as in Example 1, including the total thickness of the oxide film, the percentage by weight of the magnesium oxide film based on the sum of the magnesium oxide film and the aluminum oxide film, the formability, adhesive property, weldability, bonding strength with a coated film, and corrosion resistance. Table 1 also shows the results together with the changes with time in these properties.
• An aluminum alloy sheets (prior art 2) was prepared as in prior art 1, except that a wax-type antirust oil was in place of the emulsion type antirust oil having a viscosity of 5 cSt, which was used in Prior Art 1.
• Example 2 Various properties of the aluminum alloy sheets (prior art 2) were measured as in Example 1, including the total thickness of the oxide film, the percentage by weight of the magnesium oxide film based on the sum of the magnesium oxide film and the aluminum oxide film, the formability, adhesive property, weldability, bonding strength with a coated film, and corrosion resistance. Table 1 also shows the results together with the changes with time in these properties.
• An ingot was prepared by melting and casting JIS A5182 alloy, followed by applying successively a homogenizing treatment, a hot rolling treatment, a cold rolling treatment, and finish annealing treatment to the ingot so as to obtain a sheets having a thickness of 1.0 mm.
• the resultant sheets was treated with a 5 wt% nitric acid for 10 seconds by a spraying method, followed by washing the sheets with water so as to remove selectively magnesium oxide contained in an oxide film formed on the surface of the sheets. Then, the washed sheets was dried so as to obtain an aluminum alloy sheets (prior art 3).
• Example 3 Various properties of the aluminum alloy sheets (prior art 3) were measured as in Example 1, including the total thickness of the oxide film, the percentage by weight of the magnesium oxide film based on the sum of the magnesium oxide film and the aluminum oxide film, the formability, adhesive property, weldability, bonding strength with a coated film, and corrosion resistance. Table 1 also shows the results together with the changes with time in these properties.
• the aluminum alloy sheets of the present invention is small in the changes with time in properties.
• the thickness of the oxide film was increased in the prior art aluminum alloy sheets after the sheets was allowed to stand in a humid atmosphere of a high temperature for a long time.
• the properties of the aluminum alloy sheets were greatly changed with time in the prior art.
• the present invention provides aluminum alloy sheets for auto body panels.
• magnesium oxide is removed from the natural oxide film formed on the surface of the alloy sheets, followed by forming an aluminum phosphate film between the metal aluminum substrate and the aluminum oxide film. Further, an oil film is formed as required on the uppermost layer of the aluminum oxide film.
• the particular construction of the present invention makes it possible to improve the characteristics including the formability, adhesive property, and weldability of the aluminum alloy sheets.
• formation of magnesium oxide can be markedly suppressed over a long period after manufacture of the alloy sheets.
• the aluminum alloy sheets of the present invention permits suppressing the changes with time in the characteristics thereof.
• the aluminum alloy sheets for auto bodies provided by the present invention permits promoting the forming rate of a chemical conversion film during the chemical treatment in the coating step so as to suppress the elusion of aluminum ions into the coating solution.
• a chemical conversion film can be formed uniformly on the aluminum alloy sheet, leading to a high bonding strength of the alloy sheets with a coating film and to a high corrosion resistance of the alloy sheets.
• the present invention also provides a method of manufacturing an aluminum alloy sheets for auto bodies, which makes it possible to manufacture efficiently an aluminum alloy sheets which permits suppressing the changes with time in the characteristics of the alloy sheets.

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• General Chemical & Material Sciences (AREA)
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• 1992
  • 1992-09-04 CA CA002095525A patent/CA2095525A1/en not_active Abandoned
  • 1992-09-04 KR KR1019930701343A patent/KR960004783B1/ko not_active IP Right Cessation
  • 1992-09-04 WO PCT/JP1992/001131 patent/WO1993005199A1/ja not_active Application Discontinuation
  • 1992-09-04 EP EP92918876A patent/EP0557531A1/en not_active Withdrawn

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