US20070029207A1

US20070029207A1 - Oxide coating for enhancing metal formability

Info

Publication number: US20070029207A1
Application number: US11/198,483
Authority: US
Inventors: James Anglin; Larry Wieserman; Al Askin; John Bohaychick
Original assignee: Alcoa Inc
Current assignee: Howmet Aerospace Inc
Priority date: 2005-08-05
Filing date: 2005-08-05
Publication date: 2007-02-08
Also published as: WO2007019235A2; WO2007019235A3

Abstract

This invention discloses a metal product that is suitable for a forming process. By anodizing an oxide layer onto at least one surface of the metal product, the total amount of lubricant that is applied onto the metal product prior to being formed is reduced or eliminated. This invention also discloses a method of generating such an oxide layer onto the metal product.

Description

FIELD OF THE INVENTION

This invention relates generally to metal forming. More specifically, this invention discloses a method in which an enhanced oxide layer is generated on an aluminum alloy to reduce or eliminate the total amount of lubricant that is applied to the aluminum alloy prior to the metal forming process.

BACKGROUND OF THE INVENTION

Metal forming, in most instances, is performed with the aid of lubricants in order to control the friction that is generated between the forming tool and the surface of the metal workpiece during the forming process, and to limit or eliminate the transfer of metal from the metal workpiece to the tooling surface. Most metals, including aluminum and its alloys, which are used in a forming process have a natural oxide layer that is present on the surface of the metal. The natural oxide layer's formation is due to a reaction between the metal's surface and the oxygen, water, and other oxidizing species in the environment. Under dry conditions at room temperature, the oxide layer that naturally forms on the surface of an aluminum object has thickness ranging from about 2.5 nm to about 3.0 nm. Metal transfer tends to occur when the contact conditions during a forming process are severe enough to substantially disrupt the naturally formed oxide layer that is present on the surface of the metal workpiece. Some lubricants, however, can minimize the occurrence of metal transfer even under these severe forming conditions. Additionally, some lubricants can also facilitate the release of the formed part from the forming tool. As metal deformation and temperature increase, however, the ability of the lubricant to perform these functions is significantly inhibited. This is due in part to fresh reactive metal being exposed and the thickness of the lubricant film being reduced during the metal deformation process and to the lubricant's organic components rapidly degrading due to the elevated temperature. Even solid lubricants, such as graphite or boron nitride, also suffer from a number of problems despite their high thermal stability. For instance, solid lubricants are difficult to apply uniformly onto the metal product, may adhere poorly once applied, and may not spread readily to provide lubrication to newly formed surfaces. The utilization of solid lubricants in a forming process can also lead to frequent manufacturing line interruptions because of lubricant accumulation on the forming tool. Additionally, solid lubricant residue can interfere with downstream processing and finishing. Furthermore, some solid lubricants can promote corrosion of the surface of the metal product onto which they are applied. Finally, in an industrial environment, solid lubricants not only present inhalation risks but they can also present challenges to safety and housekeeping by being difficult to clean from the work environment.
Therefore, there exists a need for a method that reduces or eliminates the amount of lubricants used during a forming process. There also exists a need for a method that reduces or eliminates the amount of lubricants used during a forming process and that is compatible with the downstream processes to which the metal is subjected.
This invention responds to these needs by disclosing a method of using oxides that are generated electrochemically on the surface of an aluminum product thereby reducing or eliminating the need for using lubricants during the forming process.

SUMMARY OF THE INVENTION

This invention discloses a method for preparing a metal product for forming that includes providing a metal product and anodically generating an oxide layer on at least one surface of the product.
This invention also discloses a method for reducing or eliminating the amount of lubricants used during a forming process that includes providing a metal product having at least one surface, anodically generating an oxide layer on the surface of the product, and forming the metal product into a shape using a forming process.
This invention also discloses a metal product suitable for forming that includes an oxide layer on at least one surface of the metal product, the oxide layer being anodically generated on the surface of the metal product prior to forming the metal product into a desired shape using a forming process.
One aspect of this invention is to reduce the costs, e.g. labor costs, lubricant costs, and process inconsistencies, associated with metal forming by reducing or eliminating the need of having to purchase and apply a lubricant to the surface of the metal prior to a forming process.
Another aspect of this invention is to eliminate the step of having to remove and dispose of excess lubricant that has remained on the surface of the metal workpiece prior to subsequent, i.e. post-forming, processing steps.
Another aspect of this invention is the generation of a surface film on the surface of the metal product, which can provide protection against corrosion and scratching.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the coefficient of friction (COF) at a temperature of about 454° C. (849.2° F.) of aluminum alloy 5083 with and without an anodized oxide coating.
FIG. 2 depicts the coefficient of friction (COF) at a temperature of about 454° C. (849.2° F.) of 6XXX aluminum automotive sheet rolled with electrical discharge textured (EDT) rolls.
FIG. 3 depicts the coefficient of friction (COF) at a temperature of about 454° C. (849.2° F.) of 6XXX aluminum automotive sheet, which has been coated with various commercially available conversion coatings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The accompanying figures and the description that follow set forth this invention in its preferred embodiments. However, it is contemplated that persons generally familiar with metal forming and anodizing techniques will be able to apply the novel characteristics of the structures and methods illustrated and described herein in other contexts by modification of certain details. Accordingly, the figures and description are not to be taken as restrictive on the scope of this invention, but are to be understood as broad and general teachings. When referring to any numerical range of values, such ranges are understood to include each and every number and/or fraction between the stated range minimum and maximum.
This invention discloses using an oxide layer that is generated electrochemically on one or more surfaces of an aluminum product to supplement the natural oxide layer and to minimize the need for lubricating the aluminum product prior to a forming process. Based on anodizing conditions, the electrochemically generated oxide layer can be either porous or non-porous. For clarity, the oxide layer that is generated electrochemically on the surface of the aluminum product shall be referred to as the enhanced oxide layer hereafter. The enhanced oxide layer is formed on the aluminum product using anodizing techniques that are commonly known in the art. For instance, batch processing whereby individual panels or pieces are anodized as well as coil anodizing may be used with the disclosed invention. Additionally, the anodizing process that is used in conjunction with this invention may also use an electrical current that is either a direct current (DC) or an alternating current (AC). The anodizing technique can be used to manipulate the oxide layer's physical properties by controlling variables such as bath composition, concentration, temperature, current density, use of direct or alternating electrical current, electrode geometry, and the total amount of time the metal product is exposed to the anodizing process. Additionally, subsequent processes, e.g. a sealing process, can alter the properties of the enhanced oxide layer in order to provide other benefits such as increased corrosion resistance.
The inventors of this invention hypothesize that a suitable oxide layer can provide enhanced forming performance when compared to the naturally occurring oxide layer in aluminum workpieces. Additionally, the inventors believe that such an oxide layer can reduce or completely remove the need for having to add a lubricant prior to a forming process. It is noted that this invention is not limited to hot or cold forming processes but that it may be applied to any forming process where control or reduction of the coefficient of friction is needed and the tendency for metal transfer to the tooling is present. For instance, processes that involve sheet or plate forming, drawing or stamping as well as forging and extruding would most likely benefit from the disclosed invention.
FIG. 1 depicts the coefficient of friction of aluminum alloy 5083 with and without an anodically generated oxide coating, i.e. an enhanced oxide layer. The enhanced oxide coatings can be generated on the surface of the 5083 alloy using techniques that are commonly known in the art. In these trials, the aluminum 5083 workpiece, which acted as an anode, was submerged in a tank that contained an electrolyte and was equipped with a copper cathode. The electrolyte that can be used to form the oxide layer would include sulfuric acid, oxalic acid, phosphoric acid, neutral borate, chromic acid, or mixtures thereof. Additionally, the electrolyte solution could also have one or more additives. A direct current (DC) and/or an alternating current (AC) power supply was then attached to the aluminum product thereby creating a circuit. The enhanced oxide layer was generated electrochemically on the surface of the aluminum alloy by applying a current through the metal workpiece.

Method for Measuring the Coefficient of Friction

In each of the following trials, the coefficient of friction of the aluminum product was measured using the following method. First, the aluminum product was heated in a furnace that was set to a temperature of about 454° C. (849.2° F.). The aluminum product was held at this temperature for about 15 to 20 minutes in order to stabilize the temperature of the product. While in the furnace, the coefficient of friction of the aluminum product was obtained using a sliding contact test in which an array of tooling specimens traveled across the surface of the product in a direction substantially perpendicular to the rolling direction. The frictional force was measured by a transducer that was attached to the tooling piece and recorded into a computer program. The computer program was used to generate the coefficient of friction, which is shown in FIG. 1, between the contacting surfaces of the tooling piece and the aluminum product by taking the average of the frictional force as measured by the transducer over the course of the test and dividing that average by the weight of the tooling piece. Factors such as temperature, load, the presence or absence of lubricant on the surface of the product, sliding speed of the tooling piece, contact geometry, tooling material, and surface topography are all manipulated in order to simulate a given forming process. In this invention, the COF values attributed to the aluminum products in Trials 1-21 were obtained under substantially identical contact conditions with the tooling specimen array described above.

Enhanced Oxide Layer Integrity (Film Integrity) and Enhanced Oxide Layer Thickness

In each of the trials involving an anodized oxide layer (i.e. an enhanced oxide layer) on the surface of the aluminum product, the integrity of the enhanced oxide layer was evaluated with a microscope to determine to what extent the tooling piece stripped the enhanced oxide layer from the surface of the aluminum product during the sliding contact test described in the preceding paragraph. If the tooling piece had no visual effect on the enhanced oxide layer, i.e. the enhanced oxide layer remained intact and attached to the surface of the specimen, then a rating of “excellent” was given to that trial. Conversely, if the tooling piece stripped or scraped the enhanced oxide layer completely from the surface of the product and/or disrupted the surface of the product at the areas of contact, then a rating of “poor” was given to that particular trial. Finally, if the tooling piece partially stripped the enhanced oxide layer from the surface of the aluminum product, then a rating of “fair” or “good” was given to the trial.
The thickness of the oxide layer in trials 2-13 was measured using a Permascope instrument.

Pre-Treatment

Prior to anodizing the surface of the 5083 alloy, the surfaces of the alloy were cleaned for about 2 minutes at about 60° C. (140° F.) with Henkel Surface Technologies' (32100 Stephenson Hwy, Madison Heights, Mich. 48071) A31K cleaner, which is a non-etching alkaline medium containing borate, phosphate, and sulfate. Excess A31K cleaner was removed by submerging the aluminum alloy in a tank of deionized water and later rinsing the surfaces of the alloy with additional deionized water.

Trial 1

In trial #1, a bare 5083 aluminum alloy with an as-rolled surface texture was used to create a base line against which the coefficient of friction of the other trials may be compared. In other words, the 5083 aluminum alloy in trial #1 does not have the enhanced oxide layer on any surface of the alloy. The surface of the bare 5083 alloy was cleaned using the method that is described in the previous paragraph. The cleaned alloy was then placed in a heating furnace and the coefficient of friction of the bare 5083 alloy was obtained using the sliding contact test as described above. As can be seen from FIG. 1, bare 5083 aluminum alloy (trial #1) had a coefficient of friction of about 1.58 at temperature of about 454° C. (849.2° F.).

Trials

2 and 3

The next two trials involved creating a barrier coating, which served as an enhanced oxide layer, on the surface of the 5083 alloy. In trial #2, an enhanced non-porous oxide layer was generated anodically on the aluminum product by submerging the product in a neutral borate solution medium that was at a temperature of about 22.2° C. (72° F.). The solution medium was prepared by adding about 20 grams per liter of boric acid to deionized water and adding sodium borate until the solution had a pH of about 6.8. After submerging the aluminum product in the solution medium, a direct electrical current having a potential of about 50 volts was applied to the aluminum product for about 2 minutes until the current diminished thereby generating on the surface of the aluminum product an enhanced non-porous oxide layer having a thickness of about 0.07 μm. Once the enhanced oxide layer was generated on the surface of the 5083 aluminum product, the coefficient of friction was measured using the method that is disclosed above. As can be seen in FIG. 1, the coefficient of friction of the product in trial #2 was about 1.24 at a temperature of about 454° C. (849.2° F.). This is a reduction in friction of about 22% when compared to bare 5083 aluminum alloy in trial #1. With regards to film integrity, trial #2 was given a rating of “poor” since the enhanced oxide layer was stripped from the aluminum product during the sliding contact test.
In trial #3, the solution medium in which the aluminum product was submerged was prepared in the same manner as described in the preceding paragraph. However, in trial #3 the electrical potential that was applied to the aluminum product was doubled to about 100 volts, which was applied to the aluminum product for about 4 minutes until the current diminished. The resulting enhanced oxide layer had a thickness of about 0.14 μm. As can be understood from FIG. 1, the coefficient of friction of the product in trial #3 was about 1.13, which is a reduction in friction of about 29% when compared to bare 5083 aluminum (trial #1) and about an 9% reduction in friction when compared to the aluminum product in trial #2. Similar to trial #2, the sliding contact test stripped the enhanced oxide layer in trial #3 from the surface of the aluminum product. Accordingly, trial #3 received a rating of “poor” with regards to film integrity.

Trials

4, 5, and 6

These three trials involved submerging the 5083 aluminum product in a tank containing a 20% by weight sulfuric acid (H₂SO₄) solution, which was held at a temperature of about 32.2° C. (90° F.). After the product was submerged in the sulfuric acid solution an electrical current was applied to the aluminum product to form an enhanced porous oxide layer on the surface of the product.
In trial #4, the enhanced oxide layer was generated on the surface of the 5083 aluminum product by applying a direct electrical current of about 24 amps per square foot for about 2.5 to about 3 minutes to form an enhanced oxide layer having a thickness of about 2.0 μm. The aluminum product containing the enhanced oxide layer was then placed in a heating furnace and the coefficient of friction of the 5083 alloy was obtained using the sliding contact test as described above. Referring to FIG. 1, the coefficient of friction of the aluminum alloy in trial #4 was about 0.87 at a temperature of about 454° C. (849.2° F.). When compared to the bare 5083 aluminum alloy in trial #1, the aluminum product in trial #4 exhibited about a 45% reduction in friction. When compared to the aluminum product in trial #3, the aluminum product in trial #4 exhibited about a 23% reduction in friction. Because the enhanced oxide layer in trial #4 remained somewhat intact during the sliding contact test, trial #4 was given a film integrity rating of “fair.”
Trial #5 involved applying a direct electrical current of about 24 amps per square foot to the 5083 aluminum product for about 15 minutes to generate an enhanced oxide layer having a thickness of about 16 μm on the surface of the aluminum product. As can be seen from FIG. 1, the aluminum product in trial #5 had a coefficient of friction of about 0.60 at a temperature of about 454° C. (849.2° F.). When compared to bare 5083 aluminum (trial #1), the aluminum product in trial #5 had about a 62% reduction in friction. When compared to the aluminum product in trial #4, the aluminum product in trial #5 had about a 31% reduction in friction. Because the enhanced oxide layer remained intact during the sliding contact test, trial #5 was given a film integrity rating of “excellent.”
Similar to trials #4 and #5, the oxide layer in trial #6 was generated on the surface of the 5083 aluminum product by applying a direct electrical current of about 24 amps per square foot. However, unlike trials #4 and #5 the electric current in trial #6 was applied for about 20 minutes. The resulting enhanced oxide layer had a thickness of about 58 μm. As can be understood from FIG. 1, trial #6 had a coefficient of friction of about 0.72 at a temperature of about 454° C. (849.2° F.), which is a reduction of about 54% in friction when compared to the bare 5083 aluminum alloy in trial #1, and about a 17% reduction in friction when compared to the aluminum product in trial #4. Trial #6 was given a film integrity rating of “excellent” since the enhanced oxide layer remained intact during the sliding contact test.

Trials

7 and 8

In trials 7 and 8, the 5083 aluminum products were treated electrochemically to generate an enhanced porous oxide layer containing tin. The enhanced oxide layer was initially generated on the aluminum product by submerging the aluminum product in a tank containing a 20% by weight sulfuric acid solution held at a temperature of about 21.1° C. (70° F.). After submerging the 5083 product into the tank, a direct electrical current of about 12 amps per square foot was applied to the aluminum product. The aluminum product was then transferred to a second tank containing a stannous sulfate solution that was held at a temperature of about 22.2° C. (72° F.) and had a pH of about 1.0. The stannous sulfate solution contained about 20 grams per liter of sulfuric acid, 20 grams per liter of stannous sulfate, and 20 grams per liter of a stabilizing agent. In trials 7 and 8, the stabilizing agent that was used in the stannous sulfate solution was catechol. Once the aluminum product was submerged in the second tank, the 5083 aluminum products were subjected to an alternating electrical current ranging from about 5 amps per square foot to about 7 amps per square foot.
In trial #7, an enhanced tin-containing oxide layer having a thickness of about 3.3 μm was generated on the surface of the 5083 aluminum product by applying the alternating electrical current for about 3 minutes to the product generated using direct current in the preceding paragraph. After the enhanced tin-containing oxide layer had been generated on the surface of the aluminum product, the coefficient of friction was determined using the sliding contact test described above. Referring to FIG. 1, the aluminum product in trial #7 had a coefficient of friction of about 0.70 at a temperature of about 454° C. (849.2° F.), which is about a 56% reduction in friction when compared to the bare 5083 aluminum alloy in trial #1. Trial #7 was given a film integrity rating of “fair” since the enhanced oxide layer remained somewhat intact during the sliding contact test.
Trial #8 involved applying an alternating electrical current for about 20 minutes to the direct current anodized 5083 aluminum product in order to generate an enhanced oxide layer containing tin having a thickness of about 30 μm on the surface of the product. As can be understood from FIG. 1, the aluminum product in trial #8 had a coefficient of friction of about 0.68 at a temperature of about 454° C. (849.2° F.). This is a reduction in friction of about 57% when compared to bare 5083 aluminum (trial #1), and about a 3% reduction when compared to the aluminum product in trial #7. Similar to trial #7, the enhanced oxide layer in trial #8 was given a film integrity rating of “fair.”

Trials

9 and 10

The 5083 aluminum products in trials #9 and #10 were submerged in a tank containing a 5% oxalic acid solution, which was held at a temperature of about 20° C. (68° F.). A direct current at a potential of about 40 volts was then applied to the 5083 aluminum product to form an enhanced porous oxide layer on the surface of the product.
In trial #9, the 40 volt potential was applied to the aluminum product for about 3 minutes thereby producing an enhanced oxide layer having a thickness of about 3.5 μm. Once the enhanced oxide layer was generated on the surface of the 5083 aluminum product, the coefficient of friction was measured using the method that is disclosed above. As can be understood from FIG. 1, the 5083 product in trial #9 had a coefficient of friction of about 0.68 at a temperature of about 454° C. (849.2° F.). This is a reduction of about 57% in friction when compared to the bare 5083 aluminum in trial #1. With regards to film integrity, trial #9 was given a rating of “fair” since the enhanced oxide layer remained partially intact after the sliding contact test was completed.
Trial #10 involved applying the 40 volt potential to the aluminum product for about 60 minutes. The resulting enhanced oxide layer that was produced had a thickness of about 58 μm. As can be seen in FIG. 1, the coefficient of friction of the coated 5083 aluminum product in trial #10 was about 0.55 at a temperature of about 454° C. (849.2° F.), which is a reduction of about 65% in friction when compared to bare 5083 aluminum (trial #1) and about a 19% reduction in friction when compared to the aluminum product in trial #9. Similar to trials #5 and #6, the enhanced oxide layer in trial #10 was given a film integrity rating of “excellent” since the enhanced oxide layer was not stripped from the aluminum product during the sliding contact test.

Trials

11, 12, and 13

In these three trials, the 5083 aluminum alloy product was submerged in a 20% by weight phosphoric acid solution that was held at a temperature of about 29.4° C. (85° F.). Air agitation was used to draw the heat that was generated from the electrochemical reaction during the anodizing process away from the surface of the aluminum product in order to provide uniform temperature conditions at the metal surface. The resulting enhanced porous oxide layers in each of these trials had a thickness of less than about 1.2 μm.
Trial #11 involved applying a direct current at a potential of about 15 volts to the aluminum product for about 1 minute. After the enhanced oxide layer had been generated on the surface of the 5083 product, the coefficient of friction was determined using the method that is described above. As can be seen in FIG. 1, trial #11 had a coefficient of friction of about 1.21 at a temperature of about 454° C. (849.2° F.). This is a reduction of about 23% in friction when compared to the bare 5083 aluminum in trial #1. Because the enhanced oxide layer in trial #11 was stripped from the aluminum product during the sliding contact test, trial #11 was given a film integrity rating of “poor.”
In trial #12, a direct current having a potential of about 15 volts was applied to the aluminum product for about 10 minutes. As can be seen in FIG. 1, the aluminum product in trial #12 had a coefficient of friction of about 1.02 at a temperature of about 454° C. (849.2° F.), which is a reduction of about 35% in friction when compared to bare 5083 aluminum (trial #1) and a 16% reduction in friction when compared to the aluminum product in trial #11. Trial #12 received a film integrity rating of “fair” since the enhanced oxide layer remained somewhat intact during the sliding contact test.
Trial #13 involved applying a direct current of about 15 volts to the aluminum product for about 20 minutes. As FIG. 1 depicts, the coefficient of friction of trial #13 was about 1.00 at a temperature of about 454° C. (849.2° F.). This is a reduction of about 37% when compared to bare 5083 aluminum (trial #1), about a 16% reduction in friction when compared to the aluminum product in trial #11, and a reduction of about 2% in friction when compared to the aluminum product in trial #12. Because the enhanced oxide layer remained somewhat intact during the sliding contact test, trial #13 was given a film integrity rating of “fair.”
Trials 2-13 all show that an enhanced oxide layer that is generated on the surface of the 5083 aluminum product can decrease the coefficient of friction of the product by about 23% to about 65% when compared to bare 5083 aluminum alloy. Because the amount of friction is substantially reduced when the oxide layer is present on the surface of the aluminum product, the amount of lubricant needed to protect the aluminum product during a forming process can be reduced or eliminated.

Trials

14, 15, 16, and 17

Trials 15-17 involved measuring the coefficient of friction of three automotive sheet samples corresponding to a single alloy in the Aluminum Association's 6XXX series that were imprinted with electrical discharge textured (EDT) rolls having a Ra roughness of about 0.51 μm, 0.84 μm, and 1.12 μm. The goal of trials 15-17 was to determine the effect the texture imparted by the electro-discharge texturing rolls had in lowering the coefficient of friction of the aluminum sheet without an enhanced oxide layer generated on the surface of the sheet. In each of these trials, the coefficient of friction was obtained using the sliding contact test that was used in the previous trials.
In trial #14, the coefficient of friction of bare 6XXX aluminum sheet was measured using the sliding contact test that is described above. Unlike trials 15-17, the aluminum sheet in trial #14 was rolled with rolls having a typical ground surface used in normal rolling mill operations. As can be understood from FIG. 2, bare 6XXX aluminum alloy with the typical rolled surface texture had a coefficient of friction of about 2.61 at a temperature of about 454° C. (849.2° F.).
The surface of the 6XXX aluminum sheet in trial #15 had a Ra roughness of about 0.51 μm (20 μin.). As can be seen in FIG. 2, the aluminum sheet in trial #15 had a coefficient of friction of about 2.61 at a temperature of about 454° C. (849.2° F.), which is the same coefficient of friction exhibited by the 6XXX aluminum sheet in trial #14.
In trial #16, the surface of the 6XXX aluminum sheet had a Ra roughness of about 0.84 μm (33 μin.). Referring to FIG. 2, the aluminum sheet in trial #16 had a coefficient of friction of about 2.49 at a temperature of about 454° C. (849.2° F.). This is about a 5% reduction in friction when compared to bare 6XXX aluminum (trial #14).
The surface of the 6XXX aluminum sheet in trial #17 had a Ra roughness of about 1.12 μm (44 μin.). Similar to trials 14 and 15, the aluminum sheet in trial #17 had a coefficient of friction of about 2.61 at a temperature of about 454° C. (849.2° F.).
Unlike the trials that had an enhanced oxide layer generated by anodizing the surface of the aluminum product, the modified surface texture on 6XXX sheet imparted by EDT rolls in these trials afforded little protection against the friction that was generated by the sliding contact test. Even though trials 14-17 involved the use of 6XXX aluminum as opposed to 5083 aluminum (trials 2-13), it is hypothesized that the EDT texture would provide an equivalent amount of protection to a 5083 aluminum alloy. In other words, without the use of lubrication or some other type of coating the EDT texture would provide minimal to no protection to a 5083 aluminum alloy that is undergoing a forming process. From the test results obtained from trials 14-17, one skilled in the art would appreciate the protective benefits of having an enhanced oxide layer generated on a surface of the aluminum alloy by anodizing as opposed to having the pattern from EDT rolls imparted into the surface of the aluminum alloy.

Trials

18, 19, 20, and 21

The goal of these trials was to determine what affect a selected commercially available conversion coating treatment would have in lowering the coefficient of friction of an aluminum workpiece. In trials 19-21, the conversion coating was applied onto a single 6XXX aluminum product at a maximum thickness of about 0.1 μm. As in the previous trials, the coefficient of friction of the aluminum sheet in trials 18-21 was obtained using the sliding contact test that is described above.
In trial #18, the coefficient of friction of bare 6XXX aluminum sheet was measured in order to provide a baseline to which trials 19-21 may be compared. As can be understood from FIG. 3, bare 6XXX aluminum alloy had a coefficient of friction of about 2.61 at a temperature of about 454° C. (849.2° F.).
The 6XXX aluminum sheet in trial #19 was coated with a Henkel B1453 conversion coating. Henkel B1453 is a titanium and zirconium based coating containing silicates and some organic particles. The Henkel B1453 conversion coating may be obtained from Henkel Surface Technologies, 32100 Stephenson Highway, Madison Heights, Mich. 48071. In this trial, the coating was applied onto the aluminum product at 7.7 msf (mg per square foot). As depicted in FIG. 3, the coefficient of friction of trial #19 was about 1.61 at a temperature of about 454° C. (849.2° F.). This is about a 38.3% reduction in friction when compared to the aluminum sheet in trial #18. Despite the overall reduction in friction, however, the aluminum sheet in this trial exhibited severe scarring on the surface of the aluminum product. This indicates that the tooling piece scraped the conversion coating from the surface of the aluminum sheet along the lines of contact during the sliding contact test.
Trial #20 involved coating the aluminum sheet with a Chemetall Oakite X4591 conversion coating. Similar to the Henkel B1453 coating, the Chemetall coating is also titanium and zirconium based. In addition, the coating weight of X4591 is substantially similar to the coating weight of the Henkel conversion coating. The Chemetall Oakite X4591 conversion coating may be obtained from Chemetall Oakite, 50 Valley Rd., Berkeley Heights, N.J. 07922. As can be seen in FIG. 3, testing of the aluminum sheet in trial #20 yielded a coefficient of friction of about 1.56, which is a reduction of about 40.2% in friction when compared to the 6XXX aluminum sheet in trial #18 and about a 3% reduction in friction when compared to the aluminum sheet in trial #19. Similar to trial #19, the surface of the 6XXX aluminum sheet in this trial also exhibited severe scarring due to the contact with the tooling piece used in the sliding contact test.
In trial #21, the 6XXX aluminum sheet was coated with a Permatreat 1021B conversion coating. The Permatreat 1021B conversion coating may be obtained from Betz-Dearborn Inc., 4636 Somerton Road, Trevose, Pa. 19053. Unlike the Henkel or the Chemetall Oakite conversion coatings used in trials 19 and 20, respectively, Permatreat 1021B is a fluorotitanate based coating having a coating weight of about 10 msf. As depicted in FIG. 3, testing of the 6XXX aluminum sheet in trial #21 yielded a coefficient of friction of about 1.71. This is a reduction of about 34.5% in friction when compared to the aluminum sheet in trial #18. However, this is an increase in friction of about 6% when compared to trial #19 and about a 9.6% increase in friction when compared to trial #20. The surface of the aluminum sheet in this trial, similar to trials 19 and 20, exhibited severe scarring along the contact areas after the sliding contact test was complete.
Unlike the trials that involved anodically generating an oxide layer over the surface of the aluminum product, the conversion coatings in trials 19-21 afforded little protection against the conditions that were generated during the sliding contact test. Additionally, the conversion coatings failed to prevent the tooling piece from severely damaging the surface of the underlying aluminum product.
In one embodiment, the enhanced oxide layer can have a thickness up to about 100 μm.
In another embodiment, the thickness of the oxide layer ranges from about 2 μm to about 60 μm.
Having described the presently preferred embodiments, it is to be understood that the invention may be otherwise embodied within the scope of the appended claims.

Claims

1. A method for reducing or eliminating the amount of lubricants used during a forming process comprising:

providing a metal product;

anodically generating an oxide layer on at least one surface of said metal product; and

forming said metal product into a shape using said forming process.

2. A method for reducing or eliminating the amount of lubricants used during a forming process according to claim 1 wherein providing a metal product, said metal product being an aluminum or an aluminum alloy.

3. A method for reducing or eliminating the amount of lubricants used during a forming process according to claim 2 wherein providing an aluminum alloy selected from the group consisting essentially of the Aluminum Association's 1XXX, 2XXX, 3XXX, 4XXX, 5XXX, 6XXX, 7XXX, or 8XXX series of aluminum alloys.

4. A method for reducing or eliminating the amount of lubricants used during a forming process according to claim 1 wherein said surface is partially or fully immersed in an electrolyte solution.

5. A method for reducing or eliminating the amount of lubricants used during a forming process according to claim 4 wherein anodizing said surface of said metal product in an electrolyte solution selected from the group consisting essentially of sulfuric acid, oxalic acid, phosphoric acid, neutral borate, and chromic acid.

6. A method for reducing or eliminating the amount of lubricants used during a forming process according to claim 1 wherein anodizing to generate an oxide layer having a thickness up to about 100 μm.

7. A method of preparing a metal product for forming according to claim 1 wherein generating an oxide layer containing tin on said surface of said metal product.

8. A method for reducing or eliminating the amount of lubricants used during a forming process according to claim 1 wherein forming said metal product using a forming process.

9. A method for reducing or eliminating the amount of lubricants used during a forming process according to claim 8 wherein forming said metal product using a forming process selected from the group consisting essentially of hot forming, cold forming, sheet forming, plate forming, forging, or extruding.

10. A method for reducing or eliminating the amount of lubricants used during a forming process according to claim 1 wherein providing a metal product, said metal product being a sheet, plate or a pre-form for an extrusion or forging process.

11. A method for reducing or eliminating the amount of lubricants used during a forming process according to claim 1 further comprising applying a lubricant onto said oxide layer prior to forming.

12. A metal product suitable for forming comprising:

an oxide layer on at least one surface of said metal product, said oxide layer being anodically generated on said surface of said metal product prior to forming said metal product into a desired shape using a forming process.

13. A metal product suitable for forming according to claim 12 wherein said metal product is aluminum or an aluminum alloy.

14. A metal product suitable for forming according to claim 13 wherein said aluminum alloy is selected from the group consisting essentially of the Aluminum Association's 1XXX, 2XXX, 3XXX, 4XXX, 5XXX, 6XXX, 7XXX, or 8XXX series of aluminum alloys.

15. A metal product suitable for forming according to claim 12 wherein said anodizing process involves dipping or immersing said surface of said metal product in an electrolyte.

16. A metal product suitable for forming according to claim 15 wherein said electrolyte is selected from the group consisting essentially of sulfuric acid, oxalic acid, phosphoric acid, neutral borate, and chromic acid.

17. A metal product suitable for forming according to claim 12 wherein said oxide layer has a thickness up to about 100 μm.

18. A metal product suitable for forming according to claim 12 wherein said oxide layer contains tin.

19. A metal product suitable for forming according to claim 12 wherein said metal product is formed into a desired shaping using a forming process.

20. A metal product suitable for forming according to claim 19 wherein said forming process is from the group consisting essentially of hot forming, cold forming, sheet forming, plate forming, forging, or extruding.

21. A metal product suitable for forming according to claim 12 wherein said metal product is a sheet, plate or a pre-form for an extrusion or forging process.

22. A metal product suitable for forming according to claim 12 further comprising a lubricant applied onto said oxide layer prior to forming.

23. A method of preparing a metal product for forming comprising:

providing a metal product having at least one surface; and

anodically generating an oxide layer on said surface of said metal product.