Metal working – Method of mechanical manufacture – Assembling or joining
Utility Patent
1997-12-26
2001-01-02
Rosenbaum, Irene Cuda (Department: 3726)
Metal working
Method of mechanical manufacture
Assembling or joining
C029S527200
Utility Patent
active
06167609
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for joining aluminum alloy extrusions, castings, sheet and plate into structures suitable for use as vehicle components. More particularly, the invention concerns an improved method for pretreating aluminum alloy components to promote adhesive bonding.
BACKGROUND OF THE INVENTION
Aluminum alloy components are finding increased use in automotive and aircraft applications because they are light and have high strength. Vehicle manufacturers join the aluminum alloy components permanently with polymeric adhesives, or they join the components temporarily with adhesives before welding them. Some manufacturers employ chromium-containing chemicals to treat aluminum alloy surfaces in order to achieve durable adhesive bonds. Environmental concerns about hexavalent chromium are expected to render obsolete the chromium pretreatments.
The present invention relates to a non-chromium pretreatment for improving the adhesive bonding of aluminum alloy components. A prior art process for pretreating aluminum alloy sheet with chromium compounds is disclosed in Selwood U.S. Pat. Nos. 5,026,612 and 5,139,888. A non-chromate pretreatment process for aluminum alloy sheet is disclosed in McCleary U.S. Pat. No. 5,463,804, issued Nov. 7, 1995. The McCleary patent is incorporated herein by reference, to the extent consistent with the present invention.
The process of our invention is useful for treating aluminum alloy extrusions, castings, sheet and plate. As used herein, the term “sheet” refers to aluminum alloy material having a thickness of about 0.006 to 0.249 inch. The term “plate” refers to flat aluminum alloy material having a thickness of about 0.25 inch or more.
The primary criterion for evaluating the effectiveness of an aluminum alloy pretreatment is adhesive bond durability. It is also important that the surface treatment not be detrimental to downstream processes. For example, a sheet surface treatment must not inhibit stamping and forming the sheet. The surface treatment must remain intact during those operations. Resistance spot welding is often used in combination with adhesive bonding to improve peel strength. The pretreatment must not significantly reduce the quality of the welds or reduce the life expectancy of welding electrodes. It is also critical that the pretreatment not be detrimental to the chemical baths required for zinc phosphating and electrocoating before paint is applied.
A principal objective of the present invention is to provide a process for adhesively joining magnesium-containing aluminum alloy components.
A related objective of the invention is to provide a pretreatment for a heat treated aluminum alloy components that will improve adhesive bond durability.
Additional objectives and advantages of our invention will be readily apparent to persons skilled in the at from the following detailed description of a particularly preferred embodiment.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided an improved process for adhesively bonding aluminum alloy components. As used herein, the term “aluminum alloy” refers to an alloy containing about 85 wt. % or more aluminum and one or more alloying elements that are not subversive to organophosphorus surface treatments. Some suitable alloying elements are copper, manganese, magnesium. silicon, zinc, and lithium. These alloying elements are sometimes called character imparting because alloys containing them derive their characteristic properties from such elements.
Usually, the amounts of such alloying elements are, as to each of magnesium, copper and zinc, about 0.5 to 10% by weight of the total alloy; as to the element manganese, usually about 0.15 to 2% of the total alloy; as to silicon, usually about 0.25 to 15% of the total alloy; and, as to the element lithium, about 0.2 to 3% of the total alloy. Iron and beryllium may also be present in aluminum alloys and can have a marked effect upon alloys containing them. Iron, for example, is often adjusted in amounts of about 0.3 to 2.0% by weight to perform specific functions and beryllium may be present in amounts of about 0.001 to 5.0% of the total alloy.
Various aluminum alloys available in sheet form are suitable for practice of the present invention, including alloys belonging to the AA2000, 3000, 5000, 6000 and 7000 series. Alloys of the AA6000 series containing about 0.4 to 1.5 wt. % magnesium and about 0.3 to 1.5 wt. % silicon are preferred. This group of alloys includes AA alloy 6022 containing 0.45-0.7 wt. % Mg, 0.8-1.5 wt. % Si, 0.01-0.11 wt. % Cu, and 0.02-0.10 wt. % Mn; and AA alloy 6111 containing 0.5-1.0% Mg, 0.7-1.1% Si, 0.50-0.90% Cu and 0.15-0.45% Mn. Another useful group of alloys is the AA5000 series. One preferred example is AA alloy 5182 which contains 4.0-5.0 wt. % Mg and 0.20-0.50 wt. % Mn.
Various aluminum alloy castings are suitable for practice of our invention, including die castings, sand castings and permanent mold castings. One suitable alloy is alloy number A356 with a nominal composition of 7.0 wt. % Si, 0.3 wt. % Mg, 0.17 wt. % max. Fe, 0.17 wt. % max. Cu, remainder aluminum, incidental elements, and impurities. The A356 alloy castings are commonly solution heat treated or aged at an elevated temperature before use. Two other useful alloys are C119 containing 9-10.5 wt. % Si, and 0.10-0.20 wt. % Mg; and C448 containing 9.0-11.5 wt. % Si, 0.40-0.80 wt. % Mn and 0.10-0.35 wt. % Mg.
Aluminum alloy extrusions suitable for practice of the invention are preferably made from alloys containing silicon and magnesium in proportions making them heat treatable, such as the AA6000 series of aluminum alloys. In particular, the AA6009, 6010, 6061, 6063 and similar alloys are useful. The AA6061 and 6063 aluminum alloys are particularly preferred. Other useful alloys include C210 containing 0.40-0.60 wt. % Si, 0.15-0.25 wt. % Cu, 0.40-0.60 wt. % Mg, and 0.15-0.25 wt. % Fe; and C461 containing 0.4-0.6 wt. % Si, 0.15-0.40 wt. % Fe, 0.45-0.70 wt. % Mg, and 0.10-0.25 wt. % V.
Aluminum alloy extrusions are typically made by a process wherein a heated ingot or billet is forced through a die opening under pressure to form an elongated body such as a channel or tube. The extruded product is generally forced through a die at forces in the 500 to 15,000 ton range. The extruded product is commonly solution heat treated and quenched after it leaves the extrusion die.
Heat treated aluminum alloy sheet, plate, extrusions, and castings are left with a surface layer comprising a mixture of metal oxides. Chemical composition of the surface layer will vary, depending upon the alloy. Typically, magnesium oxide predominates over aluminum oxide. The Mg:Al atomic ratio is generally about 1.5:1 to 3:1. The surface layer has a thickness of up to a few hundred angstroms.
We pretreat aluminum alloy sheet, plate, extrusions and castings with a phosphorus-containing organic acid before joining the pretreated body to a metal support structure, using a polymeric adhesive. In order to improve adhesion, the surface layer is treated with an acidic solution before applying the organic acid. The acidic solution is preferably an aqueous solution of one or more of phosphoric, sulfuric, nitric, and hydrofluoric acids, and mixtures thereof The solution generally has a pH of about 0-4. We rinse the acid treated surface layer with water. After surface preparation, a surface layer with reduced magnesium oxide content remains on the component.
We then pretreat the surface layer with a phosphorus-containing organic acid. The organic acid interacts with aluminum oxide in the surface layer to form a functionalized layer. The organic acid is dissolved in water, methanol, or other suitable organic solvent, to form a solution that is applied to the component by spraying, immersion, or roll coating. The phosphorus-containing organic acid may be an organophosphonic acid or an organophosphinic acid. The pretreated body is then rinsed with water after the pretreatment application step.
The term “organophosphonic acid” in
Costrini John V.
Marinelli James M.
McCleary Sherri F.
Nitowski Gary A.
Siemon John T.
Aluminum Company of America
Cuda Rosenbaum Irene
Klepac Glenn E.
Nguyen Trinh T.
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