ALUMINUM-MAGNESIUM-ZINC ALUMINUM ALLOYS

Abstract

New aluminum alloys having magnesium and zinc are disclosed. The new magnesium-zinc aluminum alloys may include from 2.5 to 4.0 wt. % Mg, from 2.25 to 4.0 wt. % Zn, wherein (wt. % Mg/wt. % Zn)≥1.0, and wherein (wt. % Mg/wt. % Zn)≤1.6, from 0.20 to 0.9 wt. % Mn, from 0.10 to 0.40 wt. % Cu, up to 1.0 wt. % Li, up to 0.50 wt. % Fe, up to 0.50 wt. % Si, and optional secondary element(s), the balance being aluminum, optional incidental elements and impurities.

Claims

1. An aluminum alloy comprising: from 2.5 to 4.0 wt. % Mg; from 2.25 to 4.0 wt. % Zn; wherein (wt. % Mg/wt. % Zn)≥1.0; and wherein (wt. % Mg/wt. % Zn)≤1.6; and from 0.20 to 0.9 wt. % Mn; from 0.10 to 0.40 wt. % Cu; up to 1.0 wt. % Li; up to 0.50 wt. % Fe; up to 0.50 wt. % Si; optionally at least one secondary element selected from the group consisting of Zr, Sc, Cr, Hf, V, Ti, and rare earth elements, and in the following amounts: up to 0.20 wt. % Zr; up to 0.30 wt. % Sc; up to 0.50 wt. % Cr; up to 0.25 wt. % each of any of Hf, V, and rare earth elements; up to 0.15 wt. % Ti; the balance being aluminum, optional incidental elements and impurities.

2. The aluminum alloy product of claim 1, wherein the aluminum alloy comprises less than 0.01 wt. % Li.

3. The aluminum alloy of claim 2, wherein the aluminum alloy comprises at least 0.01 wt. % Fe and at least 0.01 wt. % Si.

4. The aluminum alloy of claim 3, wherein the aluminum alloy comprises from 0.15-0.30 wt. % Cu.

5. A wrought product made from the aluminum alloy of claim 3, wherein the wrought product realizes a tensile yield strength of at least 32 ksi.

6. The wrought product of claim 5, wherein the wrought product realizes an elongation of at least 10%.

7. The wrought product of claim 5, wherein the wrought product realizes a rotating beam fatigue life of at least 1,000,000 cycles when tested in accordance with ISO1143, where the test specimen is unnotched (K.sub.t=1), and where the test conditions are R=−1 and the stress is alternating with a maximum of 25 ksi.

8. The wrought product of claim 5, wherein the wrought product realizes an average depth of attack of not greater than 100 micrometers when tested in accordance with ASTM G110, where the depth of attack is measured after 24 hours of immersion and at the 3T/4 location of the product.

9. The wrought product of any claim 5, wherein the wrought product comprises an anodized portion and a coated portion on the anodized portion, and wherein the coated portion of the wrought product realizes an L* color value of not greater than 40 L* when measured in accordance with ASTM E1164/E308, using a BYK Color Calibration Standard number of 1083053 (L*=94.89), and using a hand-held BYK-Gardner Spectro Guide 45/0 Spectrophotometer (or equivalent), and using an average of at least three L* measurements.

10. The wrought product of claim 9, wherein the coated portion realizes a gloss value of at least 550 when measured in accordance with ASTM D4039/D523 and using a hand-held gloss meter Elcometer 406L (or equivalent), using a BYK Gloss Standard number of 10071035 (93.5), and using an average of at least three gloss value measurements.

11. The wrought product of claim 9, wherein the coated portion realizes a surface hardness value of at least 7H when tested in accordance with ASTM D3363.

12. The wrought product of claim 9, wherein the coated portion is thermally stable as per GM standard GM9525P (1988).

13. The wrought product of claim 9, wherein the coated portion comprises a silicon-based coating.

14. The wrought product of claim 13, wherein the silicon-based coating is a siloxane based coating.

Description

DETAILED DESCRIPTION

Example 1

[0045] Four alloys were cast as industrial size ingots, the compositions of which are provided below.

TABLE-US-00001 TABLE 1 Composition of Ex. 1 Alloys (in wt. %) Alloy Si Mg Zn Mg/Zn Cu Mn Cr Fe Ti Note 1 0.09 3.03 2.49 1.22 0.24 0.58 0.05 0.10 0.02 Invention 2 0.09 3.48 3.03 1.15 0.16 0.40 — 0.10 0.02 Invention 3 1.08 0.6 0.51 1.18 1.17 0.14 0.18 0.10 0.02 Non-Invention  4* 0.75 1.12 0.21 5.33 0.38 0.14 0.23 0.18 0.01 Non-invention *Alloy 4 is per commonly-owned U.S. Patent No. 9,556,502.

[0046] After casting, the alloys were homogenized and cut into billets for forging. The billets were then die forged into wheels, during which the wheels were slowly cooled while traveling through the manufacturing facility. The forging exit temperature was approximately 740° F. (393° C.) and the quench rate was approximately 100° F. (37.8° C.) per minute, which is a relatively slow quench rate. In other words, the wheels were subjected to press-quenching. After the slow cooling, portions of the wheels were cold spun to make the final wheel products. The wheels were then artificial aged by heating to 385° F. (196.1° C.) and then holding for 2 hours at this temperature. Portions of the wheel receiving zero or insubstantial cold work (e.g., the disk face, the mounting flange, the cat ear) are accordingly in the T5 temper after the artificial aging. The portions of the wheel receiving cold work resulting in a change in mechanical properties (e.g., the rim) are in the T10 temper after the artificial aging. ANSI H35.1 (2009) defines these tempers, as per below. [0047] T5: Applies to products that are not cold worked after cooling from an elevated temperature shaping process, or in which the effect of cold work in flattening or straightening may not be recognized in mechanical property limits. [0048] T10: artificially aged. Applies to products that are cold worked to improve strength, or in which the effect of cold work in flattening or straightening may not be recognized in mechanical property limits. [0049] Note: different wheels have different geometries, so which portion(s) of a press-quenched wheel (if any) are in the T5 temper and/or the T10 temper should be determined on a case-by-case basis. [0050] Note: in aluminum working terms, “hot” and “cold” have more technical definitions than their common meaning. “Hot” working generally refers to working at a metal temperature high enough to avoid strain-hardening (work-hardening) as the metal is deformed. “Cold” working generally means working the metal at a temperature low enough for strain hardening to occur, even if the alloy would feel hot to human senses.”

[0051] Mechanical properties of the wheels were measured at various locations, the results of which are provided in Tables 2a-2b, below.

TABLE-US-00002 TABLE 2a Mechanical Properties of Ex. 1 Wheel Products Location of the wheel (Test Direction) Cat Ear (LT) Disk Face (L) TYS, UTS, Elong, TYS, UTS, Elong, Alloy ksi ksi % ksi ksi % 1 33.6 52.0 18.8 33.0 51.3 18.7 2 47.6 61.7 17.3 45.4 59.7 18.7 3 31.7 43.4 17.3 29.9 41.8 17.7 4 25.2 35.0 18.0 21.6 32.1 19.0

TABLE-US-00003 TABLE 2b Mechanical Properties of Ex. 1 Wheel Products Location of the wheel (Test Direction) Mount Face (L) Rim (L) TYS, UTS, Elong, TYS, UTS, Elong, Alloy ksi ksi % ksi ksi % 1 32.6 50.8 19.0 45.2 55.0 16.0 2 44.7 59.1 18.0 46.4 56.8 16.5 3 29.4 41.3 18.0 36.5 40.7 15.2 4 21.8 32.4 19.0 37.6 40.7 15.5
As shown, despite the slow quench, the invention alloys realized high strength, and with invention alloy 2 realizing extremely high strength.

[0052] The fatigue properties of the alloys were also tested by subjecting the wheels to rotating beam fatigue testing in accordance with ISO1143. The R value for the fatigue testing was R=−1, the specimen was unnotched (K.sub.t=1), and the stress was an alternating stress with a max stress of 25 ksi. The fatigue specimens were extracted from the disk face location of the wheels. The fatigue results are provided in Table 3, below.

TABLE-US-00004 TABLE 3 Fatigue Properties of Ex. 1 Wheel Products Cycles to Cycles to Cycles to Failure Failure Failure Alloy (Sample 1) (Sample 1) (Sample 1) Average 1 1.71E+06 2.11E+06 2.38E+06 2,066,667 2 5.00+E6  .sup.   4.05E+06 4.95E+06 4,500,000 3 6.52E+05 1.50E+06 3.09E+05 820,333 4 1.22E+05 9.95E+04 1.15E+05 112,166
As shown, the invention alloys realized much better fatigue life as compared to the non-invention alloys. Indeed, alloy 2 did not fail even after 4 million cycles of testing.

[0053] The corrosion resistance properties of the alloys were also tested in accordance with ASTM G110. The results are provided in Table 4, below. As shown, the invention alloys realize good corrosion resistance properties.

TABLE-US-00005 TABLE 4 G110 Corrosion Properties of Alloys G110- Depth of Attack - 24 hours (micrometers) 3T/4 3T/4 T/4 T/4 Corrosion Alloy (ave.) (max.) (ave.) (max.) mode 1 18.9 24.1 17.8 40.0 Pit 2 13.9 18.2 12.0 13.1 Pit 3 91.4 138.8 79.0 92.2 Pit, IGC, ISGC 4 96.5 140.5 78.8 100.8 Pit, IGC, ISGC

Example 2—Testing of Surface Appearance

[0054] Example alloys 2 and 4 were tested for surface appearance properties. Specifically, wheels made from alloys 2 and 4 were phosphoric acid anodized and then coated with a siloxane based polymer in accordance with the conditions set forth in U.S. Pat. No. 6,440,290, i.e. as per Main Steps 1-4, below. The '290 patent is associated with the current assignee's DURA-BRIGHT process and products. [0055] Main Step 1. A single chemical treatment, the composition and operating parameters of which are adjusted depending on whether the preferred products to be treated are made from an Al—Mg, Al—Mg—Si or an Al—Si—Mg alloy. This chemical treatment step imparts brightness to the aluminum being treated while yielding a chemically clean outer surface ready for subsequent processing. This step replaces previous multi-step buffing and chemical cleaning operations. On a preferred basis, this chemical brightening step uses an electrolyte with a nitric acid content between about 0.05 to 2.7% by weight. It has been observed that beyond 2.7 wt % nitric acid, a desired level of brightness for Al—Mg—Si—Cu alloys cannot be achieved. On a preferred basis, the electrolyte for this step is phosphoric acid-based, alone or in combination with some sulfuric acid added thereto, and a balance of water. Preferred chemical brightening conditions for this step are phosphoric acid-based with a specific gravity of at least about 1.65, when measured at 80° F. More preferably, specific gravities for this first main method step should range between about 1.69 and 1.73 at the aforesaid temperature. The nitric acid additive for such chemical brightening should be adjusted to minimize a dissolution of constituent and dispersoid phases on certain Al—Mg—Si—Cu alloy products. Such nitric acid concentrations dictate the uniformity of localized chemical attacks between Mg.sub.2Si and matrix phases on these 6000 Series Al alloys. As a result, end product brightness is positively affected in both the process electrolyte as well as during transfer from process electrolyte to the first rinsing substep. On a preferred basis, the nitric acid concentrations of main method step 1 should be about 2.7 wt. % or less, with more preferred additions of HNO.sub.3 to that bath ranging between about 1.2 and 2.2 wt. %. [0056] Main Step 2. The second main step is to deoxidize the surface layer of said aluminum product by exposure to a bath containing nitric acid, preferably in a 1:1 dilution from concentrated. This necessary step ‘prep's’ the surface for the oxide modification and siloxane coating steps that follow. [0057] Main Step 3. The third main step of this invention is a surface oxide modification designed to induce porosity in the surface's outer oxide film layer. The chemical and physical properties resulting from this modification will have no detrimental effect on end product (or substrate) brightness. Like main step 1, the particulars of this oxide modification step can be chemically adjusted for Al—Mg—Si versus Al—Si—Mg alloys using an oxidizing environment induced by gas or liquid in conjunction with an electromotive potential. Surface chemistry and topography of this oxide film are critical to maintaining image clarity and adhesion of a subsequently applied polymeric coating. One preferred surface chemistry for this step consists of a mixture of aluminum oxide and aluminum phosphate with crosslinked pore depths ranging from about 0.1 to 0.1 micrometers, more preferably less than about 0.05 micrometers. That is, subsequent to deoxidation, an oxide modification step is performed that is intended to produce an aluminum phosphate-film with the morphological and chemical characteristics necessary to accept bonding with an inorganic polymeric silicate coating. This oxide modification step should deposit a thickness coating of about 1000 angstroms or less, more preferably between about 75 and 200 angstroms thick. If applied electrochemically, this can be carried out in a bath containing about 2 to 15% by volume phosphoric acid. [0058] Main Step 4. Fourthly, an abrasion resistant, siloxane-based layer is applied to the aluminum product, said layer reacting with the underlying porous oxide film, from above step 3, to form a chemically and physically stable bond therewith. Preferably, this siloxane coating is sprayed onto the substrate using conventional techniques in which air content of the sprayed mixture is minimized (or kept close to zero). To optimize transfer onto the aluminum part viscosity and volatility of this applied liquid coating may be adjusted with minor amounts of butanol being added thereto. That is, siloxane-based chemistries are applied to the oxide-modified layers from Main Step 3, above. Both initial and long term durability of such treated products depend on the proper surface activation of these metals, followed by a siloxane-based polymerization. Abrasion resistance of the resultant product is determined by the relative degree of crosslinking for the siloxane chemicals being used, i.e. the higher their crosslinking abilities, the lower the resultant film flexibility will be. On the other hand, lower levels of siloxane crosslinking will increase the availability of functional groups to bond with modified, underlying Al surfaces thereby enhancing the initial adhesion strengths. Under the latter conditions, however, coating thicknesses will increase and abrasion resistance decreases leading to lower clarity and durability properties, respectively. Suitable siloxane compositions for use in main step 4 include those sold commercially by SDC Coatings Inc. under their Silvue® brand. Other suitable manufacturers of siloxane coatings include Ameron International Inc., and PPG Industries, Inc. It is preferred that such product polymerizations occur at ambient pressure for minimalizing the impact, if any, to metal surface microstructure. For any given aluminum alloy composition and product form, the compatibility of main step 3 surface treatments with main step 4 siloxane polymerizations will dictate final performance attributes. Due to the stringent surface property requirements needed to achieve highly crosslinked siloxane chemical adhesion atop metal surfaces, highly controlled surface preparations and polymerization under vacuum conditions are typically used. Most preferably, siloxane chemistries are applied using finely dispersed droplets rather than ionization in a vacuum. Control and dispersion of these droplets via an airless spray atomization minimizes exposure with air from conventional paint spraying methods and achieves a preferred breakdown of siloxane dispersions in the solvent. The end result is a thin, highly transparent, “orange peel”-free durable coating.

[0059] After steps 1-4, above, were properly performed, the color and gloss of the coated surfaces were tested. Color was tested per ASTM E1164/E308 and using a hand-held BYK-Gardner Spectro Guide 45/0 Spectrophotometer (or equivalent). The BYK Color Calibration Standard is number 1083053 (L*=94.89). Gloss is tested per ASTM D4039/D523 and using a hand-held gloss meter Elcometer 406L (or equivalent). The BYK Gloss Standard is number 10071035 (93.5). The results are provided below (average of three measurements).

TABLE-US-00006 TABLE 5 Surface Appearance Results Alloy Color (L*) Gloss 2 27.3 727 4 34 640

[0060] As shown, new alloy 2 outperforms alloy 4 in terms of both color and gloss quality, realizing a color (L*) value of well under the maximum limit of 40, and also realizing a gloss value of 727, well above the minimum limit of 550.

[0061] The surface hardness of coated alloy wheel 2 was also tested in accordance with ASTM D3363. Alloy 2 realized a pencil hardness rating of 9H, which is the highest possible rating under the ASTM standard.

[0062] The thermal stability of the coated wheel made from alloy 2 was also tested in accordance with GM standard GM9525P (1988). The wheel passed the test, realizing no peeling of the coated surface.

[0063] While the above appearance properties were achieved using a phosphoric acid anodizing, it is believed that similar appearance properties may be realized using other anodizing solutions (e.g., using sulfuric, chromic, or other conventionally known anodizing acids/solutions) and/or anodizing processes (e.g., conventional Type II or Type II anodizing). Further, while siloxane based coatings are noted as being used above, it is believed similar properties may be realized with other silicon-based coatings or even non-silicon based coatings. Further, while the example wheel products were in both the T5 and T10 condition (because some portions were cold worked whereas others were not), it is believed similar properties may be realized by wheel products in the T6 temper, such as when the wheel is forged and then spun prior to solution heat treatment, after which the spun wheel product is then subject to a conventional solution heat and quench, following by artificial aging.

[0064] While various embodiments of the present disclosure have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.