WO2020117771A1

WO2020117771A1 - Aluminum extrusion alloy

Info

Publication number: WO2020117771A1
Application number: PCT/US2019/064188
Authority: WO
Inventors: Jerome FOURMANN; Nicholas C. Parson
Original assignee: Rio Tinto Alcan International Limited
Priority date: 2018-12-03
Filing date: 2019-12-03
Publication date: 2020-06-11
Also published as: MX2021006502A; CA3121249A1; US20220025489A1; JP7679295B2; EP3891312A4; EP3891312A1; JP2022513644A

Abstract

An aluminum alloy includes Si and Mg in amounts (wt.%) within a quadrilateral defined by the following coordinates on an Mg/Si plot: I: 1.15 Si, 0.70 Mg, II: 0.95 Si, 0.55 Mg; III: 0.75 Si, 0.65 Mg; and IV: 0.95 Si, 0.85 Mg. The alloy also includes, in weight percent: Mn 0.40 – 0.80 Fe 0.25 max Cr 0.05 – 0.18 Cu 0.30 – 0.90 Ti 0.05 max Zr 0.03 max Zn 0.03 max B 0.01 max with the remainder of the alloy being aluminum and unavoidable impurities in amounts of up to 0.05 wt.% each and 0.15 wt.% total.

Description

ALUMINUM EXTRUSION ALLOY

CROSS-REFERENCE TO RELATED APPLICATION

[01] This application claims priority to, and the benefit of, U.S. Provisional Application No. 62/774,661, filed December 3, 2018, which prior application is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[02] This disclosure relates to aluminum alloys suitable for use in extrusion, and more specifically in one aspect to Al-Mg-Si-Cu-Mn-Cr extrusion alloys having high strength and ductility.

BACKGROUND

[03] Aluminum extrusion alloys are often used for automotive applications, and higher strength extras! on alloys having yield strengths of at least 350 MPa are sometimes desired or needed for this purpose. A number of existing commercial alloys are capable of this strength level, such as AA6066 and AA6056, but these alloys exhibit decreased extrudability compared to standard extrusion alloys. Ductility and crush performance can also be an issue in such higher strength alloys. Thus, there is a need for an aluminum extrusion alloy capable of consistently achieving a yield strength of 350 MPa or greater, with good extrudability and ductility. In order to ensure that an alloy in commercial production consistently meets a minimum yield strength, it is desirable that the average or typical yield strength value should significantly exceed the minimum target, such as by at least 20 MPa, to account for variations in strength from sample to sample. For example, to ensure that a targeted minimum strength of 350 MPa is consistently met, an average yield strength of 370 MPa or more would be desired.

[04] The present disclosure is provided to address this need and other needs in existing aluminum extrusion alloys A full discussion of the features and advantages of the present invention is deferred to the following detailed description, which proceeds with reference to the accompanying drawings. BRIEF SUMMARY

[05] Aspects of the disclosure relate to an aluminum extrusion alloy that includes Si and Mg in amounts within a quadrilateral defined by the following coordinates on an Mg/Si plot, in weight percent:

I 1.15 Si, 0.70 Mg

II 0.95 Si, 0.55 Mg

IP 0.75 Si, 0.65 Mg

IV 0.95 Si, 0.85 Mg

wherein the alloy further comprises, in weight percent:

Mn 0.40 - 0.80

Fe 0.25 max

Cr 0.05 - 0.18

Cu 0.30 - 0.90

Ti 0.05 max

Zr 0.03 max

Zn 0.03 max

B 0.01 max

with the remainder of the alloy being aluminum and unavoidable impurities in amounts of up to 0.05 wt.% each and 0.15 wt.% total.

[06] According to one aspect, the Mg and Si are present in an Mg/Si ratio of at least 0.69 and/or no more than 0.88.

[07] According to another aspect, the alloy includes excess Mg, and in one embodiment, up to 0.40 wt.% excess Mg as defined herein.

[08] According to a further aspect, the alloy, after homogenization, extrusion, and artificial ageing, has a predominantly non-reerystallized microstructure.

[09] According to yet another aspect, after homogenization, extrusion, and artificial ageing, has a yield strength of at least 350 MPa and a tensile elongation of at least 8%. The alloy may have a yield strength of at least 370 MPa in one embodiment. [10] According to a still further aspect, the alloy includes Mg in an amount of 0.60 - 0.80 wt.% and Si in an amount of 0.85 - 1.10 wt.%. In one embodiment, the Mg content may be 0 70 - 0.80 wt.% and the Si content may be 0.85 - 0.95 wt.%

[11] According to yet another aspect, the Si and Mg in amounts are within a quadrilateral defined by the following coordinates on the Mg/Si plot, in weight percent:

I 1.15 Si, 0.70 Mg

II 0.95 Si, 0.55 Mg

IIG : 0.80 Si, 0.65 Mg

IV’: 0.95 Si, 0.80 Mg.

[12] Additional aspects of the disclosure relate to an aluminum extrusion alloy that includes, in weight percent:

Mg 0.60 - 0.80

Si 0.85 - 1.10

Mn 0.40 - 0 80

Fe 0.25 max

Cr 0.05 - 0.18

Cu 0.30 - 0.90

Ti 0 05 max

Zr 0.03 max

Zn 0.03 max

B 0.01 max

with the remainder of the alloy being aluminum and unavoidable impurities in amounts of up to 0.05 each and 0.15 total. The alloy may include any other aspects discussed above herein.

[13] Further aspects of the disclosure relate to an extruded product that is at least partially formed of an aluminum alloy as described herein.

[14] Still further aspects of the disclosure relate to a method that includes casting or otherwise forming a billet of an aluminum alloy as described herein, e.g., using direct chill casting or other continuous casting technique, then homogenizing the billet and extruding the homogenized billet to form an extruded product. The homogenization may be conducted by heating the billet at a temperature of 540-58G°C for 2-10 hours, and then cooling the billets at a cooling rate of 300°C/hour or more after homogenization.

[15] Other features and advantages of the disclosure will be apparent from the following description taken in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[16] To allow for a more full understanding of the present disclosure, it will now be described by way of example, with reference to the accompanying drawings in which:

[17] FIG 1 illustrates magnesium and silicon content of embodiments of an aluminum alloy according to aspects of the disclosure;

[18] FIG. 2 illustrates a plot of crush rating and fracture strain vs. yield strength for several alloys tested in Examples 1 and 2 herein;

[19] FIG. 3 illustrates a plot of mean crush force vs. yield strength for several alloys tested in Examples 1 and 2 herein;

[20] FIG. 4 illustrates a plot of ram pressure vs. yield strength for several alloys tested in Example 2 herein; and

[21] FIG. 5 illustrates magnesium and silicon content of embodiments of an aluminum alloy according to aspects of the disclosure, as well as example compositions tested in Example 5 herein.

DETAILED DESCRIPTION

[22] While this invention is susceptible of embodiments in many different forms, there are shown in the drawings and will herein be described in detail example embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated. It is to be understood that other specific arrangements features may be utilized and modifications may be made without departing from the scope of the present invention.

[23] Aspects of the disclosure relate to an aluminum alloy that is useful for extrusion applications, having various alloying elements including Mg, Si, Fe, Mn, Cu, and Cr. An alloy as described herein may also be useful in forging applications, and may produce beneficial properties in such an application. All composition percentages listed herein are in weight percent unless otherwise indicated.

[24] In one embodiment, the alloy may include magnesium in an amount of 0 60 - 0.80 wt.%, or 0.6 - 0.8 wt.%, and silicon in an amount of 0.85 - 1.10 wt.%. The Mg and Si in this composition may also be present in an Mg/Si ratio (wt.%) of at least 0.69 in one embodiment. The Mg/Si ratio may additionally or alternately have an upper limit of 0.88 in one embodiment or 0.85 in another embodiment. Alloys with Mg/Si ratios that are too high can be detrimental to extrudability in amounts, and alloys with Mg/Si ratios above these amounts may exhibit unsatisfactory extrudability. In another embodiment, the alloy may include magnesium in a range of 0.70 - 0.80 wt.% and silicon in a range of 0.85 - 0.95 wt.%.

[25] In another embodiment, the alloy may include magnesium and silicon in amounts defined within a quadrilateral defined by the following coordinates on a Mg/Si plot, as shown in FIG. 1 :

I: 1.15 Si, 0.70 Mg

II: 0.95 Si, 0.55 Mg

III: 0.75 Si, 0.65 Mg

IV: 0.95 Si, 0.85 Mg

[26] The alloy in a further embodiment may include magnesium and silicon in amounts defined within a quadrilateral defined by the following coordinates on an Mg/Si plot, as shown in FIG. 1 : I: 1.15 Si, 0.70 Mg

II: 0.95 Si, 0.55 Mg

IIP : 0.80 Si, 0.65 Mg

IV’: 0.95 Si, 0.80 Mg

[27] In any of the embodiments herein, the alloy may include at least some excess magnesium (i.e., excess Mg > 0) as defined by the equation below:

Excess Mg = Mg - (Si - (Mn+Fe+Cr)/3)/1.16 (all values in wt%)

[28] The alloy may include up to 0.40 wt.% excess magnesium in one embodiment, and up to 0 35 wt.% excess magnesium in another embodiment. Excess Mg can be detrimental to extrudabiJity in amounts that are too high, and alloys with excess Mg above these amounts may exhibit unsatisfactory extrudability.

[29] The alloy may further contain the following elements, in wt.%:

Mn 0.40 - 0 80

Fe 0.25 max

Cr 0.05 - 0 18 Cu 0.30 - 0.90

Ti 0 05 max

Zr 0.03 max

Zn 0.03 max with the remainder of the alloy being aluminum and unavoidable impurities, which may be present in amounts of up to 0.05 wt.% each and 0 15 wt.% total. In one embodiment, the alloy may include additional elements not listed. [30] Silicon can combine with iron, manganese, and/or chromium in intermetallic phases in the alloy. Additionally, manganese and chromium in sufficient amounts can form dispersoid particles that inhibit grain recrystallization after extrusion. The iron content of the alloy in one embodiment is 0.25 wt% max. In another embodiment, the iron content of the alloy may be 0.15 - 0.25 wt.%. The chromium content of the alloy in one embodiment is 0.05 - 0.18 wt.%. In another embodiment, the chromium content of the alloy may be 0.05 - 0.15 wt.%. The manganese content of the alloy in one embodiment is 0 40 - 0.80 wt.%, but may alternately be 0 4 - 0.8 wt.%. In another embodiment, the manganese content of the alloy may be 0.40 - 0 55 wt.%.

[31] Copper can increase strength of the alloy. The copper content of the alloy in the embodiment listed above is 0 30 - 0.90 wt%, but may alternately be 0.3 - 0.9 wt.%. In other embodiments, the copper content of the alloy may be 0.30 - 0.80 wt.%, 0.60 - 0.80 wt.%, or 0 60 - 0 90 wt.%.

[32] Titanium is added as a grain refiner in one embodiment, and may be added along with boron in the form of TiB rod (e.g., 5% Ti, 1% B). Accordingly, the alloy may also include up to 0.01% or up to 0.005% boron in one embodiment.

[33] Alloys according to aspects and embodiments herein may be prepared by forming into billets through direct chill casting or other continuous casting method in one embodiment, and then homogenizing the billets. Homogenization may be performed, for example, at 54Q~580°C for 2-10 hours, and then cooling the billets at 300°C/hour or more, e.g., 300-600°C/hour, after homogenization. It is understood that these cooling rates may be measured over a portion of the cooling range, and not throughout the entire cooling of the billet (i .e., homogenization temperature to ambient temperature). For example, in one embodiment, the relevant cooling rate may be measured between the temperatures of 500°C and 200°C during cooling. The billets may then be extruded into an extrusion profile or extruded product, which may include at least one concave surface, at least one convex surface, at least one angled comer, and/or at least one internal cavity in some uses. Extrusion may be performed in one embodiment by preheating to 470-520°C prior to extrusion and water quenching at the press exit, e.g., by water sprays or a standing wave water box, which may achieve cooling at about 50-1000°C/sec. The extruded product may be subjected to artificial ageing after extrusion, such as heating for 5-16 hours at 160-185°C. It is understood that other processing may be used in other embodiments, including post-extrusion processing to the extruded product to achieve desired properties, geometry, etc.

[34] The extruded product produced using the alloys and processing techniques described herein may have a post-extrusion grain structure that is predominantly fibrous or non recrystal lized in one embodiment. This predominantly fibrous microstructure may have a microstructure that is at least 50% unrecrystallized in one embodiment, or at least 75% unreerystailized in another embodiment, which may be over a majority of the length of the extruded profile or over the entire length. A non-recrystallized grain structure may improve the yield strength of the alloy after extrusion. In one embodiment, an alloy as described herein may achieve a yield strength of at least 350 MPa or at least 360 MPa, with a tensile elongation of at least 8%, at least 9%, or at least 10%, after extrusion and artificial ageing.

[35] Below are several examples illustrating the beneficial properties and advantageous performance of alloys according to aspects of the disclosure, as well as comparative alloys.

[36] EXAMPLE 1

[37] The alloy compositions listed in Table 1, representing existing commercial high strength AA 6XXX alloys, were direct chill cast as 101.6 mm diameter ingots, and a 5% Ti - 1% B grain refiner was added prior to casting to ensure a fine as-cast grain size.

Table 1 : Commercial Alloy Compositions

[38] The ingots w'ere cut into 400 mm billet lengths and homogenized. The billets of AA61 11 and AA6056 were homogenized for 2 hours at 560°C, and the AA6066 billet was homogenized for 4 hours at 545°C. The billets were cooled at 400°C/hr after homogenization.

[39] The billets were extruded into a 40x30x2 mm hollow profile with a 5 mm external comer radius using a billet temperature of 475°C and a ram speed of 4-6 mm/s. The ram speed was varied to find the maximum speed attainable before surface cracking occurred. This maximum ram speed is reported in Table 2. The extrusion ratio w¾s 32/1, such that corresponding exit speeds ranged from 8~12m/rain. The extrusion was water quenched at a rate of ~1000°C/sec using a standing wave water quench unit positioned about 2.5m from the extrusion die. The extrusions were floor aged at room temperature for 24 hours before artificial ageing for 8hrs/175°C.

[40] Crush tests were performed by axially crushing a 150 mm length to 30 mm at a cross head speed of 20 rnm/s. The load displacement curve was recorded and the mean crush force (MCF) was calculated using an averaging technique. The extent of cracking (crush rating CR) during the crush test was assessed on a scale of 1 to 9, where 1 represented a crack free sample and 9 represented full disintegration. Longitudinal tensile testing was performed, the area of the final fracture was measured, and the true fracture strain was calculated as er = -Ln (final area/initial area). The true fracture strain (er) has been shown to be a good measurement of ductility at high plastic strains. The mechanical property and crush testing results are also reported in Table 2, where RX signifies a fully recrystallized grain structure and F signifies a predominantly fibrous grain structure. Some of these results are also depicted graphically in FIGS. 2-3.

Table 2: Mechanical Properties

[41] The AA6066 alloy exhibited the lowest extrusion speed, followed by the AA6056 alloy. The AA61 11 alloy had the highest maximum ram speed, and was the most extrudable of the three alloys. AA61 11, which is widely used as an automotive sheet alloy, resulted in a fully recry stall! zed grain structure and did not meet the 350 MPa minimum yield strength target. Both the AA6056 and AA6066 alloys exhibited yield strengths in excess of the 350MPa target, along with a predominantly fibrous or non-recrystallized grain structure. However, the higher strengths of these alloys did not translate into increased energy absorption, and AA6056 and AA6066 both performed poorly in crush testing. In particular, the AA6066 alloy experienced premature onset of cracking in the crush test and had a low fracture strain. [42] EXAMPLE 2

[43] The alloys listed in Table 3 were direct chill cast as 101.6 rnm diameter ingots and cut into 400 mm billet lengths, and a 5% Ti - 1% B grain refiner was added prior to casting to ensure a fine as-cast grain size.

Table 3 : Alloy Compositions

[44] The billets were homogenized for 2 hours at 550°C and cooled at 400°C/hour after homogenization. The billets were extruded into a 40x30x2 mm hollow profile using a billet temperature of 500°C and a fixed ram speed of 5 mm/s. The extrusion was water quenched at a rate of- 1000°C/sec using a standing wave water quench unit positioned about 2,5m from the extrusion die. The extrusions were floor aged at room temperature for 24 hours before artificial ageing for 8 hours at 175°C. Tensile and crush testing was performed, the extrusion hydraulic pressure was monitored and the maximum (breakthrough) pressure value and the value at 50% of the ram stroke were extracted. The percentage difference in breakthrough pressure compared to alloy A (DR) was calculated to give an indication of the relative extrudability. The increase in yield strength per each % increase in extrusion pressure compared to alloy A was also calculated to assess the strengthening efficiency as compared to the effect on extrudability. The test results are summarized in Table 4, where RX signifies a fully recrystallized grain structure and F signifies a predominantly fibrous grain structure. Some of these results are also depicted graphically in FIGS. 2-4

Table 4: Mechanical Properties

[45] Alloy A, which is used for comparative purposes, is based on an automotive grade AA6082, gave good ductility and a good crush rating, but only achieved a yield strength of 312 MPa. The alloy contained additions of Mn and Cr to form submicron dispersoid particles during homogenization and this resulted in a predominantly fibrous/non-recrystallized grain structure after extrusion. Alloy B, with a V addition relative to Alloy A, exhibited similar strength and ductility with a small (1 grade) improvement in crush rating. Alloy C, with an addition of 0.32% Cu relative to Alloy A, exhibited a yield strength in excess of the 350 MPa target with some deterioration in ductility as measured by the fracture strain and crush rating. Alloy D, with an addition of 0.61% Cu relative to Alloy A, exhibited an excellent yield strength of 379MPa with only slightly lower fracture strain and inferior crush rating to Alloy C. Alloy E, with an addition of 0.30% Cu relative to Alloy A, but no addition of Cr and only 0.07% Mn, resulted in a recrystallized grain structure. While Alloy E only exhibited a yield strength of 346 MPa, it also gave the lowest fracture strain and highest (worst) crush rating of 9, representing full disintegration. Finally, Alloy F, which was similar to alloy C but with the Mn content increased to 0.77, gave slightly lower strength than alloy C, nearly meeting the 350 MPa target, but a significantly better crush rating.

[46] The fracture strain and crush rating results for Examples 1 and 2 are plotted in FIG. 2 as a function of the yield strength. From examination of this plot, it is apparent that Alloys C and D offer a yield strength in excess of 350 MPa and reasonable ductility in terms of crush rating and fracture strain. Although the existing commercial alloys AA6066 and AA6056 are capable of higher strengths, this increased strength is accompanied by a significant deterioration in fracture strain and crush rating relative to Alloys C and D. The results for the other alloy variants would suggest that a predominantly fibrous (non-recrystallized) grain structure is preferred, and that reduced levels of Mn and the absence of Cr, as in the case of Alloy E, are undesirable. The improved crush rating and reasonably high yield strength for Alloy F suggests that increasing the Mn level to about 0.8% in addition to the Cr addition could also be beneficial.

[47] FIG. 3 shows a similar plot for MCF vs. yield strength for the alloys in Examples 1 and 2. In general, the MCF increases in line with the yield strength, with the exception of Alloys E and AA6066, due to their reduced ductility and premature failure in the crush test. Similar conclusions can be drawn from the data in FIGS. 2 and 3.

[48] FIG. 4 shows the extrusion pressure results for the breakthrough pressure (upper curve) and the pressure at mid stroke (lower curve), again plotted against the yield strength to give an indication of the penalty in extrudability incurred by increasing the alloy strength. Adding extra solute to an alloy to gain extra strength from artificial ageing would be expected to increase the high temperature flow stress, making the alloy more difficult to extrude in general, the higher the extrusion pressure of an alloy, the lower the maximum extrusion speed that can be achieved for a given billet temperature. Using Alloy A as the baseline, FIG. 4 indicates that Alloy E was the only variant to exhibit lower extrusion pressure than the base alloy. However, as described above, this also corresponded to significantly inferior ductility. Alloy B, containing the V addition, required ~ 5% higher breakthrough pressure than Alloy A, with no corresponding increase in yield strength. Alloys C and D required extrusion pressure increases of 1.8 and 5.9% respectively for useful yield strength increases of 49 and 67 MPa relative to Alloy A. Alloy F required a 6.9% increase in breakthrough pressure for a yield strength gain of 36 MPa relative to Alloy A When the yield strength increase per % increase in breakthrough pressure values are compared in Table 4, it is dear that alloys C and D containing additions of about 0.3 and 0.6 Cu are the most efficient in terms of achieving the target strength level with minimum loss of extrudability.

[49] EXAMPLE 3

[50] The alloy compositions G and H shown in Table 5 w^?ere direct chill cast as 228 mm diameter ingots, cut into billets, homogenized for 2 hours at 560°C, and cooled at 450°C/hour after homogenization. Five billets of each alloy w^?ere extruded on a commercial extrusion press into a two-cavity bumper profile with wall thicknesses varying between 2.6 and 3.6 mm. A billet preheat temperature of 500°C was used with a ram speed of 3 mm/s. The profile was spray water quenched and artificially aged for 8 hours at 175°C. Alloys G and H contained Cu, Mn, and Cr contents similar to those of Alloy D from Example 2, but the Mg and Si contents of these alloys were increased relative to Alloy D. Tensile testing was conducted on the top and bottom of the profile, and the results are shown in Table 5.

Table 5: Alloy Compositions and Mechanical Properties

[51] The grain structure was checked by optical metallography, and all extrusions had a predominantly fibrous/non-recrystallized grain structure. The strength of both Alloys G and H vailed between the top and bottom locations, most likely due to variations in quench rate associated with the spray quench settings. Both alloys achieved yield strengths of 360 MPa or greater for the bottom locations with the lower quench rate and near or exceeding 380 MPa at the faster quenched top location.

EXAMPLE 4

[53] Alloy I, shown in Table 6, was direct chill cast as 101.6 mm ingots and cut into billets. The billets were homogenized for 2 hours at 560°C and cooled at 450°C/hour after homogenization, and were then extruded into a 50 x 2.5mm strip using a billet temperature of 500°C and a ram speed of 5 mm/s. The extrusion was water quenched at a rate of 1000°C/sec at the press exit and then artificially aged for 8 hours at 175°C. After this treatment, Alloy I achieved a yield strength of 391 MPa, an ultimate tensile strength of 419 MPa, and 12.7% elongation in tensile testing.

Table 6: Alloy Composition

[54] Alloy J, shown in Table 7, was direct chill cast as 254 mm diameter billet and homogenized for 3 hours at 560°C and cooled at 400°C/hour after homogenization.

Table 7 : Alloy Composition

[55] This billet was extruded on a commercial press into a bumper profile with an extrusion ratio of 50.1 and wail thicknesses from 2.5 to 5mm using a billet temperature of 490°C and an exit speed of 8m/min. The profile was spray quenched at the press exit. After artificial ageing for 8 hours at 175°C, Alloy J achieved a yield strength of 395 MPa, an ultimate tensile strength of 421 9 MPa, and an elongation of 10 4%

[56] EXAMPLE 5

[57] The alloy compositions listed in Table 8 were direct chill cast as 101.6mm ingots and cut into 200mm billet lengths. The billets were grain refined using a 5%Ti-l%B grain refiner added prior to casting. The billets were homogenized for 3 hours at 560°C and cooled at 400°C/hour, with the exception of alloy M, which had a lower equilibrium solidus and as a result was homogenized for 3 hours at 545°C to avoid melting, followed by cooling at 400°C/hour. Groups of 6 billets of each alloy were extruded into 3 x 42mm profiles with sharp comers, using a billet temperature of 480°C. The ram speed for each group was increased incrementally on successive billets from 4mm/s to 9mm/s until speed cracking was observed at the comers, and, based on this observation, the maximum extrusion speed (Vt) without tearing was established. The extrusions were water quenched at the press exit using a standing wave water quench unit giving a quench rate of ~ 1 G00°C/sec. The maximum breakthrough pressure was recorded during extrusion. Lengths of extrusion were then aged for 8 hours at 175°C and tensile testing was performed. Table 8 presents the results for each alloy in terms of tearing speed (Vt), yield strength (YS), ultimate tensile strength (UTS), breakthrough pressure (Pmax). FIG. 5 illustrates the Mg and Si compositions of Alloys G-M in Table 6 as compared to the Mg/Si plots I-IV and I-IV’ as shown in FIG. 1 and the ranges of 0.60 - 0.80 wt.% Mg and 0 85 - 1.10 wt.% Si described in the specification. As shown in FIG 5, Alloys G, I, I, and J are within these ranges, and Alloys K, L, and M are outside these ranges.

Table 8: Alloy Compositions and Test Results

[58] Alloys G, H, I and J all achieved yield strength levels in excess of 370 MPa, meeting and comfortably exceeding the target strength of 350 MPa. Alloys H and J have higher Si contents, and these alloys exhibited significantly lower tearing speeds than alloys G and I Alloy I achieved the best combination of high strength and high extrusion speed of the alloys tested in this Example. Table 8 shows the % breakthrough pressure increase or decrease (DR%) compared to Alloy I. Extrusion pressure values are not shown for alloys J and M, as these alloys could not be extruded at comparable speeds to the other alloys.

[59] Alloys K, L, and M have compositions outside the Mg/Si plot I- IV as shown in FIG. 1, and these alloys all exhibited lower yield strengths than Alloys G, H, I, and J that fall within the Mg/Si plot I-IV. Alloy K has a lower Si content such that the composition is outside the Mg/Si plot I-IV as shown in FIG 1 , and this al loy achieved a yield strength of only 352 MPa. The yield strength of Alloy K is insufficiently in excess of the target strength of 350 MPa to ensure that the target strength is consistently met in a production alloy, indicating a Si content higher than 0.72 wt.% achieves superior results. Alloy M has the highest silicon content such that the composition is outside the Mg/Si plot I-IV as shown in FIG. 1. Alloy M exhibited the lowest tearing speed, indicating that Alloy M is inferior for extaision. Additionally, Alloy M exceeded the target strength of 350 MPa by only lOMPa, and the yield strength of Alloy M is insufficiently in excess of the target strength of 350 MPa to ensure that the target strength is consistently met in a production alloy. The loss in extrudabiiity and strength in Alloy M compared to Alloys G, H, I and J indicate that a lower silicon content than 1.14 wt.% achieves superior results. Alloy L has a high Mg content such that the composition is outside the Mg/Si plot I-IV as shown in FIG. 1 . Alloy L exhibited generally acceptable strength and tearing speed. However, Alloy L still exhibited lower strength than Alloys G, H, I, and J, in addition to higher extrusion pressure (and therefore inferior extrudability) compared to Alloys G, H and I. Thus, under commercial extrusion conditions, the extrusion speed of Alloy L could he further restricted by the need to increase the billet temperature to reduce extrusion pressure. Alloy L therefore represents a combination of Mg and Si that exhibits an inferior combination of strength and extrudability compared to alloys that are within the Mg/Si plot I-IV as shown in FIG. 1 (e .. Alloys G, H, and I).

[60] Based on the strength and extrudability performance of alloys G, H, I, and J in this test, it has been demonstrated that the ranges of Mg and Si in the Mg/Si plot I-IV as shown in FIG. 1 and the ranges of 0 60 - 0 80 wt.% Mg and 0 85 - 1.10 wt.% Si described in the specification can provide yield strength levels comfortably in excess of the target of 35QMPa, with good extrudability. These testing results also establish that lower silicon contents do not provide adequate strength and higher silicon contents provide inferior strength and inferior extrudability. These testing results also establish that higher Mg contents result in an increase in extrusion pressure and inferior extrudability, with slightly inferior strength. The testing results further establish that the use of Mg and Si in ranges of 0 70 - 0 80 wt.% Mg and 0.85 - 0.95 wt.% Si achieve a particularly advantageous combination of strength and extrudability.

[61] Several alternative embodiments and examples have been described and illustrated herein. A person of ordinary skill in the art would appreciate the features of the individual embodiments, and the possible combinations and variations of the components. A person of ordinary skill in the art would further appreciate that any of the embodiments could be provided in any combination with the other embodiments disclosed herein. It is understood that the invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. Accordingly, while the specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention and the scope of protection is only limited by the scope of the accompanying claims.

Claims

CLAIMS What is claimed is:

1. An aluminum alloy comprising Si and Mg in amounts within a quadrilateral defined by the following coordinates on an Mg/Si plot, in weight percent:

I 1.15 Si, 0.70 Mg

II 0.95 Si, 0.55 Mg

III 0.75 Si, 0.65 Mg

IV 0.95 Si, 0.85 Mg

wherein the alloy further comprises, in weight percent:

Mn 0.40 - 0 80

Fe 0.25 max

Cr 0.05 - 0.18

Cu 0.30 - 0.90

Ti 0 05 max

Zr 0.03 max

Zn 0.03 max

B 0.01 max

2. The alloy of claim 1, wherein the Mg and Si are present in an Mg/Si ratio of no more than 0.88.

3. The alloy of claim 1, wherein the Mg and Si are present in an Mg/Si ratio of at least 0.69.

4. The alloy of claim 1 , wherein the Mg and Si are present in an Mg/Si ratio of 0.69 - 0 88

5. The alloy of claim 1, wherein the alloy includes excess Mg as defined by the following equation:

Excess Mg = Mg - (Si --- (Mn+Fe+Cr)/3)/1.16 (ail values in wt%).

6 The alloy of claim 5, wherein the alloy includes up to 0.40 wt.% excess Mg.

7. The alloy of claim 1 , wherein the alloy, after homogenization, extrusion, and artificial ageing, has a predominantly non-recrystal iized microstructure.

8. The alloy of claim 1, wherein the alloy, after homogenization, extrusion, and artificial ageing, has a yield strength of at least 350 MPa and a tensile elongation of at least 8%.

9. The alloy of claim 1, wherein the alloy, after homogenization, extrusion, and artificial ageing, has a yield strength of at least 370 MPa.

10. The alloy of claim 1 , wherein the alloy includes Mg in an amount of 0.60 - 0.80 wt.% and Si in an amount of 0.85 - 1.10 wt.%.

11. The alloy of claim 1, wherein the alloy includes Mg in an amount of 0.70 - 0.80 wt.% and Si in an amount of 0.85 - 0.95 wt.%.

12. The alloy of claim 1, wherein the Si and Mg in amounts are within a quadrilateral defined by the following coordinates on the Mg/Si plot, in weight percent:

I 1.15 Si, 0.70 Mg

II 0.95 Si, 0.55 Mg

II : 0.80 Si, 0.65 Mg

IV’: 0.95 Si, 0.80 Mg.

13. An extruded product formed at least partially of the aluminum alloy of claim 1.

14. An aluminum alloy comprising, in weight percent:

Mg 0.60 - 0.80

Si 0.85 - 1.10

Mn 0.40 - 0.80

Fe 0.25 max

Cr 0.05 - 0.18

Cu 0.30 - 0.90

Ti 0.05 max

Zr 0.03 max

Zn 0.03 max

B 0.01 max

with the remainder of the alloy being aluminum and unavoidable impurities in amounts of up to 0.05 each and 0.15 total.

15. The alloy of claim 14, wherein the Mg and Si are present in an Mg/Si ratio of no more than 0.88.

16. The alloy of claim 14, wherein the Mg and Si are present in an Mg/Si ratio of at least 0 69.

17. The alloy of claim 14, wherein the Mg and Si are present in an Mg/Si ratio of 0.69 - 0 88

18. The alloy of claim 14, wherein the alloy includes excess Mg as defined by the following equation:

Excess Mg = Mg - (Si - (Mn+Fe+Cr)/3)/1.16 (ail values in wt%).

19. The alloy of claim 18, wherein the alloy includes up to 0.40 wt.% excess Mg.

20. The alloy of claim 14, wherein the alloy, after homogenization, extrusion, and artificial ageing, has a predominantly non-recrystaliized microstructure.

21. The alloy of claim 14, wherein the alloy, after homogenization, extrusion, and artificial ageing, has a yield strength of at least 350 MPa and a tensile elongation of at least 8%.

22. The alloy of claim 14, wherein the alloy, after homogenization, extrusion, and artificial ageing, has a yield strength of at least 370 MPa.

23. The alloy of claim 14, wherein the alloy includes Mg in an amount of 0.70 - 0.80 wt.% and Si in an amount of 0.85 - 0.95 wt.%.

24. An extruded product formed at least partially of the aluminum alloy of claim 14.

25. A method comprising:

producing a billet of an aluminum alloy comprising:

I 1.15 Si, 0.70 Mg

II 0.95 Si, 0.55 Mg

III 0.75 Si, 0.65 Mg

IV 0.95 Si, 0.85 Mg

wherein the alloy further comprises, in weight percent:

Mn 0.40 - 0.80

Fe 0.25 max Cr 0.05 - 0.18

Cu 0.30 - 0.90

Ti 0.05 max

Zr 0.03 max

Zn 0.03 max

B 0.01 max

with the remainder of the alloy being aluminum and unavoidable impurities in amounts of up to 0.05 wt.% each and 0 15 wt.% total;

homogenizing the billet at a temperature of 540-580°C for 2-10 hours; and extruding the billet after homogenization to form an extruded product

26. A method comprising:

producing a billet of an aluminum alloy comprising:

Mg 0.60 - 0.80

Si 0.85 - 1.10

Mn 0.40 - 0.80

Fe 0.25 max

Cr 0.05 - 0.18

Cu 0.30 - 0.90

Ti 0.05 max

Zr 0.03 max

Zn 0.03 max

B 0.01 max

with the remainder of the alloy being aluminum and unavoidable impurities in amounts of up to 0.05 wt.% each and 0.15 wt.% total;

homogenizing the billet at a temperature of 540-580°C for 2-10 hours; and extruding the billet after homogenization to form an extruded product.