KR20250011123A - Aluminum alloy with improved strength and ductility - Google Patents

Abstract

The present disclosure relates to an aluminum alloy having improved strength and ductility. The aluminum alloy composition achieves a superior strength/ductility combination compared to conventional Al-Mg-Si alloys. The aluminum alloy may be particularly suitable for applications requiring a yield strength exceeding 240 MPa. The aluminum alloy comprises, in wt. %, 0.41 to 0.59 Si; ≤ 0.3 Fe; 0.08 to 0.30 Cu; 0.45 to 0.55 Mg; 0.08 to 0.20 Mn; and the remainder being aluminum and unavoidable impurities. In the aluminum alloy, Mn may be replaced by Cr, such that an equivalence ratio of Mn to Cr is Mn = 1.6Cr, wherein Mn + 1.6Cr + Cu ≥ 0.25.

Description

Aluminum alloy with improved strength and ductility

Cross-reference to related applications

This application claims the benefit of U.S. Provisional Application No. 63/364,890, filed May 18, 2022, the contents of which are incorporated herein by reference in their entirety.

The present disclosure relates to the field of aluminum alloys, such as Al-Mg-Si alloys, particularly aluminum alloys useful in the automotive industry.

Aluminum alloys are used in the automotive industry because they have desirable mechanical properties suitable for that industry. In automotive extrusion applications, it is desirable to increase strength in order to increase energy absorption and to reduce the wall thickness of the part, thereby reducing the weight of the car. Good ductility is also required to cope with plastic deformation during the forming operation of the part and to withstand severe plastic deformation without generating cracks that could limit energy absorption in a crash situation. In conventional Al-Mg-Si based extrusion alloys, the strength can be increased by increasing the concentration of the major elements Mg and Si, but generally, increasing the strength comes at the expense of ductility, as measured by flexural testing or fracture strain.

It is desirable to manufacture aluminum alloys that increase strength without compromising ductility, especially for use in the automotive industry.

In one aspect, an aluminum alloy is provided comprising, in wt %, 0.41 - 0.59 Si; ≤ 0.3 Fe; 0.08 - 0.30 Cu; 0.45 - 0.55 Mg; 0.08 - 0.20 Mn (or wherein Mn is replaced by Cr such that the equivalence ratio of Mn to Cr is Mn = 1.6Cr); and the remainder aluminum and unavoidable impurities, wherein Mn + 1.6Cr + Cu ≥ 0.25. In some embodiments, the aluminum alloy comprises up to 0.12 wt % Cr. In some embodiments, the unavoidable impurities comprise less than 0.1 wt % of the aluminum alloy, each unavoidable impurity being present up to 0.05 wt %. In some embodiments, the unavoidable impurities comprise ≤ 0.05 wt % Ni. In some embodiments, the unavoidable impurities comprise ≤ 0.05 wt % Zn. In some embodiments, the inevitable impurities comprise ≤ 0.05 wt % Ti. In some embodiments, the inevitable impurities comprise ≤ 0.05 wt % B. In some embodiments, the inevitable impurities comprise ≤ 0.05 wt % V. In some embodiments, the alloy comprises 0.43 - 0.55 Si. In some embodiments, the alloy comprises ≤ 0.25 Fe. In some embodiments, the alloy comprises 0.10 - 0.30 Cu. In some embodiments, the alloy comprises 0.47 - 0.53 Mg. In some embodiments, the alloy comprises 0.10 - 0.20 Mn. In some embodiments, the alloy comprises at least 0.10 Fe. In some embodiments, the alloy comprises up to 0.10 Cr. In some embodiments, the alloy comprises 0.48 - 0.52 Mg. In some embodiments, the alloy further comprises a grain refiner.

In one aspect, an aluminum alloy is provided comprising, in wt %, 0.41 - 0.59 Si; ≤ 0.3 Fe; 0.08 - 0.30 Cu; 0.45 - 0.55 Mg; up to 0.20 Mn; up to 0.12 Cr; and the remainder aluminum and unavoidable impurities. In some embodiments, the unavoidable impurities comprise less than 0.1 wt % of the aluminum alloy, each unavoidable impurity being present at up to 0.05 wt %. In some embodiments, the unavoidable impurities comprise ≤ 0.05 wt % Ni. In some embodiments, the unavoidable impurities comprise ≤ 0.05 wt % Zn. In some embodiments, the unavoidable impurities comprise ≤ 0.05 wt % Ti. In some embodiments, the unavoidable impurities comprise ≤ 0.05 wt % B. In some embodiments, the unavoidable impurities comprise ≤ 0.05 wt % V. In some embodiments, the alloy comprises 0.43 - 0.55 Si. In some embodiments, the alloy comprises ≤ 0.25 Fe. In some embodiments, the alloy comprises 0.10 - 0.30 Cu. In some embodiments, the alloy comprises 0.47 - 0.53 Mg. In some embodiments, the alloy comprises 0.08 - 0.20 Mn. In some embodiments, the alloy comprises at least 0.10 Fe. In some embodiments, the alloy comprises up to 0.10 Cr. In some embodiments, the alloy comprises 0.48 - 0.52 Mg. In some embodiments, the alloy further comprises a grain refiner. In some embodiments, the aluminum alloy comprises a combined Cu, Mn, and Cr concentration in wt. % Cu + Mn + 1.6Cr ≥ 0.25. In some embodiments, the aluminum alloy comprises Cu + Mn ≥ 0.25 or Cu + 1.6Cr ≥ 0.25. In some embodiments, the aluminum alloy comprises a combined Mn and Cr concentration of up to 1.6Cr in wt. %.

In one aspect, an aluminum product comprising an aluminum alloy of the present disclosure is provided. The aluminum product may have a recrystallized grain structure. The aluminum product may be an extruded billet. The aluminum product may be an automotive component.

Also provided is a process for manufacturing an aluminum product, comprising the steps of: casting an aluminum alloy described herein to manufacture a cast aluminum product; extruding the cast aluminum product to manufacture an extruded aluminum product; and cooling the extruded aluminum product.

In one embodiment, the aluminum alloy is cast by direct chill casting, continuous casting and/or semi-continuous casting. Preferably, the aluminum alloy is cast using a Properzi continuous casting, a twin roll caster, or a block caster. In another embodiment, the extruded aluminum product is cooled using cooling fans, water sprays, or water quenching. In one embodiment, the cast aluminum product is extruded by hollow extrusion. In a further embodiment, the process described herein further comprises a step of heat treating or homogenizing the cast aluminum product prior to extrusion.

Many additional features and combinations thereof relating to improvements of the present invention will become apparent to those skilled in the art upon reading this disclosure.

Figure 1 is a plot of ductility measured by longitudinal VDA bending angle versus yield strength after artificial aging treatment.
Figure 2 is a plot of the ductility measured by the transverse bending angle versus the yield strength.
Figure 3 is a plot of the ductility measured by actual breaking strain versus yield strength.
Figure 4 is a plot of the Mn and Cu contents of the tested alloys.

The present disclosure relates to aluminum alloys having improved strength and ductility. The aluminum alloy compositions of the present disclosure achieve a superior strength/ductility combination compared to conventional Al-Mg-Si alloys. In some embodiments, the aluminum alloys are particularly suitable for applications requiring yield strengths exceeding 240 MPa. The Al-Mg-Si alloys of the present disclosure surprisingly achieve the improved strength and ductility combination through controlled additions of 0.08 - 0.30 Cu and 0.08 - 0.20 Mn. The improved strength and ductility can be measured, for example, by comparison with conventional 6XXX automotive extruded aluminum alloys (e.g., AA6060 and AA6063). More specifically, the aluminum alloy of the present disclosure comprises, in some embodiments, in wt%, 0.41 to 0.59 Si, ≤ 0.3 Fe, 0.08 to 0.30 Cu, 0.45 to 0.55 Mg, optionally up to 0.12 Cr and 0.08 to 0.20 Mn, the remainder being aluminum and unavoidable impurities. The content of Mn, Cr (in a Mn:1.6Cr ratio) and Cu is at least 0.25 wt%. The alloy included in the present disclosure can be cast as an extrusion billet and extruded into products such as an extruded profile for automotive applications.

The Si content of the aluminum alloy of the present disclosure is, in wt%, 0.41 to 0.59, 0.42 to 0.59, 0.43 to 0.59, 0.44 to 0.59, 0.41 to 0.58, 0.41 to 0.57, 0.41 to 0.56, 0.41 to 0.55, 0.41 to 0.54, 0.41 to 0.53, 0.41 to 0.52, 0.41 to 0.51, 0.41 to 0.50, 0.41 to 0.49, 0.41 to 0.48, 0.41 to 0.47, 0.41 to 0.46, 0.41 to 0.45, 0.42 to 0.50, 0.43 to 0.50, 0.42 to 0.48, 0.43 to 0.47, or 0.43 to 0.45. Silicon improves the strength of the Al alloy by imparting precipitation hardening when combined with Mg and Cu, and also promotes the formation of an Al-Mn-Fe-Si dispersion which can prevent slip localisation.

The aluminum used to make the alloys described herein can be a primary aluminum alloy or a recycled material. Fe is a natural impurity in primary aluminum and can also be present at high levels in recycled materials, and the claims reflect the use of materials from both of these sources. The Fe content of the aluminum alloys of the present disclosure, in wt. %, based on the total weight of the aluminum alloy, is at most 0.3, at most 0.25, at most 0.22, at most 0.21, at most 0.20, from 0.10 to 0.30, from 0.10 to 0.25, from 0.10 to 0.22, from 0.10 to 0.20, from 0.12 to 0.25, from 0.13 to 0.24, from 0.14 to 0.23, or from 0.15 to 0.22. The amount of Fe is limited to a maximum of 0.3, preferably a maximum of 0.25, more preferably a maximum of 0.22, in order to avoid any negative influence on the mechanical properties of the aluminum alloy. Fe has a low solubility in aluminum and usually forms intermetallic compounds or constituent particles during casting and homogenization, which can adversely affect the surface finish of the shaped part and, when present in high concentrations, can adversely affect the ductility. For this reason, the upper limit of the Fe content is preferably, as described herein, for example, a maximum of 0.3, a maximum of 0.25 or a maximum of 0.2.

The Cu content of the aluminum alloy of the present disclosure is, in wt%, based on the total weight of the aluminum alloy, 0.08 to 0.30, 0.09 to 0.30, 0.10 to 0.30, 0.11 to 0.30, 0.12 to 0.30, 0.13 to 0.30, 0.14 to 0.30, 0.15 to 0.30, 0.16 to 0.30, 0.17 to 0.30, 0.18 to 0.30, 0.19 to 0.30, 0.08 to 0.29, 0.08 to 0.28, 0.08 to 0.27, 0.08 to 0.26, 0.08 to 0.25, 0.08 to 0.24, 0.08 0.23, 0.08 to 0.22, 0.08 to 0.21, 0.08 to 0.20, 0.10 to 0.29, 0.10 to 0.28, 0.10 to 0.27, 0.10 to 0.26, 0.10 to 0.25, 0.10 to 0.24, 0.10 to 0.23, 0.10 to 0.22, 0.10 to 0.21, 0.10 to 0.20, 0.11 to 0.19, 0.12 to 0.18 or 0.13 to 0.17. In addition to the usual MgSi precipitates, Cu promotes the formation of Al-Mg-Si-Cu aging precipitates such as Q" or Q', which can improve the slip dispersion during plastic deformation.

The Mg content of the aluminum alloy of the present disclosure is, in wt.%, 0.45 to 0.55, 0.45 to 0.54, 0.45 to 0.53, 0.45 to 0.52, 0.45 to 0.51, 0.45 to 0.50, 0.46 to 0.55, 0.47 to 0.55, 0.48 to 0.55, 0.49 to 0.55, 0.50 to 0.55, 0.46 to 54, 0.47 to 0.54, 0.48 to 0.54, 0.47 to 0.53, or 0.48 to 0.52, based on the total weight of the aluminum alloy. Magnesium contributes to solid solution strengthening. The main role of magnesium is to combine with Si and Cu to cause precipitation hardening.

The Mn content of the aluminum alloy of the present disclosure is, in wt.%, at most 0.20, at most 0.19, at most 0.18, at most 0.17, at most 0.16, at most 0.15, 0.08 to 0.20, 0.08 to 0.19, 0.08 to 0.18, 0.08 to 0.17, 0.08 to 0.16, 0.08 to 0.15, 0.08 to 0.14, 0.09 to 0.20, 0.09 to 0.19, 0.09 to 0.18, 0.09 to 0.17, 0.09 to 0.16, 0.09 to 0.15, 0.09 to 0.14, 0.10 to 0.20, 0.10 to 0.19, 0.10 to 0.18, 0.10 to 0.17, 0.10 to 0.16, 0.10 to 0.15, 0.10 to 0.14, 0.11 to 0.16 or 0.12 to 0.15. Mn can contribute to the strength of Al alloys by dispersion strengthening and solid solution hardening. Mn promotes the formation of Al-Mn-Fe-Si submicron dispersion particles during homogenization. These dispersions can delay the concentration of internal stresses and the occurrence of fracture by dispersing slip during plastic deformation. Mn also promotes extrudability by facilitating the transformation of β Al-(Fe,Mn)Si composition to α. However, excessive amounts of dispersed particles can increase the flow stress of the alloy at extrusion temperatures and adversely affect the extrusion rate, along with inhibition of recrystallization to form coarse recrystallized or non-recrystallized grain structures.

In some embodiments, the combined Cu and Mn content of the aluminum alloy of the present disclosure is at least 0.25, at least 0.26, at least 0.27, at least 0.28, or at least 0.29 wt. %. In some embodiments, the combined Cu and Mn content is at least 0.05 Mn, at least 0.06 Mn, at least 0.07 Mn, or at least 0.08 Mn wt. %. In a further embodiment, the combined Cu and Mn content is at least 0.08 Mn. Indeed, it has surprisingly been found that combining Cu and Mn within their respective specified minimum ranges improves the strength of the aluminum alloy while advantageously maintaining or improving ductility. This is demonstrated in the Examples section below.

In some embodiments, Cr may act to substitute for or complement Mn. In fact, the dispersion particles formed by the addition of Cr and Mn have similar crystal cubic structures with similar lattice constants and are mutually soluble to some extent such that the two elements are interchangeable. Therefore, the Cr content of the aluminum alloy of the present disclosure can be, in wt.%, at most 0.12, at most 0.11, at most 0.10, at most 0.09, at most 0.08, at most 0.07, at most 0.06, 0.03 to 0.12, 0.03 to 0.11, 0.03 to 0.10, 0.03 to 0.09, 0.05 to 0.12, 0.05 to 0.11, 0.05 to 0.10, 0.05 to 0.09, 0.06 to 0.12, 0.06 to 0.11, 0.06 to 0.10, 0.06 to 0.09 or 0.07 to 0.08, based on the total weight of the aluminum alloy. In some embodiments, the minimum Cr content is at least 0.03 wt. %, at least 0.04 wt. %, at least 0.05 wt. %, or more than 0.05 wt. %. In other embodiments, Cr may not be included in the alloy, and thus the aluminum alloy may include less than 0.05 wt. %, less than 0.03 wt. %, or less than 0.01 wt. % Cr. In some embodiments, Cr may be used instead of Mn, and vice versa. In one embodiment, Mn is replaced by Cr, such that the equivalence ratio of Mn to Cr is Mn = 1.6Cr. In another embodiment, the alloy does not include Cr when Mn is at least 0.1 wt. %.

Since Mn and Cr are exchangeable, only a portion of Mn can be replaced by Cr (and vice versa). Therefore, the overall content of Mn, Cr, and Cu of the alloy of the present invention can be set as follows: Mn + 1.6Cr + Cu ≥ 0.25 wt. %. In some embodiments, the concentration of Mn + 1.6Cr + Cu can be at least 0.26 wt. %, at least 0.27 wt. %, at least 0.28 wt. %, or at least 0.29 wt. %. In such embodiments, the total content of Mn and Cr is defined as follows: Mn + 1.6Cr ≤ 0.20.

Since Mn and Cr are exchangeable, in some embodiments, the aluminum alloy of the present disclosure can have a combined content of Cr and Cu that can be defined as: Cu + 1.6Cr ≥ 0.25. In such embodiments, Cr can completely substitute for Mn. In some embodiments, Cu + 1.6Cr can be at least 0.26, at least 0.27, at least 0.28, or at least 0.29. Accordingly, in some embodiments, the aluminum alloy can be defined as having Cu + 1.6Cr ≥ 0.25 with Mn being less than 0.05 wt. %, or having Mn + Cu ≥ 0.25 with Cr being less than 0.05 wt. %.

The weight percent concentration of the aluminum alloy is provided such that the remainder is aluminum and unavoidable impurities. In some embodiments, each of the unavoidable impurities is present in an amount of at most 0.05 (in some embodiments, 0.03) and the total unavoidable impurities comprises less than 0.10. In some embodiments, the term "unavoidable impurities" should be understood to mean that there are no intentional additions.

In some embodiments, the unavoidable impurity comprises Ni in a concentration of 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less. Ni has very low solubility in aluminum and forms undesirable constituent particles. Ni may be present as an impurity from the anode in the reduction process.

In some embodiments, the unavoidable impurity includes Zn in a concentration of 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less. The presence of Zn can adversely affect the corrosion performance of the alloy.

In some embodiments, the unavoidable impurities include Ti in a concentration of 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less.

In some embodiments, the unavoidable impurities include B in a concentration of 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less.

In some embodiments, the unavoidable impurities include V in concentrations of 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less. V is detrimental to the extrudability of aluminum alloys and is generally only an impurity resulting from the reduction process.

In some embodiments, the unavoidable impurities include Zr in a concentration of 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, 0.01 or less.

In some embodiments, the aluminum alloy of the present disclosure comprises, consists essentially of, or consists of any combination of Si, Fe, Cu, Mg, Mn, Cu+Mn, Cr, and incidental impurities in the concentration ranges described above.

In some embodiments, the aluminum alloy optionally further comprises a grain refiner, such as titanium, titanium boride, or titanium carbide, for solidifying the aluminum alloy. In one embodiment, the grain refiner is in the form of Ti, TiB or TiC. When TiB is used as the grain refiner, the content of B in the alloy can be at most 0.05 wt. %. When TiC is used as the grain refiner, the content of C in the alloy can be at most 0.01 wt. %. Ti dissolved in the molten aluminum can promote the formation of an interfacial TiAl ₃ layer between the TiB ₂ /melt interface, which subsequently promotes nucleation of Al grains.

The present disclosure also provides a process for manufacturing a high strength aluminum product using the aluminum alloy of the present disclosure. In a first step, the process comprises casting the aluminum alloy of the present disclosure to obtain a cast aluminum product. The casting step may comprise, for example, direct chill casting, continuous casting, and/or semi-continuous casting. Properch continuous casting may be used, which may be a wheel and belt casting process or a track and belt casting process. The track and belt process replaces the casting wheel with a plurality of copper blocks. Other options may be used, including a twin roll caster. A twin roll caster has two rolls that rotate and continuously advance the mold. The rolls may be cooled to aid in solidification of the molten aluminum alloy. A further option includes a block caster having a block adapted to function as a belt. The block may be cooled to aid in solidification of the molten aluminum alloy.

In the second step, the cast aluminum product is extruded to become an extruded aluminum product. During extrusion, the aluminum alloy is heated to a temperature at which the alloy is malleable. A press container may be used in front of the die orifice. A hydraulic ram may be used to apply pressure to fill the container with the aluminum alloy, and the die may be used to form the desired shape. After hot deformation (i.e., extrusion or propeller hot rolling), the aluminum alloy may be actively cooled using cooling fans and/or water spray or complete water quenching. In a preferred embodiment, a quenching rate of 20° C./sec at 500 to 300° C. is used. Most automotive extrusions are hollow to improve rigidity and crush performance. Therefore, in some embodiments, the extrusion is a hollow extrusion, such as a hollow automotive extrusion. Water quenching at the press exit, typically spray quenching, is generally preferred because it is more malleable than, for example, air quenching. The improvement in water quenching over air quenching may be related to the change in microstructure at grain boundaries.

A fully recrystallized grain structure has advantages over a non-recrystallized grain structure (typically having a coarse recrystallized grain surface layer) in automotive applications. These include reduced sensitivity of strength to press quench rate, absence of surface orange peel which can be an initiation site for fatigue and corrosion, and improved ductility of localized extrusion weld lines. Additionally, higher levels of dispersion forming elements such as Mn and Cr required to produce a non-recrystallized grain structure can typically result in lower quench sensitivity of extrudability and strength. In some embodiments, the present aluminum alloys achieve a fully recrystallized grain structure to benefit from these advantages, and this fully recrystallized structure is a characteristic of the product.

In one embodiment, the process further comprises heat treating or homogenizing the cast aluminum product after casting and prior to extrusion. The heat treating conditions can be at a temperature of from about 450 to about 600°C, from about 500 to about 600°C, from about 550 to about 590°C or from about 560 to about 580°C for a period of at least about 1 hour, at least about 2 hours, at least about 3 hours, at least about 4 hours or at least about 5 hours. In some embodiments, the aluminum product is an extruded billet.

The strength and ductility of aluminum alloys can be determined by a variety of suitable methods. However, the elongation to failure during a tensile test is not a useful parameter for predicting crash performance. On the other hand, the ductility of extruded materials can be evaluated by bending tests in the direction of the extrusion or transversely to the direction of the extrusion according to the German Association of the Automotive Industry (VDA 238-100). Such bending tests can simulate the strains applied during bending in axial or transverse crush or during mechanical joining such as self-penetrating riveting. The actual strain to failure (Ln (initial cross-sectional area/ultimate fracture area)) measured in a tensile test is a useful measure of ductility for such applications.

In some embodiments, the ultimate tensile strength (UTS) of the aluminum product of the present disclosure is at least 250, at least 255, at least 259, or at least 265 MPa. In some embodiments, the yield strength of the aluminum product of the present disclosure is at least 230, at least 235, at least 240, greater than 240, at least 245, at least 250, or at least 255 MPa. In some embodiments, the longitudinal VDA bend angle of the aluminum product of the present disclosure is at least 105, at least 109, at least 115, or at least 119° for a thickness of 2.5 mm. In some embodiments, the transverse VDA bend angle of the aluminum product of the present disclosure is at least 58, 59, 60, 61, 62, 63, 64, or 65°. In some embodiments, the actual fracture strain of the aluminum product of the present disclosure is at least 0.65, at least 0.66, at least 0.67, at least 0.68, at least 0.69, at least 0.70, at least 0.71, at least 0.72, at least 0.73, at least 0.73, at least 0.74, at least 0.75 or at least 0.75 when the aluminum product has a thickness of 2.5 mm.

Example

The alloy composition shown in Table 1 was direct chill cast (DC cast) into 101 mm diameter billets. 5%Ti-1%B grain refiner was added prior to casting. The billets were homogenized at 580°C for 2 h and then forced air cooled at 450°C/hr between 500 and 200°C. They were extruded into 50x20x2.5 mm hollow box profiles using a billet preheat temperature of 500°C and an extrusion exit speed of 13 m/min. The die was constructed such that the extrusion weld was positioned at a 20 mm face of the profile so that characterization was performed on a 50 mm wide face away from the extrusion weld. After exiting the die, the profiles were water-spray quenched at 150°C/sec between 500 and 300°C. The quenching speed was measured using a clip-on contact thermocouple attached to a high-frequency logger with a WiFi transmitter. The cooled profiles were drawn to impart a permanent strain of 0.5 % and aged at 177°C for 8 h after a room temperature delay of 24 h. Tensile tests were performed in the longitudinal direction according to ASTM E8 and the fracture area projected in the tensile direction was measured using image analysis techniques, from which the actual fracture strain could be calculated using the equation Ln (initial cross-sectional area/final fracture area). A higher value of the fracture strain indicates better bendability. VDA bend tests were performed in the longitudinal (bending axis perpendicular to the extrusion direction) and transverse (bending axis parallel to the extrusion direction) orientations using a punch radius of 0.4 mm, a roller spacing of twice the material thickness, i.e., 5 mm and a load drop of 60 N. The complementary bend angle was measured after the load was removed and an increasing bend angle indicates better ductility or bendability.

Table 1: Alloy composition I.D. Alloy type weight% Si Fe Cu Mn Mg Cr Ti V A .02Mn 0.44 0.17 <0.001 0.02 0.50 <0.001 0.015 0.012 B .08Mn 0.43 0.17 <0.001 0.08 0.50 <0.001 0.01 0.014 C .08Mn- .08Cu 0.44 0.17 0.08 0.08 0.52 <0.001 0.005 0.014 D .08Mn- .26Cu 0.45 0.20 0.26 0.08 0.50 <0.001 0.015 0.014 E .13Mn- .15Cu 0.44 0.19 0.15 0.13 0.50 0.001 0.013 0.012 F .13Mn- .19Cu 0.43 0.19 0.19 0.13 0.50 0.001 0.019 0.012 G .14Mn- .25Cu 0.45 0.20 0.26 0.14 0.51 <0.001 0.013 0.014 H .14Mn 0.44 0.18 <0.001 0.14 0.50 <0.001 0.01 0.014 I .18Mn- .0.08Cu 0.44 0.17 0.08 0.18 0.52 <0.001 0.017 0.015 J .20Mn 0.44 0.18 <0.001 0.21 0.50 <0.001 0.01 0.014 K HiSi- .08Mn 0.62 0.17 0.002 0.08 0.48 0.001 0.01 0.005 L HiSi- .20Mn 0.65 0.17 0.002 0.20 0.48 0.001 - -

Alloy A represents a typical commercial AA6063 alloy for automotive and other applications, and Alloy K represents a typical commercial high-strength AA6063 with increased silicon content. The addition of 0.02 - 0.08 wt.% Mn in these types of alloys is intended to promote the transformation of β Al-(Fe,Mn)Si phase to α phase, thereby improving extrudability. Compositions B-J and L represent increments of independent and combined additions of Mn and Cu.

Table 2 shows the results of mechanical properties of each composition, where VDA-L is the longitudinal bending angle test, VDA-T is the transverse bending angle test, El is the elongation, Ef is the actual breaking strain, YS is the yield strength, and UTS is the ultimate tensile strength.

Table 2: Alloy test results I.D. Alloy type YS UTS El VDA-L VDA-T Ef MPa MPa % angle angle A .02Mn 224.2 242.7 10.1 121 73 0.86 B .08Mn 220.6 242.5 12.0 127 80 0.97 C .08Mn- .08Cu 244.7 266.7 12.0 114 57 0.77 D .08Mn- .26Cu 261.6 288.7 13.2 109 61 0.66 E .13Mn- .15Cu 248.0 272.1 12.8 120 67 0.79 F .13Mn- .19Cu 251 278.1 12.7 122 65 0.76 G .14Mn- .25Cu 259.4 283.5 12.6 119 71 0.84 H .14Mn 215.4 238.3 11.9 129 101 0.95 I .18Mn- .0.08Cu 236.3 259.1 12.1 123 81 1.00 J .20Mn 212.4 235.0 11.2 129 101 0.97 K HiSi- .08Mn 260.4 276.7 11.3 106 35 0.55 L HiSi- .20Mn 259.3 275.2 10.9 108 38 0.58

The microstructures of the extruded materials were evaluated metallographically. All microstructures exhibited a fully recrystallized grain structure, which is desirable for this type of product to improve bulk and local ductility at the extrusion weld line. The aluminum alloys showed a general trend of decreasing ductility (measured by VDA bend angle or strain at break) with increasing yield strength, which is primarily a result of the increased stress levels applied to the microstructure, which promotes early initiation of fracture. Figure 1 is a plot of longitudinal VDA bend angle versus yield strength after artificial aging. Each point is labeled with an alloy I.D. from Table 1. Reference alloys A and K are located within the band, along with alloys J, H, B, L with increased Mn additions, and alloy C with a composite addition of 0.08 wt.% Mn and 0.08 wt.% Cu. The addition of Mn to alloy A slightly increases the bend angle, but also decreases the strength, which is not desirable. Addition of 0.20 wt% Mn to the reference alloy K slightly decreases the yield strength but slightly increases the bend angle. However, alloys D, E, F, G and I of the present invention with composite additions of Mn and Cu significantly improve the ductility by providing strengths that are improved over the reference alloy A at the same ductility or equivalently high strength to the reference alloy K. FIGS. 2 and 3 plot the transverse VDA bend angle and the true fracture strain, which are other measures of ductility, against the yield strength. The trends are very similar to those in FIG. 1 , and alloys D, E, F G and I have an excellent combination of strength and ductility. As can be seen by comparing FIGS. 1 and 2 , the bend angle measured transversely to the extrusion direction is typically smaller than the bend angle measured longitudinally.

Figure 4 is a plot of Mn content versus Cu content of the experimental alloy, separating the compositions in the same direction as depicted in Figures 1 to 3. The compositions exhibiting enhanced strength and ductility (black dots) can be distinguished from the reference strength and ductility compositions by the line corresponding to Mn + Cu > 0.20 wt.%, preferably Mn + Cu ≥ 0.25 wt.%, as depicted in Figure 4, where the effective Mn is calculated using Mn + 1.6Cr.

All test materials were water jet quenched after extrusion, which was a necessary step to achieve high ductility. In fact, ductility is significantly improved with increasing quenching rate associated with this type of cooling.

The alloy composition in Table 3 was DC cast as a 101 mm diameter billet. 5%Ti-1%B grain refiner was added prior to casting. The billet was homogenized at 580°C for 2 h and then forced air cooled at 450°C/hr between 500 and 200°C. It was extruded into a 50x20x2.5 mm hollow box profile using a billet preheat temperature of 500°C and an extrusion exit speed of 13 m/min. The profile was spray quenched at the die exit at a rate of 150°C/sec. The cooled profile was drawn to impart a permanent plastic elongation of 0.5% and aged at 177°C for 8 h after a room temperature delay of 24 h. Mechanical tests including tensile and VDA bending tests were performed in a similar manner to the previous examples.

Table 3: Alloy composition for Mn substitution test by Cr

Alloy M is a repeat casting of alloy G, which in the examples reported in the specification showed improved ductility as measured by VDA for a given yield strength. Alloys N and O were prepared to evaluate the effect of partial and complete substitution of Mn by Cr while keeping the Mg, Si and Cu contents fixed. As provided herein, these two elements (Mn and Cr) are exchangeable in the submicron dispersion particles formed during homogenization.

Table 4 shows the results of mechanical properties for the three compositions listed in Table 3. The tensile properties and ductility values measured by VDA bending angle are almost identical, indicating that partial and complete substitution of Mn by Cr is effective in maintaining excellent strength and ductility.

Table 4: Mechanical properties of alloy compositions in Table 3

The yield strength and VDA bend angle of the tested compositions are shown in Fig. 1 (longitudinal VDA) and Fig. 2 (transverse VDA). In Fig. 1, alloys M, N and O provide similar yield strength values as the original alloy G, but slightly lower longitudinal bend angles. This can be explained by the slight difference in test conditions between the extrusion tests. However, all three compositions provided superior performance over the band of the reference alloy, indicating that Cr can be substituted with Mn as exemplified herein. A similar trend was observed for the transverse bend angle in Fig. 2. The results for all three compositions M, N and O fall within the improved strength/ductility band over the reference strength and ductility.

As demonstrated, Cr can be used to partially or completely replace Mn as a dispersion forming element.

While the present disclosure has been described with respect to specific embodiments thereof, it will be understood that it may be modified further, and that the present application is intended to cover any changes, uses, or adaptations which come within the practice of the art and which depart from the present disclosure in its essential features as set forth above and which are within the scope of the appended claims.

Claims (27)

As an aluminum alloy, in weight %:
0.41 - 0.59 Si;
≤ 0.3 Fe;
0.08 - 0.30 Cu;
0.45 - 0.55 Mg;
0.08 to 0.20 Mn - or Mn is replaced by Cr in an equivalent ratio of Mn to Cr, Mn = 1.6Cr, where Mn + 1.6Cr + Cu ≥ 0.25 -; and
Residual aluminum and unavoidable impurities
An aluminum alloy comprising: In the first paragraph,
The above alloy is an aluminum alloy containing 0.08 to 0.20 Mn. In the first paragraph,
An aluminum alloy in which Mn is replaced by Cr in the equivalent ratio of Mn to Cr in the alloy, Mn = 1.6Cr. In any one of claims 1 to 3,
An aluminum alloy, wherein the above inevitable impurities comprise less than 0.1 wt% of the aluminum alloy, and each inevitable impurity is present at a maximum of 0.05 wt%. In any one of claims 1 to 4,
An aluminum alloy containing the above inevitable impurities of ≤ 0.05 wt% Ni. In any one of claims 1 to 5,
An aluminum alloy containing the above inevitable impurities of ≤ 0.05 wt% Zn. In any one of claims 1 to 6,
An aluminum alloy containing the above inevitable impurities of ≤ 0.05 wt% Ti. In any one of claims 1 to 7,
An aluminum alloy containing the above inevitable impurities of ≤ 0.05 wt% B. In any one of claims 1 to 8,
An aluminum alloy containing the above inevitable impurities of ≤ 0.05 wt% V. In any one of claims 1 to 9,
An aluminum alloy containing 0.43 - 0.55 wt% Si. In any one of claims 1 to 10,
An aluminum alloy containing ≤ 0.25 wt% Fe. In any one of claims 1 to 11,
An aluminum alloy containing 0.10 - 0.30 wt% Cu. In any one of claims 1 to 12,
An aluminum alloy containing 0.47 - 0.53 wt% Mg. In any one of claims 1 to 13,
An aluminum alloy containing 0.10 - 0.20 wt% Mn. In any one of claims 1 to 14,
An aluminum alloy containing at least 0.10 wt% Fe. In any one of claims 1 to 15,
An aluminium alloy containing up to 0.10 wt% Cr. In any one of claims 1 to 16,
An aluminum alloy further comprising a grain refiner. An aluminum product comprising an aluminum alloy according to any one of claims 1 to 17. In Article 18,
An aluminum product having a recrystallized grain structure. In Article 18 or 19,
Extruded billet, aluminum product. In any one of Articles 18 to 20,
Aluminum products, which are automotive parts. A method for manufacturing an aluminum product,
a) a step of manufacturing a cast aluminum product by casting an aluminum alloy according to any one of claims 1 to 17;
b) a step of manufacturing an extruded aluminum product by extruding the cast aluminum product; and
c) A step of cooling the extruded aluminum product.
A method comprising: In Article 22,
A method wherein the above aluminum alloy is cast by direct chill casting, continuous casting and/or semi-continuous casting. In Article 22 or 23,
A method wherein the above aluminum alloy is cast using a Properzi continuous casting, a twin roll caster, or a block caster. In any one of Articles 22 to 24,
A method wherein the above extruded aluminum product is cooled using a cooling fan, water spray or water quenching. In any one of Articles 22 to 25,
A method in which the above cast aluminum product is extruded by hollow extrusion. In any one of Articles 22 to 26,
A method further comprising the step of heat treating or homogenizing the cast aluminum product prior to extrusion.