Aluminum sheet materials as well as production processes and alloy compositions for them with reduced energy consumption and CO2 emissions

Abstract

A process for producing aluminum sheet material comprises melting secondary aluminum and adding primary aluminum and other alloying elements to the melt to achieve an alloy composition of 2.5 wt.% to 6.3 wt.% Mg, 0.6 wt.% to 2.5 wt.% Si, 0.2 wt.% to 0.4 wt.% Fe, 0.05 wt.% to 0.2 wt.% Cr, up to 0.6 wt.% Mn, up to 0.1 wt.% Cu, and up to 0.1 wt.% Zn, the remainder consisting of Al and unavoidable impurities, wherein the Si and Mg contents satisfy the relationship (Si wt.% > 0.5 * Mg wt.% - 0.65 wt.%). The alloy is then processed into aluminum sheet by continuous casting. Aluminum sheet material produced by this process and an aluminum alloy suitable for this process are also disclosed.

Description

INTRODUCTION

[0001] The information provided in this section is intended to provide a general context for the disclosure. Work by the inventors identified herein, to the extent described in this section, as well as aspects of the description that may not be prior art at the time of filing, are neither expressly nor impliedly admitted as prior art over the present disclosure.

[0002] This disclosure relates to aluminum sheet materials and, in particular, to manufacturing processes and alloy compositions for reduced energy consumption and CO 2 -Emissions compared to conventional production of aluminum sheet materials.

[0003] Aluminum sheets used in the manufacture of automobiles and other products are typically made from primary aluminum, i.e., aluminum extracted directly from mined ore. This is because conventional manufacturing processes are not well suited to the use of secondary aluminum, such as aluminum scrap and recycled aluminum. However, producing aluminum sheets and manufacturing parts from them is very energy-intensive and can lead to the release of greenhouse gases, especially CO 2 , lead. SUMMARY

[0004] Embodiments of this disclosure provide methods for manufacturing aluminum sheet stock and large parts for commercial and consumer goods using substantial amounts of secondary aluminum with reduced energy consumption and CO 2 -Emissions compared to the production of such sheet material and parts from primary aluminum.

[0005] Embodiments of this disclosure further provide aluminum sheet material made with significant amounts of secondary aluminum, thereby reducing energy consumption and CO 2 emissions, yet is still suitable for producing large parts for commercial and consumer goods, such as automotive parts.

[0006] Embodiments of this disclosure further provide an aluminum alloy composition particularly suitable for use in manufacturing processes involving aluminum from secondary sources.

[0007] According to a first embodiment of this disclosure, a method is provided for producing an aluminum sheet material useful in producing large parts or commercial and consumer goods, such as automotive panels. Generally, the method comprises the following steps: melting secondary aluminum; adding primary aluminum and other alloying elements to the melt to obtain a composition consisting essentially of 2.5 to 6.3 wt% Mg, 0.6 to 2.5 wt% Si, 0.2 to 0.4 wt% Fe, 0.05 to 0.2 wt% Cr, up to 0.6 wt% Mn, up to 0.2 wt% Cu, up to 0.2 wt% Zn, with the balance being Al and unavoidable impurities, wherein the Si and Mg contents satisfy the relationship (Si wt% > 0.5 * Mg wt% - 0.65 wt%); and continuously casting the aluminum alloy into aluminum sheet. The alloy can be continuously cast using either a twin-roll continuous caster or a two-belt continuous caster.

[0008] According to a second embodiment of this disclosure, a continuously cast aluminum sheet material is provided. The aluminum sheet has a composition consisting essentially of 2.5 wt% to 6.3 wt% Mg, 0.6 wt% to 2.5 wt% Si, 0.2 wt% to 0.4 wt% Fe, 0.05 wt% to 0.2 wt% Cr, up to 0.6 wt% Mn, up to 0.2 wt% Cu, up to 0.2 wt% Zn, the balance Al, and unavoidable impurities, wherein the Si and Mg contents satisfy the relationship (Si wt% > 0.5 * Mg wt% - 0.65 wt%). The sheet may be cast using either a twin-roll continuous caster or a twin-belt continuous caster.

[0009] According to a third embodiment of this disclosure, an aluminum alloy suitable for continuous casting is provided. The aluminum alloy may comprise from 2.5 wt% to 6.3 wt% Mg, from 0.6 wt% to 2.5 wt% Si, from 0.2 wt% to 0.4 wt% Fe, from 0.05 wt% to 0.2 wt% Cr, up to 0.6 wt% Mn, up to 0.2 wt% Cu, up to 0.2 wt% Zn, the remainder being Al and unavoidable impurities, wherein the Si and Mg contents satisfy the relationship (Si wt% > 0.5 * Mg wt% - 0.65 wt%). The alloy is suitable for continuous casting using a twin-roll continuous caster or a twin-belt continuous caster.

[0010] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are provided for purposes of illustration only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, in which: Fig. 1 is a flowchart of a method according to a first exemplary embodiment of this disclosure; Fig. Figure 2A is a micrograph of an alloy according to the third embodiment of this disclosure, prepared according to the method of the first embodiment of this disclosure and comprising 0.17 wt.% Mn, showing a portion of the Al matrix. Eutectic Mg 2 Si particles and Al-(Cr, Fe, Mn)-Si particles; Fig. Figure 2B is a micrograph of an alloy according to the third embodiment of this disclosure, prepared according to the method of the first embodiment of this disclosure and comprising 0.37 wt.% Mn, showing a portion of the Al matrix. Eutectic Mg 2Si particles and Al-(Cr, Fe, Mn)-Si particles; Fig. 2C is a micrograph of an alloy according to the third embodiment of this disclosure, prepared according to the method of the first embodiment of this disclosure, comprising 0.62 wt% Mn, and showing primary Al-(Cr, Fe, Mn)-Si particles; Fig. 3 is a micrograph of an alloy according to the third embodiment of this disclosure, prepared according to the method of the first embodiment of this disclosure and comprising 0.62 wt% Mn, and showing an Al-(Cr, Fe, Mn)-Si particle; Fig. 4 is a diagram showing the relationship between the Mg and Si content and the solidification range, with the leading lines between the scale and the ranges on the diagram indicating specific solidification ranges; Fig.Figure 5A is a micrograph of the alloy in which bright areas indicate the presence of Mg in the alloy and the scale bar indicates 25 µm; Fig. Figure 5B is a micrograph of the alloy in which bright areas indicate the presence of Si in the alloy and the scale bar indicates 25 µm; Fig. Figure 5C is a micrograph of the alloy in which bright areas indicate the presence of Mn in the alloy and the scale bar indicates 25 µm; Fig. Figure 5D is a micrograph of the alloy where bright areas indicate the presence of Cr in the alloy and the scale bar indicates 25 µm; Fig. Figure 5E is a micrograph of the alloy where bright areas indicate the presence of Fe in the alloy and the scale bar indicates 25 µm.

[0012] Reference numerals may be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0013] A first embodiment of this disclosure provides methods for manufacturing aluminum sheet material and large parts for commercial and consumer goods using substantial amounts of secondary aluminum with reduced energy consumption and CO 2 emissions compared to producing such sheet material and parts from primary aluminum. Although even a minimal use of secondary aluminum reduces energy consumption and CO 2 -can reduce emissions In some embodiments of the process at least 30% secondary aluminum from scrap and recycling streams may be used and in others at least 60% secondary aluminum, and it is possible that the embodiments may comprise up to 100% secondary aluminum.

[0014] As in Fig. 1, according to this first embodiment 100, secondary aluminum is melted at 102. This secondary aluminum may come from one or more streams combined to achieve a composition that meets or approaches a target range. For example, as shown in Table 1, a stock of 5XXX aluminum scrap with the specified composition, a stock of 6063 aluminum scrap with the specified composition, and recyclable beverage cans may be combined in a ratio that results in a composition in or near a target composition range. Table 1 is exemplary only; more and / or different sources may be used, and the materials from these sources may be combined in different proportions. Table 1 Si (wt%) Fe (wt%) Cu (wt%) Mn (wt%) Mg (wt%) Zn (wt%) Cr (wt%) 5XXX scrap 0,12 + / -0,07 0,27 + / -0,08 0,02 0,02 0,20 + / -0,24 2,9 + / -1,2 0,01 + / -0,01 0,12 + / -0,08 6063 scrap 0,47 + / -0,11 0,19 + / -0,09 0,02 + / -0,02 - 0,53 + / -0,13 - - beverage can 03 0,5 0,2 1,1 1,3 0,05 - 50% 5XXX scrap + 30% 6063 scrap + 20% beverage cans 0,26 + / -0,07 0,29 + / -0,07 < 0,1 >0,2 1,9 + / -0,6 <0,1 0,06 + / -0,04

[0015] The composition of the melt is determined, and at 104 the composition is adjusted to be within the target range by adding primary aluminum to dilute components that are over-represented compared to the target composition, and alloying elements and master alloys may be added to increase the content of components that are under-represented compared to the target composition. The identity of the scrap and recycling streams and their relative proportions may be chosen so that at least 30% of the aluminum in the alloy comes from secondary sources, so that the primary aluminum accounts for less than 70% of the aluminum content, so that the resulting energy savings and reduced CO 2 justify the effort and cost. In some embodiments, the use of primary aluminum can be reduced to less than 40% of the total aluminum content.

[0016] The molten scrap and recycling material is adjusted by adding primary aluminum and other alloying components to achieve a composition consisting essentially of 2.5 wt% to 6.3 wt% Mg, 0.6 wt% to 2.5 wt% Si, 0.2 wt% to 0.4 wt% Fe, 0.05 wt% to 0.2 wt% Cr, up to 0.6 wt% Mn, up to 0.2 wt% Cu, up to 0.2 wt% Zn, with the remainder being Al and unavoidable impurities, with the silicon and magnesium contents satisfying the relationship (Si wt% > 0.5 * Mg wt% - 0.65 wt%). As in Fig.As shown in Figure 4, this composition exhibits a desirable solidification range (the difference between the liquidus temperature and the solidus temperature) for continuous casting processes that are more tolerant of compositional variations caused by using scrap and recycled material. In some embodiments, the solidification range is less than about 100°C, and in other embodiments, less than about 85°C.

[0017] The inventors have also found that, at least in some cases, it may be advantageous to control the Mn content, which can contribute to the formation of undesirable sludge particles. In cases where these particles could interfere with subsequent forming processes using the alloy sheets and cause unexpected cracks, it may be desirable to keep the Mn content below about 0.6 wt.%, as described in Fig.3, although this may not be important for some applications.

[0018] Once the alloy composition is adjusted to the desired composition, it can be continuously cast at 106 using either a twin-roll caster or a dual-belt caster. A dual-belt caster can achieve a cooling rate of up to 100 °C / s, while a twin-roll caster can achieve a cooling rate of up to 1000 °C / s. Rapid cooling and relatively low solidification rates help reduce the formation of large precipitates that hinder the subsequent fabrication of parts from the resulting sheets.

[0019] In some embodiments, the target alloy composition may be 2.5 to 4.5 wt% Mg and 0.6 to 1.6 wt% Si, which requires a lower-tonnage machine for twin-roll / dual-belt processing, as high alloying levels harden the Al alloy during deformation. The composition of the other elements may be between 0.20 wt% and 0.35 wt% Fe, 0.05 wt% and 0.15 wt% Cr, up to 0.4 wt% Mn, up to 0.1 wt% Cu, and up to 0.1 wt% Zn. Lower amounts of Fe, Mn, and Cr may help reduce the volume of brittle intermetallic particles formed. The inventors have found that the amount and relative proportion of Mg and Si can affect the solidification range. Through thermodynamic studies, the inventors have determined that it may be advantageous if the Si and Mg content satisfies this relationship: Si wt% > 0.5 * Mg wt% - 0.65 wt%, and in other embodiments this relationship is satisfied: Si wt% > 0.5 * Mg wt% - 0.35 wt%).

[0020] After the initial sheet production, it can undergo various processing steps to improve its formability. For example, the cast sheet can be hot rolled, the hot-rolled sheet annealed, the annealed sheet cold rolled, and the cold-rolled sheet annealed. An alternative process could involve homogenizing the cast sheet, cold rolling the homogenized sheet, and annealing the cold-rolled sheet.

[0021] A second embodiment of this disclosure provides aluminum sheet material made with significant amounts of secondary aluminum, thereby reducing energy consumption and CO 2emissions, yet is still suitable for producing large parts for commercial and consumer goods, such as automotive parts. Although even minimal use of secondary aluminum reduces energy consumption and CO 2 emissions, the aluminum sheet material in some embodiments comprises at least 30% secondary aluminum from scrap and recycling streams and in other embodiments at least 60% secondary aluminum, and it is possible to comprise up to 100% secondary aluminum.

[0022] According to this second embodiment, this aluminum sheet may have a composition consisting essentially of 2.5 wt% to 6.3 wt% Mg, 0.6 wt% to 2.5 wt% Si, 0.2 wt% to 0.4 wt% Fe, 0.05 wt% to 0.2 wt% Cr, up to 0.6 wt% Mn, up to 0.2 wt% Cu, up to 0.2 wt% Zn, the remainder being Al and unavoidable impurities, wherein the silicon and magnesium contents satisfy the relationship (Si wt% > 0.5 * Mg wt% - 0.65 wt%). This composition includes various alloying elements derived from scrap and recycled material streams and can still be formed into sheets using the continuous casting process. This composition allows for a significant proportion of secondary aluminum (at least 30%) and can easily contain 60% or more secondary aluminum, depending on the quantity and composition of the available scrap and recycled aluminum.

[0023] In some embodiments, the composition of the sheet is 2.5 wt% to 4.5 wt% Mg and 0.6 wt% to 1.6 wt% Si, and 0.25 wt% to 0.35 wt% Fe, 0.1 wt% to 0.15 wt% Cr, up to 0.4 wt% Mn, up to 0.2 wt% Cu, and up to 0.2 wt% Zn.

[0024] The sheet can be cast using either a twin-roll continuous caster or a dual-belt caster. A dual-belt caster can achieve a cooling rate of up to 100 °C / s, while a twin-roll continuous caster can achieve a cooling rate of up to 1000 °C / s. Rapid cooling and relatively low solidification rates help reduce the formation of large precipitates that hinder the subsequent manufacture of parts from the resulting sheet.

[0025] A third embodiment of this disclosure provides an aluminum alloy composition specifically suited for use in manufacturing processes involving aluminum from secondary sources. The composition is tolerant to alloying elements introduced by the scrap and recycled aluminum and has a sufficiently low solidification range (e.g., below 100°C and, in some cases, below about 85°C) to enable forming with continuous casting technologies such as twin-roll casters or twin-belt casters.

[0026] The alloy may have a composition comprising from 2.5 wt% to 6.3 wt% Mg, from 0.6 wt% to 2.5 wt% Si, from 0.2 wt% to 0.4 wt% Fe, from 0.05 wt% to 0.2 wt% Cr, up to 0.6 wt% Mn, up to 0.2 wt% Cu, up to 0.2 wt% Zn, with the remainder being Al and unavoidable impurities, wherein the silicon and magnesium contents satisfy the relationship (Si wt% > 0.5 * Mg wt% - 0.65 wt%). In other embodiments, the composition may comprise 2.5 wt% to 4.5 wt% Mg and 0.6 wt% to 1.6 wt% Si. The composition can be between 0.20 wt% and 0.30 wt% Fe, 0.05 wt% to 0.15 wt% Cr, up to 0.4 wt% Mn, up to 0.1 wt% Cu and up to 0.1 wt% Zn.

[0027] The inventors have discovered that the amount and relative proportion of Mg and Si can affect the solidification range. Through thermodynamic studies, it may be desirable for the Si and Mg content to satisfy this relationship: Si wt% > 0.5 * Mg wt% - 0.65 wt%, and greater satisfy this relationship: Si wt% > 0.5 * Mg wt% - 0.35 wt%. The composition can be selected to have a solidification range of less than 100°C, and in some embodiments, less than 85°C. In some embodiments, the solidification is selected to be less than or equal to the cooling rate per second of the continuous casting system, and in some embodiments, even ten times less than the cooling rate per second of the continuous casting system.

[0028] Since the alloy is made with a significant amount of aluminum scrap and recycled aluminum, it may include other elements in amounts that do not significantly affect the relevant properties of the alloy for producing quality aluminum sheet, as other elements such as titanium, vanadium and strontium may also be included without departing from the principles of this disclosure, provided that its solidification range and castability using continuous casting technology, its formability into parts and the mechanical strength of these parts are not adversely affected.

[0029] The alloy generally has a microstructure consisting of an Al matrix with fragmented and spherodized Mg 2 Si particles and some block-shaped Al-(Cr, Fe, Mn)-Si particles.

[0030] The alloy is particularly suitable for the production of aluminum sheets by continuous casting, especially on twin-roll and twin-belt continuous casting machines. These sheets, in turn, are suitable for forming parts, e.g., through hot forming, such as hot stamping, to produce deep-drawn parts and parts with complex geometries.

[0031] The foregoing description is for purposes of illustration only and is in no way intended to limit the disclosure, its application, or uses.

[0032] The broad teachings of the disclosure may be embodied in a variety of forms. Although this disclosure includes particular examples, the true scope of the disclosure should not be limited thereby, since other modifications will become apparent upon study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be performed in a different order (or simultaneously) without changing the principles of the present disclosure. Although each of the embodiments described above includes certain features, one or more of those features described with respect to any embodiment of the disclosure may be implemented in any other embodiment and / or combined with features of any other embodiment, even if that combination is not expressly described.In other words, the described embodiments are not mutually exclusive, and combinations of one or more embodiments with each other remain within the scope of this disclosure.

[0033] Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaging," "coupled," "adjacent," "adjacent," "on top of," "above," "below," and "disposed." When a relationship between a first and a second element is not explicitly described as "direct" in the above disclosure, that relationship may be a direct relationship, where no other intervening elements are present between the first and second elements, or it may be an indirect relationship, where one or more intervening elements (either spatial or functional) are present between the first and second elements.As used herein, the phrase "at least one of A, B, and C" should be understood as logical (A OR B OR C) using a non-exclusive logical OR, and not as "at least one of A, at least one of B, and at least one of C."

Claims

[1] A method for producing aluminum sheet material, comprising the steps of: Melting of secondary aluminum; Adding primary aluminum and other alloying elements to the melt to achieve a composition consisting essentially of 2.5 wt% to 6.3 wt% Mg, 0.6 wt% to 2.5 wt% Si, 0.2 wt% to 0.4 wt% Fe, 0.05 wt% to 0.2 wt% Cr, up to 0.6 wt% Mn, up to 0.2 wt% Cu, up to 0.2 wt% Zn, the remainder being Al and unavoidable impurities, wherein the Si and Mg contents satisfy the relationship (Si wt% > 0.5 * Mg wt% - 0.65 wt%); and Continuous casting of aluminum into aluminum sheet. [2] A method for producing aluminum sheet material according to claim 1, wherein the composition comprises 2.5 wt% to 4.5 wt% Mg and 0.6 wt% to 1.6 wt% Si. [3] A method for producing aluminum sheet according to claim 2, wherein 0.20 wt% to 0.30 wt% of Fe, 0.05 wt% to 0.15 wt% of Cr, up to 0.4 wt% of Mn, up to 0.1 wt% of Cu and up to 0.1 wt% of Zn are included. [4] A method for producing aluminum sheet material according to claim 1, wherein the continuous casting is carried out using a twin-roll continuous caster. [5] A method for producing aluminum sheet material according to claim 1, wherein the continuous casting is carried out using a twin-belt continuous caster. [6] A method of manufacturing aluminum sheet material according to claim 1, further comprising hot rolling the cast sheet, annealing the hot rolled sheet, cold rolling the annealed sheet, and annealing the cold rolled sheet. [7] A method of manufacturing aluminum sheet material according to claim 1, further comprising homogenizing the cast sheet, cold rolling the homogenized sheet, and annealing the cold rolled sheet. [8] Aluminum sheet material continuously cast from an alloy consisting essentially of 2.5 wt% to 6.3 wt% Mg, 0.6 wt% to 2.5 wt% Si, 0.2 wt% to 0.4 wt% Fe, 0.05 wt% to 0.2 wt% Cr, up to 0.6 wt% Mn, up to 0.2 wt% Cu, up to 0.2 wt% Zn, the balance being Al and unavoidable impurities, the Si and Mg contents satisfying the relationship (Si wt% > 0.5 * Mg wt% - 0.65 wt%). [9] The aluminum sheet material according to claim 8, wherein the composition of the alloy is from 2.5 wt% to 4.5% Mg and from 0.6 wt% to 1.6% Si. [10] The aluminum sheet material according to claim 9, wherein the composition of the alloy is 0.20 wt% to 0.30 wt% Fe, 0.05 wt% to 0.15 wt% Cr, up to 0.4 wt% Mn, up to 0.1 wt% Cu, and up to 0.1 wt% Zn.

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