Manufacturing process for a wear-resistant aluminum alloy sheet product

Abstract

A manufacturing process for a wear-resistant aluminum alloy rolled product comprising the following steps: (a) provide a raw material of an aluminum alloy having a composition comprising, in % by weight, Mg from 4.20% to 5.5% Mn from 0.50% to 1.1% Fe up to 0.40% Yes, up to 0.30% Cu up to 0.20% Cr up to 0.25% Zr up to 0.25% Zn up to 0.30% Ti up to 0.25% unavoidable impurities, individually at most 0.05%, in total at most 0.02%, and the rest is aluminum; (b) heating the rolling raw material to a temperature ranging between 475 °C and 535 °C; (c) hot rolling the raw material in one or more rolling stages to achieve an intermediate gauge between 15 mm and 40 mm, preferably between 15 mm and 30 mm, and where preferably the outlet temperature of the rolling mill varies between 370 °C and 495 °C; (d) hot rolling the raw material from an intermediate gauge in one or more rolling stages to a final gauge between 3 mm and 15 mm, wherein the average temperature of the hot-rolled raw material when the raw material is introduced into process stage (d) is maintained in a range of 370 °C to 495 °C, wherein the outlet temperature of the rolling mill varies between 130 °C and 285 °C, and wherein after hot rolling to the final gauge, the process has no cold rolling stage(s); (e) cooling the hot-rolled raw material to the final gauge from the rolling mill outlet temperature to ambient temperature, wherein after hot-rolling the raw material to the final gauge and after cooling to ambient temperature, the aluminum alloy product is not subjected to any further heat treatment.

Description

Manufacturing process for a wear-resistant aluminum alloy sheet product FIELD OF INVENTION The invention relates to a manufacturing process for a wear-resistant Al-Mg-Mn sheet product. The sheet material can be used, for example, to manufacture truck bed liners. BACKGROUND OF THE INVENTION Wear- or abrasion-resistant aluminum alloy sheet materials for dump truck or pickup truck bodies are commonly manufactured from Al-Mg-Mn alloys such as AA5456, AA5083, and AA5383, and are supplied in an H32 temper and, more preferably, an H34 temper. The designation H3x, where "x" is selected from 1 to 11, requires that the aluminum material in question has been at least hot-rolled, subsequently cooled to room temperature, optionally inter-annealed, work-hardened by cold rolling, and subjected to a final annealing heat treatment. At least the final annealing heat treatment is a separate batch thermal process in which the coils are placed in a furnace or heater maintained at a temperature sufficient to induce the recovery or final mechanical properties.This batch thermal operation requires that the coils be heated for several hours to the correct temperature, after which they are typically cooled to room temperature. The compositional ranges of these aluminum alloys are listed in Table 1. Table 1. Alloy compositions (in % by weight) of AA5456, AA5083 and AA5383, where the remainder is made up of impurities, individually at most 0.05%, in total at most 0.15%, and the remainder is aluminum. European patent application EP 0799900 describes an alloy that has substantially improved strength in both soft and hard tempering compared to the well-known alloy AA5083 used in the manufacture of storage containers and marine and land transport vehicles such as silos and tank trucks, etc. It is an objective of the invention to provide a manufacturing process for an Al-Mg-Mn alloy sheet product that offers a good balance of wear resistance, strength, and pliability. It is another objective of the invention to provide an alternative manufacturing process for an Al-Mg-Mn alloy sheet product compared to the H3x production route. DESCRIPTION OF THE INVENTION As will be seen below in this document, unless otherwise stated, the aluminum alloy and temper designations refer to the designations of the Aluminum Association in the Aluminum Standards and Data and Registration Records, as published by the Aluminum Association in 2016 and well known to experts in the field. Regarding the description of alloy compositions or preferred alloy compositions, all references to percentages are in weight percent unless otherwise stated. The terms "up to" and "up to approximately," as used herein, explicitly include, but are not limited to, the possibility that the weight percent of the particular alloying component referred to may be zero. For example, up to 0.1% Zn may include an alloy that does not contain Zn. As used herein, the term "approximately" when employed to describe a compositional range or amount of an alloying addition means that the actual amount of the alloying addition may vary from the nominal amount anticipated due to factors such as standard processing variations as understood by those skilled in the art. This and other objectives and advantages are met or exceeded by the present invention, which provides a manufacturing process for a wear-resistant aluminum alloy rolled product, ideally for use in dump trucks or dump truck bodies, comprising the following steps: (a) provide a rolling raw material of an aluminum alloy having a composition comprising, in % by weight, Mg 4.20% to 5.5% Mn 0.50% to 1.1% Fe up to 0.40%, preferably up to 0.30% If up to 0.30%, preferably up to 0.20%. Cu up to 0.20%, preferably up to 0.1% Cr up to 0.25% Zr up to 0.25% Zn up to 0.30%, preferably up to 0.1% Ti up to 0.25%, preferably from 0.005% to 0.10%, unavoidable impurities, individually at most 0.05%, in total at most 0.02%, and the rest is aluminum; (b) heating the rolling raw material to a temperature between 475 °C and 535 °C; optionally, a separate homogenization treatment is carried out before heating the rolling raw material to said temperature range; (c) hot rolling the raw material in one or more rolling stages to achieve an intermediate gauge between 15 mm and 40 mm, preferably between 15 mm and 30 mm, and where preferably the outlet temperature of the rolling mill varies between 370 °C and 495 °C; (d) hot rolling the raw material from an intermediate gauge in one or more rolling stages to a final gauge between 3 mm and 15 mm, wherein the average temperature of the hot-rolled raw material when the raw material is introduced into the process stage (d) is maintained in the range of 370 °C to 495 °C, wherein the outlet temperature of the rolling mill varies between 130 °C and 285 °C, and wherein after hot rolling to the final gauge, the process has no cold rolling stage(s); and (e) cooling, preferably by air, the hot-rolled raw material with the final gauge from the rolling mill outlet temperature to ambient temperature, wherein after hot-rolling the raw material to the final gauge and after cooling to ambient temperature, the aluminum alloy product is not subjected to any further heat treatment, and is stored. The cooled raw material, now at its final thickness, is suitable for finishing operations such as leveling to improve product flatness, edge trimming, slitting, and custom cutting. Optionally, a recovery annealing process can be applied. The process according to the present invention allows for the manufacture of Al-Mg-Mn sheet products having a tensile strength of at least 215 MPa, a tensile breaking strength of at least 320 MPa, and a hardness of at least 100 HB. The process according to the present invention also allows for the manufacture of Al-Mg-Mn sheet products with very good wear resistance. Furthermore, the process allows for the manufacture of Al-Mg-Mn sheet products with very good foldability, in particular achieving bend angles greater than 90° with bend radii of 3.5 times, and preferably 3 times, the material thickness. Foldability is an important parameter, as it allows for the molding or forming of products using the Al-Mg-Mn sheet into specific shapes without the need for welding. These properties are achieved through a more efficient manufacturing process, as no cold rolling of the raw material is required to obtain a smaller gauge. Nor is any final annealing heat treatment, particularly batch annealing, necessary after a cold rolling operation, as required in the prior art to obtain an H3x temper such as H32 and H34. The process of the present invention can be implemented more economically to provide a sheet product with equivalent or superior metallurgical properties. The Al-Mg-Mn alloy can be supplied as an ingot or block for manufacturing rolling raw material using common casting techniques for cast products, such as direct cooling, electromagnetic field casting, and electromagnetic stirring casting, preferably with an ingot thickness of approximately 220 mm or more, such as 400 mm, 500 mm, or 600 mm. Alternatively, small-gauge blocks resulting from continuous casting, such as from strip or roll molders, and having a thickness of up to approximately 40 mm, can also be used. After casting the rolling raw material, the freshly cast thick ingot is typically descaled to remove segregation zones near the cast surface. Preheating prior to hot rolling is carried out at a temperature ranging from 475 °C to 535 °C. In any case, preheating reduces the segregation of alloying elements in the freshly cast material. Zr, Cr, and Mn can be intentionally precipitated in multiple stages to control the microstructure of the raw material exiting the rolling mill. If the treatment is carried out below approximately 475 °C, the resulting homogenization effect is inadequate. If the temperature exceeds 535 °C, eutectic melting may occur, leading to undesirable porosity. The preferred preheating time ranges from 1 to 24 hours, for example, 8 hours or 18 hours. Hot rolling preferably begins at a temperature above 500 °C. In a first hot rolling operation, the heated raw material undergoes partial hot rolling in one or more passes using reversible or non-reversible rolling mill stands to reduce the thickness of the raw material to a gauge range of 15 to 40 mm, and preferably 15 to 30 mm, and more preferably 15 to 25 mm. The partial rolling preferably begins at a temperature of 500°C or higher. Preferably, the hot rolling process temperature should be controlled so that, after the last rolling pass, the exit temperature of the raw material from the rolling mill ranges between 370°C and 495°C. A more preferred lower limit is 400°C. A more preferred upper limit is 465°C. Following partial hot rolling, the raw material is fed to a hot finishing mill in one or more passes to achieve a final thickness ranging from 3 to 15 mm, for example, 7 mm or 10 mm. The hot finishing operation can be carried out, for example, using a reversing mill or a tandem mill. Generally, the thickness of the cast raw material is typically reduced (considering processing steps (c) and (d) together) by at least 65%, and more typically between 80% and 99%. The average temperature of the hot-rolled raw material when it enters processing step (d) is maintained in the range of 370 °C to 495 °C. A more preferred lower limit is 400 °C. A more preferred upper limit is 465 °C. It is important to control the exit temperature of the rolled raw material from the rolling mill to achieve the desired balance of metallurgical properties. The rolling mill temperature should be controlled so that, after the last rolling pass, the exit temperature of the raw material is between 130 °C and 285 °C. A preferred lower limit is 150 °C, and more preferably 175 °C. A preferred upper limit is 275 °C, and more preferably 250 °C, and more preferably 235 °C. At an exit temperature that is too low for the raw material, the strength and hardness of the final product will be excessively high, negatively affecting its pliability. An exit temperature that is too low can also negatively affect the coiling performance of the raw material during the rolling operation, as well as during the subsequent finishing operation.On the other hand, at excessively high outlet temperatures, at least the solidity and hardness of the raw material will be too low and will offer an unfavorable balance of properties. After the final hot rolling stage, the hot-rolled raw material with the final gauge is cooled to ambient temperature. In a preferred embodiment, the cooling of the hot-rolled raw material with the final gauge from the rolling mill outlet temperature to ambient temperature during process step (e) is carried out by immediately winding the hot-rolled raw material and allowing it to cool in an ambient temperature environment, and then storing it. Careful control of the hot rolling process and cooling to room temperature results in an Al-Mg-Mn sheet product with a completely non-recrystallized microstructure that provides the required balance of properties, including wear and abrasion resistance. The term "completely non-recrystallized" means that the degree of recrystallization of the microstructure does not exceed 25%, preferably not exceed 20%, and more preferably not exceed 10%. In the aluminum alloy product manufactured according to the process of the invention, the Mg content ranges from 4.20% to 5.5% and forms the main reinforcing element of the alloy. A preferred lower limit for the Mg content is 4.6%, and more preferably 4.75%, to provide greater wear resistance. A preferred upper limit for the Mg content is 5.3%. The manganese content ranges from 0.50% to 1.1% and is another essential alloying element. A preferred upper limit for the manganese content is 0.95%, and more preferably 0.85%, to provide a balance of strength and foldability. To control the microstructure of the final product, in addition to the addition of Mn, it is preferable to intentionally add Cr or Zr, each up to 0.25%, as dispersoid-forming elements. A preferred addition of Cr ranges from 0.05% to 0.25%, and more preferably from 0.05% to 0.20%. When Cr is intentionally added, it is preferable that the level of Zr not exceed 0.05%, and preferably be less than 0.02%. Titanium (Ti) is important as a grain refiner during the solidification of both ingots and welded joints produced using the alloy product of the invention. Ti levels should not exceed 0.25%, and the preferred range for Ti is 0.005% to 0.10%. Ti can be added as a single element, or with boron or carbon, which contribute to the casting by controlling the grain size. In one embodiment of the invention, the Al-Mg-Mn alloy consists of, in wt%: Mg 4.20% to 5.5%, Mn 0.50% to 1.1%, Fe up to 0.40%, Si up to 0.30%, Cu up to 0.20%, Cr up to 0.25%, Zr up to 0.25%, Zn up to 0.30%, Ti up to 0.25%, unavoidable impurities, individually at most 0.05%, in total at most 0.02%, and the remainder being aluminum; and narrower compositional ranges are preferred as described and claimed herein. The process according to the present invention allows for the manufacture of Al-Mg-Mn sheet material with a composition as described and claimed herein and with a tensile strength in the LT direction of at least 215 MPa, preferably at least 240 MPa, and more preferably at least 255 MPa. The tensile strength in the LT direction is at least 320 MPa, preferably at least 340 MPa, and more preferably at least 360 MPa. The hardness is at least 100 HB. The wear resistance, measured in a grinding wheel test using an Erichsen-317 test device (ISO 8251), is less than 0.045 g / mm², preferably less than 0.042 g / mm², and more preferably less than 0.040 g / mm². The wear resistance measured by a Taber abrasion wear meter test is less than 0.410 mg / rev, and preferably less than 0.407 mg / rev.The foldability according to the DIN-EN-ISO 7438 standard of the sheet material is that it has folding angles greater than 90° with folding radii of 3, 5 times or more the thickness of the material, and preferably 3 times or more the thickness of the material. The wear-resistant sheet material obtained by the process according to the present invention is ideal for use on floors and / or sides of dump bodies or tipper bodies in trucks and agricultural vehicles, and suitable for bulk transport of a wide variety of products, for example, sand, soil, gravel, bitumen and harvested products such as corn kernels, maize and potatoes. Also described in this document is a dump truck or dump body that incorporates in its floor or sides at least one aluminum alloy sheet product obtained by the process according to the present invention. Also described in this document is the use of an aluminum alloy sheet product obtained by the procedure according to the present invention in a dump truck or dump body, said sheet product being incorporated into its floor or side(s). Figure 1 shows an example of a dump truck with a chassis 2 and a cab 1. The chassis 2 supports a subframe 3. The subframe 3 supports a dump body 4, and a hinge 5 couples the dump body 4 to the subframe 3. In this configuration, the dump body 4 has an overhang 6 at the rear of the hinge 5, so that it extends a distance rearward from the chassis 2. At the rear of the truck, a bumper 8 is provided, and a door 7 closes the dump body 4. Figure 2 shows the dump truck of Figure 1 where the dump body 4 has been tilted. The invention will now be illustrated with reference to non-restrictive embodiments according to the invention. EXAMPLE The sheet product obtained by the process according to the present invention is compared with commercially available sheet products. Alloys No. 1, 2, and 3 are comparison products, and Alloy No. 4 is manufactured according to the present invention. The sheet products of Alloys No. 1, 2, and 3 had thicknesses of 8 mm, 7 mm, and 10 mm, respectively, and all had an H34 temper. The sheet of Alloy No. 4 had a thickness of 7 mm. Table 2 lists the nominal composition of the tested sheet products. Alloy No. 1 is the nominal composition of a commercially available AA5456 alloy. Alloy No. 2 is the nominal composition of a commercially available AA5083 alloy. Alloy No. 3 is the nominal composition of a commercially available AA5383 alloy. Alloy No. 4 is the nominal composition of an alloy used to manufacture a sheet product according to the invention. According to the invention, Alloy No. 4 was cast with direct cooling into a rolling ingot, descaled, and heated for approximately 28 hours at 510°C, which was also the inlet temperature of the rolling mill. It was then rolled on a partial rolling mill to an intermediate gauge of 18 mm and with an outlet temperature of approximately 450°C.Subsequently, it was rolled to 7 mm in a reversing rolling mill using an inlet temperature of 450 °C and an outlet temperature of approximately 230 °C, and immediately wound onto a coil at this temperature for cooling to room temperature. The sheet material had a completely non-recrystallized microstructure. At room temperature, the sheet product was unwound, leveled, and cut to size. Table 2. Alloy compositions, in % by weight, remaining impurities and aluminum. For the four sheet products, the mechanical properties in the LT direction were tested according to DIN EN 10002, where Rm is the tensile strength, R0, 2 is the tensile yield strength, and A is the elongation at break. The results are listed in Table 3. Table 3 lists the wear resistance of the sheet metal products measured according to two test procedures. The grinding wheel wear resistance test was performed using an Erichsen-317 test device (ISO 8251), which includes a grinding wheel covered with abrasive paper that moves back and forth over a test sample under a defined force. The grade of the abrasive paper is defined and the same grade is used for all samples. The weight loss after 10,000 double passes with 60-grit sandpaper is defined and is expressed as mass loss per mm (g / mm) relative to the width of the abrasive paper. In another wear resistance test, the samples were analyzed using a standardized setup according to Taber, where two grinding wheels with a specific surface area rotate with a defined force over a rotating material sample.The two abrasive wheels rotate in opposite directions, meaning that the material is abraded transversely. Weight loss is measured after 2,000 revolutions and is expressed as mass loss per revolution (mg / rev). The test parameters applied were: 60 revolutions / min, 2,000 revolutions (resulting in a sliding distance of 400 m), applied force 10 N, ambient temperature, relative humidity 25%, motion type: rolling, friction track radius: 31.75 mm (U=200 mm), H-18 friction roller. New friction rollers were used for each series of tests. The foldability of all sheet metal products had also been tested according to DIN-EN-ISO 7438. Alloy sheets No. 1, 2, and 3 had bending angles of more than 90° with bending radii of 4, 5 times or more the material thickness, while alloy sheet No. 4 had a bending angle of more than 90° with a bending radius of 3, 5 times the material thickness and, in the best examples, even less than 3. Table 3. Results of mechanical tests (in the LT direction) and wear resistance. From the results in Table 3, it can be seen that the sheet material manufactured according to the invention has mechanical properties similar to or better than the reference material with H34 temper, combined with significantly greater wear resistance. The pliability of alloy No. 4 is also significantly improved, resulting in enhanced formability. With careful control of the hot rolling process, the procedure according to the present invention eliminates the need for any cold rolling operations. Furthermore, the need for any final annealing treatment after a cold rolling operation is also eliminated. The wear-resistant sheet material obtained by the process according to the present invention is ideal for use on floors and / or sides of dump bodies or dump bodies in trucks and agricultural vehicles, and suitable for bulk transport of a wide variety of products. The invention is not limited to the embodiments described above, which can be varied greatly within the scope of the invention as defined in the appended claims.

Claims

1. A process for manufacturing a wear-resistant aluminum alloy rolled product comprising the following steps: (a) providing a rolling raw material of an aluminum alloy having a composition comprising, in wt%, Mg from 4.20% to 5.5%, Mn from 0.50% to 1.1%, Fe up to 0.40%, Si up to 0.30%, Cu up to 0.20%, Cr up to 0.25%, Zr up to 0.25%, Zn up to 0.30%, Ti up to 0.25%, unavoidable impurities, individually not exceeding 0.05%, in total not exceeding 0.02%, and the remainder being aluminum; (b) heating the rolling raw material to a temperature ranging from 475°C to 535°C; (c) hot rolling the raw material in one or more rolling stages to achieve an intermediate gauge between 15 mm and 40 mm, preferably between 15 mm and 30 mm,and wherein preferably the outlet temperature of the rolling mill varies between 370 °C and 495 °C; (d) hot-rolling the raw material from an intermediate gauge in one or more rolling stages to a final gauge between 3 mm and 15 mm, wherein the average temperature of the hot-rolled raw material when the raw material is introduced into process stage (d) is maintained in the range of 370 °C to 495 °C, wherein the outlet temperature of the rolling mill varies between 130 °C and 285 °C, and wherein after hot-rolling to the final gauge, the process has no cold-rolling stage(s); (e) cooling the hot-rolled raw material of the final gauge from the outlet temperature of the rolling mill to ambient temperature, wherein after hot-rolling the raw material to the final gauge and after cooling to ambient temperature,The aluminum alloy product is not subjected to any other heat treatment.

2. A process according to claim 1, wherein the cooling of the hot-rolled raw material of the final gauge from the rolling mill exit temperature to ambient temperature is accomplished by coiling the hot-rolled raw material.

3. A process according to claim 1 or 2, wherein during step (c) the rolling mill exit temperature varies between 400 °C and 465 °C.

4. A process according to any one of claims 1 to 3, wherein during step (d) the rolling mill exit temperature varies between 175 °C and 250 °C.

5. A process according to any one of claims 1 to 4, wherein after cooling to ambient temperature, the cooled raw material of the final gauge is subjected to a finishing operation such as leveling, edge trimming, and slitting.

6. A process according to any one of claims 1 to 5,wherein the aluminum alloy has a Mn content of at most 0.95%, and preferably at most 0.85%.

7. A process according to any one of claims 1 to 6, wherein the aluminum alloy has a Mg content of at least 4.6%, and preferably at least 4.75%.

8. A process according to any one of claims 1 to 7, wherein the aluminum alloy has a Cr content of between 0.05% and 0.20%.

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