Patent Application
20210010109
The present invention generally related to an improved aluminum 6XXX alloy extrusion component with high strengths and energy absorption.
The automotive industry is continuously looking at means to lightweight components in an effort to improve fuel efficiency and meet CAFE (corporate average fuel economy) standards. Simultaneously there is a desire to continuously improve the safety rating of the vehicle with designs and materials that absorb the energy from a crash without transmitting it to the driver or passengers. Aluminum extrusions have been used to achieve these goals for years, but lower strength alloys had to be utilized in certain applications where energy absorption without fracture of the material was required. Higher strength aluminum alloys enable additional fuel efficiency improvements in these applications by allowing thinner sections with reduced cross sectional areas. These alloys, properly processed, provide the energy absorption and fracture performance necessary to attain safety requirements.
The present invention is an improved aluminum 6XXX alloy extrusion component with high strengths and energy absorption produced from an alloy composition including, in weight percent, Si: 0.50-0.80; Fe: <0.40; Cu: 0.15-0.35; Mn: 0.20-0.50; Mg: 0.50-0.80; Cr: 0.10-0.25; Zn: <0.20; with other elements being considered incidental impurities and consisting of less than 0.05 individually and 0.15 in total with the balance being aluminum. In a preferred embodiment, the alloy composition does not require any additions of vanadium, thus reducing cost and also preventing contamination of the recycling scrap stream.
The features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, in which:
The present invention is an aluminum 6XXX alloy extrusion component produced from an alloy composition comprising, optionally consisting essentially of, or optionally consisting of, in weight percent (wt. %): Si: 0.50-0.80; Fe: <0.40; Cu: 0.15-0.35; Mn: 0.20-0.50; Mg: 0.50-0.80; Cr: 0.10-0.25; Zn: <0.20; with other incidental elements being considered impurities and consisting of less than 0.05 individually and 0.15 in total with the balance being aluminum. In one embodiment of the present invention, the alloy composition does not include any intentional additions of vanadium. In one embodiment, the alloy composition includes ≤0.04 wt. % vanadium. It should be understood that the recitation of a range of values includes all of the specific values in between the highest and lowest value.
Silicon is included in the alloy composition of the present invention in the range of 0.50 to 0.80 wt. %. It is understood that within the range of 0.50 to 0.80 wt. % Si, the upper or lower limit for the amount of Si may be selected from 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, and 0.80 wt. % Si.
In addition to the amounts of silicon provided above, iron may be included in the alloy composition of the present invention in an amount that is <0.40 wt. %. It is understood that within the range of <0.40 wt. %, the upper or lower limit for the amount of Fe may be selected from 0.40, 0.39, 0.38, 0.37, 0.36, 0.35, 0.34, 0.33, 0.32, 0.31, 0.30, 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, and 0.01 wt. %.
In addition to the amounts of silicon and iron provided above, copper may be included in the alloy composition of the present invention in the range of 0.15-0.35 wt. %. It is understood that within the range of 0.15-0.35 wt. %, the upper or lower limit for the amount of Cu may be selected from 0.35, 0.34, 0.33, 0.32, 0.31, 0.30, 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, and 0.15 wt. %.
In addition to the amounts of silicon, iron, and copper provided above, manganese may be included in the alloy composition of the present invention in the range of 0.20-0.50 wt. %. It is understood that within the range of 0.20-0.50 wt. %, the upper or lower limit for the amount of Mn may be selected from 0.50, 0.49, 0.48, 0.47, 0.46, 0.45, 0.44, 0.43, 0.42, 0.41, 0.40, 0.39, 0.38, 0.37, 0.36, 0.35, 0.34, 0.33, 0.32, 0.31, 0.30, 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, 0.23, 0.22, 0.21, and 0.20 wt. %.
In addition to the amount of silicon, iron, copper, and manganese provided above, magnesium may be included in the alloy composition of the present invention in the range of 0.50 to 0.80 wt. %. It is understood that within the range of 0.50 to 0.80 wt. % Mg, the upper or lower limit for the amount of Mg may be selected from 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, and 0.80 wt. %.
In addition to the amounts of silicon, iron, copper, manganese, and magnesium provided above, chromium may be included in the alloy composition of the present invention in the range of 0.10-0.25 wt. %. It is understood that within the range of 0.10-0.25 wt. %, the upper or lower limit for the amount of Cr may be selected from 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, and 0.10 wt. %.
In addition to the amounts of silicon, iron, copper, manganese, magnesium, and chromium provided above, zinc may be included in the alloy composition of the present invention in an amount that is <0.20 wt. %. It is understood that within the range of <0.20 wt. %, the upper or lower limit for the amount of Zn may be selected from 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, and 0.01 wt. %.
In addition to the amounts of silicon, iron, copper, manganese, magnesium, chromium, and zinc provided above, it is understood that vanadium is not intentionally added to the alloy composition of the present invention. Vanadium may exist in the alloy composition of the present invention as a result of a non-intentionally added element. In one embodiment, the alloy composition of the present invention includes ≤0.04 wt. % vanadium. It is understood that within the range of <0.04 wt. %, the upper or lower limit for the amount of V may be selected from 0.04, 0.03, 0.02, 0.01, and 0.005 wt. %
In addition to the amounts of silicon, iron, copper, manganese, magnesium, chromium, zinc, and vanadium, Sn may be intentionally added within the range of 0.02-0.10% by weight to improve adhesive bond durability performance. It is understood that within the range of 0.02-0.10 wt. %, the upper or lower limit for the amount of Sn may be selected from 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, and 0.02 wt. %.
In addition to the amounts of silicon, iron, copper, manganese, magnesium, chromium, zinc, vanadium, and tin, Sr may be intentionally added within the range of up to 0.30% by weight. It is understood that within the range of up to 0.30 wt. %, the upper or lower limit for the amount of Sr may be selected from 0.30, 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, and 0.01 wt. %.
The alloy composition of the present invention may also include low level of “incidental elements” that are not included intentionally. The “incidental elements” means any other elements except the above described Al, Si, Fe, Cu, Mn, Mg, Cr, Zn, Sn, Sr and V.
The alloy composition may be used to produce an automotive crush can, front rail, rear rail, upper rail, rocker, header, A-pillar, or roof rail.
The extrusion component may be produced by i) homogenizing a billet including the present alloy composition at a billet temperature between 527-566° C., ii) followed by fan cooling, iii) followed by either a) extruding at a billet temperature of 455° C. to 510° C. orb) heating to a billet temperature of 491° C.-535° C., then water quenching to a billet temperature of 388° C.-496° C., and then extruding, and iv) followed by cold water quenching, stretching and artificial aging with the extrusion component having a specific energy absorption of greater than 22 kJ/mm2 and a yield strength of greater than 260 MPa, or 280 MPa, while providing no fragmentation or surface cracks greater than 10 mm during defined crush testing (as defined herein). In an alternate embodiment, the end product has a specific energy absorption of greater than 22 kJ/mm2 and a yield strength of greater than 280 MPa, while providing no fragmentation or surface cracks greater than 20 mm during defined crush testing (as defined herein). In another alternate embodiment, the end product has a specific energy absorption of greater than 22 kJ/mm2 and a yield strength of greater than 300 MPa, while providing no fragmentation or surface cracks greater than 30 mm during defined crush testing (as defined herein). The superior combination of strength and energy absorption for crash management applications is a basic and novel characteristic of the present invention.
The crash worthiness of an automotive component is typically assessed by the amount of energy absorbed in a crush test, without having any unacceptable fracturing of the component. “Crush testing” as used herein is conducted by taking a 300 mm long sample and crushing in the longitudinal direction to 100 mm at a rate of 100 mm/minute. The force required through the stroke of the crush testing is recorded and the area under the force displacement curve is the energy absorption. Once the crush testing is complete, the sample is visually examined for fractures and surface cracking. Fractures resulting in fragmentation are not acceptable and surface cracks are not desirable, but may be acceptable for certain applications provided they are not too severe. Surface cracks are typically limited to a maximum observable length, perhaps 10 mm, or 20 mm, or 30 mm. For some applications longer surface cracks may be deemed acceptable with a corresponding increase in yield strength or energy absorption. A sample that does not pass the visual examination, however, is considered a failed sample, regardless of the energy absorbed. Thus the visual examination is a binary, pass/fail assessment. Samples passing the visual examination can thus be compared quantitatively relative to the energy absorption. This is the crush testing basis for all results reported herein.
Energy absorption is not exclusively a material property. There is a shape design component as well. Clearly the greater the cross sectional area, the greater the energy required to crush a component with a given strength level. This can be overcome by providing a specific energy absorption, determined by dividing the energy absorbed by the extruded component's cross sectional area. This still does not define an absolute material property, as there are mechanical advantages of some shape designs that predispose their ability to absorb more energy than other designs for a given material. In order to overcome these difficulties and provide an assessment of the material, the energy absorption is expressed as specific energy absorption (energy absorbed/cross sectional area) and is limited to a common crash management component design, which for the purposes of this study, is a three void hollow extrusion with wall thicknesses from 1.5 mm to 4 mm and a rectangular or trapezoidal perimeter being 75 mm to 175 mm in the long direction and 40 mm to 100 mm in the shorter direction as shown in
Aluminum extrusions have been utilized in the construction of crash management systems for many years. Successfully attaining a component that absorbs energy without fracture, that could threaten injury to passengers, involves complex management of the composition, grain structure, precipitate structure and mechanical properties. The composition of the extrusions helps to determine the potential strength. In 6XXX alloys under the present invention, precipitation hardening occurs with Mg—Si phases (Mg2Si). The proportion of the Mg and Si (in terms of being balanced, excess Si or excess Mg relative to the stoichiometry) can significantly influence the strength and crush performance as well. The Mg and Si are often assessed in these terms:
Mg/Si Ratio; Calculated by: Mg/(Si−(0.25(Fe+Mn)))
Excess Si; Calculated by: Si−((0.58 Mg)+(Fe+Mn)/4)
Mg2Si Content; Calculated by:
Thus control of processes such as homogenization, billet temperature, use of billet quenches, extrusion die design, extrusion speed and quench rate post extrusion all play a critical role in the final achieved grain size in the product. Extrusion of the product can be accomplished by either a) heating the billet directly to the extrusion temperature or b) using a process referred to as super-heating, where the billet is heated beyond the desired extrusion temperature to facilitate the solutionizing of hardening phases, and is then rapidly quenched to desired extrusion temperature. Both billet heating strategies have been employed successfully in this work. Post extrusion, the material is artificially aged to increase its strength. The artificial age time and temperature can strongly influence the size, distribution of the precipitate particles, and even precipitation type in the matrix, which not only affects the potential strength, but can also significantly impact the energy absorption and crash worthiness of the component. Artificial aging can be delayed to provide an extrusion that has better formability, with the artificial aging cycle being conducted after the component is formed. In one embodiment, the artificial aging is conducted at billet temperatures between 174-191° C. for 5-10 hours. The artificial aging can also include multi-step aging to improve corrosion resistance. The artificial aging may be a two-step age cycle with the second aging step being hotter than the first aging step and either aging step ranging between 100-204° C. In one embodiment, the two-step age cycles involve a lower temperature step 1 from 100-177° C. and a second step from 172-204° C. The artificial aging can also intentionally be under-aged (less than peak strength), with the intention of subsequent thermal operations, such as paint baking, completing the remainder of the artificial aging cycle. Alternatively, the component is unaged (T4) to provide better formability of the component with artificial aging being conducted post forming.
All of these factors must be balanced in order to meet multiple objectives simultaneously. In the case of the present invention, for example, that is an automotive crash management component with high yield strength and excellent energy absorption without exhibiting a tendency for fragmentation. This is achieved with a predominantly unrecrystallized extruded grain structure in a 6XXX (Al—Mg—Si alloy) hollow extruded material. In a preferred embodiment, the coarse surface grain depth is controlled to less than 0.5 mm in depth from the surface.
The following examples illustrate various aspects of the invention and are not intended to limit the scope of the invention.
Most incumbent alloy compositions used for crash management systems have lower strengths and few dispersoids elements (like Cr and Mn). These alloys include 6060 and 6063 for example. The fine recrystallized structure attainable in these alloys is known to be preferable for formability and crush applications, although it does not provide the higher strength levels of other alloys (for example 6082). Alloy 6063 has a typical yield strength of 214 MPa and when tested using the crush test procedures outlined above, only has an energy absorption of 19.468 kJ/mm2. In an effort to increase the strength and determine the influence of Cr as a dispersoid element the compositions in Table 1 were cast, homogenized between 980° F. and 1060° F. (527° C.-566° C.) and then forced air cooled. Billets from the logs were preheated to 880° F. to 940° F. (471° C.-504° C.), extruded into the three void hollow shape of
The grain structure of the materials is shown in
The composition shown in Table 2 was cast into 10″ (254 mm) diameter log using development scale equipment.
The logs were homogenized between 980° F. and 1060° F. (527° C.-566° C.) and then forced air cooled. The billets were then extruded into the three void hollow shape of
From both of these extrusion runs, the crash worthiness was assessed with 100 individual tests throughout the extrusion run. The statistics of these tests for the specific energy absorption are shown in Table 4. The energy absorption along the length of the extrusion billet is also shown in
The qualitative visual examination of these tests were all deemed to be acceptable, meeting the criteria for the tests to be considered acceptable with no fragmentation or excessive cracking. In addition to this, the extrusion process parameters were deemed to be acceptable in terms of providing consistent results along the extruded length as demonstrated in
Extrusion billet was produced using conventional direct chill casting methods in 10″ (254 mm) diameter log using production scale equipment to validate reproducibility. The composition of this material is shown in Table 5.
The logs were homogenized between 980° F. and 1050° F. (527° C.-566° C.) and then forced air cooled. The billets were then extruded into the three void hollow shape of
Samples from the artificially aged material were then tested for crush quality and energy absorption. All samples passed the visual examination criteria. The specific energy absorption from this testing is shown in Table 7.
These results demonstrate the repeatability of the process and compatibility to production scale processes.
The compositions shown in Table 8 were cast and extruded as per the previous examples.
The logs were homogenized between 980° F. and 1060° F. (527° C.-566° C.) and then forced air cooled. The billets were then extruded into the three void hollow shape of
Samples from all of these materials were tested for mechanical properties and tested for energy absorption and crash worthiness. The results of this are shown in Tables 9 and 10 and graphically in
The specific energy absorption increases with increasing yield strength and thus the results show that as the amount of solute (as expressed in terms of Mg+Si+Cu) the strength and specific energy absorption increases.
While these results would suggest that specific energy absorption could be improved even further with additional solute additions (along with yield strength), it must be noted that with increasing mechanical properties, the susceptibility of the material failing from a surface cracking perspective increases.
Extrusion billet was produced using conventional direct chill casting methods in 10″ (254 mm) diameter log using production scale equipment to validate reproducibility. The composition of this material is shown in Table 11. The logs were homogenized between 980° F. and 1050° F. (527° C.-566° C.) and then forced air cooled.
Complex extruded shapes can be sensitive to quench rates from the extrusion operation. Faster quench rates can result in dimensional distortion that is considered unacceptable for the final application. It is generally accepted that faster quench rates provide higher strengths and better resistance to surface cracking during crush testing. In an effort to determine the alloy sensitivity to quench rate, the three void hollow shape of
While the average ultimate and yield strength were slightly lower at the lowest water flow rates studied, the alloy proves to be surprisingly robust relative to quench sensitivity from an energy absorption perspective.
Complex extruded shapes may be restricted in terms of extrusion speed, with more complex shapes being restricted to slower extrusion speeds than other shapes. More complex shapes also may require greater extrusion force. In some cases, the extrusion force may exceed the capability of the extrusion press and thus higher billet temperatures are required to enable extrusion of the more complex shapes. In order to assure the alloy was robust in providing consistent mechanical properties and energy absorption with these known potential process variations, billet produced in the same batch of material as in example 5 was extruded into the three void hollow shape depicted in
The consistency in mechanical properties and energy absorption shows that this material is also insensitive to both billet temperature variation and extrusion rates.
While specific embodiments of the invention have been disclosed, it will be appreciated by those skilled in the art that various modifications and alterations to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth if the appended claims and any and all equivalents thereof.
This application claims the benefit, under 35 USC 119(e), of U.S. Provisional Application No. 62/872,384 filed Jul. 10, 2019, the contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62872384 | Jul 2019 | US |
