Aluminum alloy useful for driveshaft assemblies and method...

Details Aluminum alloy useful for driveshaft assemblies and method... Aluminum alloy useful for driveshaft assemblies and method...

1999-06-04

2001-06-19

Wyszomierski, George (Department: 1742)

Metal treatment

Stock

Age or precipitation hardened or strengthened

C420S546000, C420S534000

Reexamination Certificate

active

06248189

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an aluminum alloy and a method of manufacturing an extruded tube useful as part of a driveshaft assembly of a motor vehicle.
BACKGROUND OF THE INVENTION
Light weight driveshafts and alloys therefor are disclosed in U.S. Pat. Nos. 4,392,839; 4,527,978; 5,320,580; 5,607,524; and 5,637,042. Such driveshafts can be made by various techniques such as machining a solid billet, extruding a solid or hollow billet, seam welding, etc. According to the '524 patent, alloy 6061 has been used for driveshaft applications, the alloy including 0.8-1.2% Mg, 0.4-0.8% Si, 0.15-0.4% Cu, 0.04-0.35% Cr, the balance being Al and incidental impurities. Depending on the type of vehicle, aluminum driveshafts can range from 2 or 3 inches in outside diameter to 4 to 5 inches or even higher, e.g. 6 to 7 inches or higher. Typical wall thicknesses can be 0.05 or 0.06 inch up to about 0.08 or 0.09 inch or even thicker. An example of a driveshaft for an automobile could have an outside diameter of about 3.5 inches and a wall thickness of about 0.08 inch whereas a driveshaft for a truck could have an outside diameter of 4.5 to 5 inches and a wall thickness of 0.07 to 0.09 inch. In order to transmit power, each end of the driveshaft typically includes a yoke welded thereto. The yokes cooperate with universal joints to transmit power from a rotating member to a member to be rotated such as a wheel.
Aluminum-magnesium-silicon extrusion alloys are disclosed in U.S. Pat. Nos. 4,113,472; 4,231,817; 4,256,488; 5,223,050 and 5,240,519. Of these, the '472 patent discloses an alloy including 0.9-1.5% Mg, 0.4-0.8% Si, and 0.9-1.5% Cu. The '817 patent discloses an alloy including 0.45-0.98% Mg, 0.3-0.8% Si and 0.5-0.25% Zn, the alloy optionally including 0.04-0.30% Cu, 0.04-0.25% Zr, 0.04-0.30% Cr and 0.04-0.25% Mn and possibly 0.01-0.20% Ti and/or 0.01-0.06% B. The '488 patent discloses an alloy including 0.030-0.60% Mg, 0.45-0.70% Si and 0.10-0.30% Cu with optional inclusions of up to 0.35% Fe, up to 0.15% Zn and up to 0.010% Ti. The '050 patent discloses 6000 series alloys including 6082, 6351, 6061 and 6063 wherein Mg is present as Mg
2
Si &bgr;′-phase particles. The '519 patent discloses an alloy having 1.0-1.5% Si, 0.4-0.9% Cu, 0.2-0.6% Mn, 0.8-1.5% Mg, 0.3-0.9% Cr, 0.03-0.05% Ti, 0.0001-0.01% B, balance Al and impurities.
Commercial automotive drawn 6061 tubing for driveshaft assemblies having yokes welded thereto is produced in T8 and T6 tempers. The T6 temper is produced using a furnace solution heat treatment after cold drawing to finish dimensions. Such solution heat treatments are conducted close to the melting point of the aluminum alloy and thus necessitate use of sophisticated equipment and process control, making the T6 process relatively expensive to carry out. The T8 temper is produced by solutionizing as part of the extrusion process, followed by drawing to finish dimensions. However, when the 6061 alloy is extruded into seamless tubing, grain size variation may occur from surface to center of the tube wall and there may be grain size variation along the length of the tube. Such variation can cause wrinkling during end reduction (a process used to adapt the tube ends to their associated yokes) and excessive total indicated runout (“TIR”) on reduced end tubes.
There is a need in the art for an economical process which produces light weight extruded aluminum tubes which can be used in driveshaft assemblies. It would be desirable for the aluminum alloy to exhibit a uniform fine grained structure which allows such extruded tube to be drawn without the need for an expensive separate furnace heat treatment. It would also be desirable if the alloy composition would allow the load requirements for extrusion to be reduced and thus increase the extrusion press productivity. Moreover, it would be desirable if such objectives could be met while also providing increased strength in the heat affected zone adjacent to the weld in the driveshaft assemblies while maintaining sufficient mechanical strength and torsional fatigue resistance.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the invention, an aluminum alloy containing 0.50 to 0.70% Si, up to 0.30% Fe, 0.20 to 0.40% Cu, up to 0.03% Mn, 0.80 to 1.10% Mg, up to 0.03% Cr, balance Al and impurities, can be used in an economical process to make a tube of a driveshaft assembly. A more preferred Si content is 0.55 to 0.65 % and a more preferred Mg content is 0.85 to 1.0%. The alloy may also include up to 0.20% Zn, preferably up to 0.05% Zn and/or up to 0.05% Ti. In order to obtain improved mechanical properties and elongation, the alloy preferably does not include any intentionally added elements which retard recrystallization during solid phase transformations. An especially preferred alloy consists essentially of at least 96% Al, 0.55 to 0.65% Si, up to 0.30% Fe, 0.20 to 0.30% Cu, up to 0.03% Mn, 0.85 to 1.0% Mg, up to 0.03% Cr, up to 0.05% Zn, up to 0.03% Ti.
In the case where the alloy comprises a tube of a driveshaft assembly, the tube can include a yoke welded to each end thereof. The tube preferably comprises a drawn and precipitation hardened extruded tube. The alloy can be processed in a T8 temper having a yield strength of at least 40 ksi, an ultimate tensile strength of at least 45 ksi, and an elongation of at least 5%. By appropriate choice of alloying constituents and/or processing, the alloy can be provided in a T8 temper having a yield strength of at least 45 ksi, an ultimate tensile strength of at least 50 ksi and an elongation of at least 10%.
The invention also provides a process of manufacturing an extruded tube of the aluminum-based alloy described above, the process comprising steps of extruding a billet of the alloy into an extruded tube, quenching the extruded tube from a solutionizing temperature to a temperature below about 200° F., and forming a drawn tube by drawing the extruded tube so as to reduce an outside diameter and wall thickness thereof. The extruded tube can be formed by any suitable technique such as piercing a solid billet of the alloy. The process can further include subjecting the drawn tube to a precipitation hardening heat treatment. The quenching step can be carried out by water cooling the extruded tube at a location adjacent an exit of an extruder used to extrude the tube. The drawn tube can be straightened by any suitable technique such as roller straightening. The drawn tube is preferably subjected to an aging treatment so as to impart a T8 temper to the drawn tube.
In the case where the extrusion is carried out such that the temperature of the extruded tube as it exits the extruder is around 950 to 1050° F., the water spraying preferably reduces the temperature of the tube to below about 150° F. In order to increase mechanical properties and elongation, the extruded tube is preferably subjected to natural aging for a suitable period of time such as one or more days (e.g., at least 4 days) subsequent to the extruding step and prior to the drawing step. The drawing step can be carried out in one or more passes to achieve a total reduction in area of 30 to 70%. For example, the extruded tube can be subjected to first and second drawing operations, each of which achieves a reduction in area of 15 to 35%. The quenching can be carried out by any suitable manner such as by spraying water circumferentially around the extruded tube. In the case where the extrusion is carried out such that the temperature of the extruded tube as it exits the extruder is around 950 to 1050° F., the water spraying preferably reduces the temperature of the tube to below about 150° F. In order to make driveshaft assemblies, the drawn tube can be sectioned (e.g., by sawing) into tube sections and welding yokes of a driveshaft assembly to opposite ends of each tube section. Depending on the design of the driveshaft assembly, it may be desirable to subject one or both ends of the tube to an end reducing operation to achieve a desirable outer diamet

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