Metal fusion bonding – Process – Using dynamic frictional energy
Utility Patent
1998-06-23
2001-01-02
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Using dynamic frictional energy
C228S114000, C148S415000, C148S535000, C148S690000
Utility Patent
active
06168067
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to high strength friction stir welding. More particularly, the present invention relates to reducing material property degradation during friction stir welding of precipitation hardened parent materials.
BACKGROUND OF THE INVENTION
Friction stir welding is utilized to join workpieces to form structural assemblies that can be used in the manufacture of military and commercial aircraft. As illustrated in
FIG. 1
, friction stir welding involves inserting a rotating friction stir welding probe
10
between the opposing faces of a pair of workpieces
12
,
14
while urging the workpieces together. The rotation of the friction stir welding probe between the opposing faces of the workpieces creates friction that generates sufficient heat energy to plasticize the workpiece material in the weld zone
16
. A weld joint
18
forms, joining the workpieces together in a unitary assembly, as the plasticized regions of the workpieces flow together and solidify in the weld zone. Alternatively, a plasticized region between the workpieces can be formed without utilizing a friction stir welding tool by moving one of the workpieces relative to the other while concurrently urging the workpieces together.
One particular benefit of friction stir welding is that the formation of the weld joint
18
is autogenous and is created by the solidification of the plasticized parent materials rather than a filler material, as is commonly used in conventional welding processes. However, the frictional heat necessary to plasticize the workpiece material during friction stir welding can degrade the mechanical properties of the parent materials. As shown in
FIG. 1
, during friction stir welding, the frictional heat created by the rotating friction stir welding probe
10
is conducted from the weld zone
16
through the workpieces
12
,
14
into the ambient environment, creating a heat-affected region
20
around the weld zone. The elevated temperatures associated with the friction stir welding process can degrade the mechanical properties of the parent materials, including the strength, stiffness, and ductility, in both the weld zone and the heat-affected region.
Material property degradation is particularly problematic when friction stir welding precipitation hardened parent materials, which have improved mechanical properties obtained through expensive solution and precipitation heat treatment processes. When friction stir welding precipitation hardened workpieces, the joined workpieces commonly require an additional quenching cycle, including heat treating the workpieces at a predetermined temperature schedule and then rapidly cooling the workpieces. The quenching process must then be followed by either natural or artificial aging at a second predetermined temperature schedule to recover the parent material properties. Quenching operations are not only costly, but can warp the welded assembly resulting in poor dimensional quality and requiring additional straightening processes that further increase the cost of manufacture.
Thus, there is a need for improved methods of friction stir welding heat treated materials, and particularly precipitation hardened materials. Such manufacturing methods should be cost effective, as well as minimizing the degradation of the material properties obtained through precipitation hardening.
SUMMARY OF THE INVENTION
The present invention provides a method for reducing the material property degradation during friction stir welding by friction stir welding materials in a nonequilibrium state and having a correspondingly incomplete temper. According to the present invention, the first and second structural members are solution heat treated at a first predetermined temperature schedule. Next, the first and second structural members are quenched to a predetermined temperature at which the structural members have an incomplete temper and are in a nonequilibrium state. The first structural member is then positioned adjacent to the second structural members, thereby defining an interface therebetween. Thereafter, the first and second structural members are joined to form a structural assembly by friction stir welding the material along the interface prior to precipitation heat treating the structural assembly.
In particular, the structural assembly formed by joining the first and second structural members is preferably precipitation hardened by aging the structural assembly at a second predetermined temperature schedule which stabilizes the material properties and completes the temper of the resulting structural assembly and creates a structural assembly. The structural assembly is then cooled to ambient temperature. The structural assembly can then be secured to other structural assemblies so as to form the frame of an aircraft.
Simultaneously with the joining step, the first and second structural members are further quenched to reduce the size of the heat-affected region in the first and second structural members. In one embodiment, the quenching step includes applying a liquid coolant to the first and second structural members using at least one liquid coolant jet. In another embodiment, the quenching step includes applying a gaseous coolant to the first and second structural members using at least one gaseous coolant jet. In another embodiment, the quenching step includes applying a liquid coolant to the first and second structural members by submersing the first and second structural members in a liquid coolant bath.
Therefore, the present invention provides a method for forming a precipitation hardened structural assembly which overcomes the shortcomings of conventional techniques. The method requires fewer manufacturing steps than conventional techniques for friction stir weld precipitation-hardened parent materials. In addition, the method minimizes the degradation of the material properties during friction stir welding, and produces a structural assembly with improved strength and hardness, as well as dimensional quality.
REFERENCES:
patent: 2744039 (1956-05-01), Siegel
patent: 3234643 (1966-02-01), Hollander
patent: 3554513 (1971-01-01), Chance
patent: 3629546 (1971-12-01), Fry
patent: 3773260 (1973-11-01), Kunioka et al.
patent: 3948428 (1976-04-01), Bonomo et al.
patent: 4223197 (1980-09-01), Imai et al.
patent: 4236920 (1980-12-01), Lampe et al.
patent: 4426429 (1984-01-01), Di Russo et al.
patent: 4589932 (1986-05-01), Park
patent: 4811888 (1989-03-01), Ziemek et al.
patent: 4857694 (1989-08-01), Doyle et al.
patent: 4897124 (1990-01-01), Matsuo et al.
patent: 5014901 (1991-05-01), Moran
patent: 5077081 (1991-12-01), Bedford
patent: 5122339 (1992-06-01), Pickens et al.
patent: 5211910 (1993-05-01), Pickens et al.
patent: 5259897 (1993-11-01), Pickens et al.
patent: 5375758 (1994-12-01), Roberts, Sr.
patent: 5455003 (1995-10-01), Pickens et al.
patent: 5460317 (1995-10-01), Thomas et al.
patent: 5462712 (1995-10-01), Langan et al.
patent: 5507888 (1996-04-01), Dickson, Jr. et al.
patent: 5611479 (1997-03-01), Rosen
patent: 5794835 (1998-08-01), Colligan et al.
patent: 5837070 (1998-11-01), Sainfort et al.
patent: 5951794 (1999-09-01), Dickson, Jr.
patent: 356133414 (1981-10-01), None
patent: 357207117 (1982-12-01), None
patent: 359136451 (1984-08-01), None
patent: 362192567 (1987-08-01), None
patent: 403271352 (1991-12-01), None
patent: 10286682 (1998-10-01), None
patent: 1000199 (1983-02-01), None
patent: WO 99/39861 (1999-08-01), None
Pettit Richard G.
Waldron Douglas J.
Alston & Bird LLP
McDonnell Douglas Corporation
Ryan Patrick
Stoner Kiley
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