Abstract: A backing member for a friction stir butt welding apparatus includes a groove in the working surface of the backing member which supports the workpieces being butt welded. The backing member is positioned with the groove aligned directly beneath the butt joint between the workpieces. A rotating friction stir welding pin is introduced at the joint so as to plasticize the material of the workpieces on either side of the joint, and pressure is applied between the stir pin and the workpieces to create a forging pressure which forces plasticized material downward through the root zone of the weld and into the groove in the backing member. A visible bead is thus produced on the lower surfaces of the workpieces indicating total penetration of the weld. Lack of a bead indicates probable failure of the weld to totally penetrate through the root zone.

Abstract: The present invention provides an improved structural assembly constructed of a plurality of structural members secured together. At least one of the plurality of structural members defines a first region characterized by comparatively high operational stress and a second region having a locally refined grain structure positioned such that the second region at least partially encompasses the first region to thereby enhance the strength, toughness and fatigue resistance of the at least one structural member in the first region. The present invention also provides a method for selectively improving the strength, toughness and fatigue resistance of a structural member in a region of high operational stress including the steps of casting the structural member in a pre-selected configuration. Regions of the structural member having comparatively high operational stress are identified. The structural member is secured to prevent movement.

Abstract: A friction stir welding apparatus includes a C-shaped frame having two opposing jaws which are spaced apart to define a space for receiving workpieces which are to be welded together. One of the jaws supports a rotatably driven friction stir welding spindle, and the other jaw supports a back-up tool. The spindle is supported in a polycrystalline thrust bearing disposed in the one jaw for absorbing thrust forces exerted on the spindle during a welding operation. The C-shaped frame may be an integral one-piece structure, in which case the apparatus and workpieces are relatively advanced to cause the spindle to penetrate the workpieces at an edge thereof and to carry the welding tools along a weld path to a second edge of the workpieces, where the spindle exits and disengages the workpieces.

Abstract: A process for joining two or more overlapping metal workpieces includes providing a fastener which is made of metal having a melting point temperature at least as great as that of the workpieces. The fastener is rotated about its central axis and is axially advanced at a predetermined advance rate into engagement with the workpieces so as to cause plasticization of the workpieces at the interface with the fastener, and to cause the fastener to axially penetrate through substantially the entire thickness of the workpieces. The rotation of the fastener is then stopped, and the plastic zone which surrounds the fastener cools to form a metallurgical bond with the fastener. The resulting fastened joint is mechanically superior to conventional mechanically fastened joints made by rivets and the like.

Abstract: A method for reducing material property degradation during friction stir welding. More specifically, the method includes the steps of solution heat treating first and second structural members at a first predetermined temperature schedule. The first and second structural members are then quenched to a predetermined temperature at which the structural members are in a nonequilibrium state and have an incomplete temper. The first structural member is then positioned adjacent to the second structural member, 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. The structural assembly is then aged, such as by precipitation heat treating, at a second predetermined temperature schedule to stabilize the material properties of the resulting structural assembly, thereby completing the temper of the material.

Abstract: A dual aging treatment of aluminum-copper-lithium-scandium alloys allows preparation of alloys exhibiting superior physical properties as compared to the same alloys subjected to only a single aging. In particular, the difference between yield strength and ultimate tensile strength is markedly increased. The alloys are characterized by an array of fine T1 phase precipitates within the aluminum grain, leaving a substantially T1 phase precipitate-free zone along the grain boundaries, and an array of coarse .theta.' and .delta.' phase precipitates throughout the grains with little or no .theta.' and .delta.' phase-free zones.

Abstract: Aluminum/lithium alloys displaying excellent weldability while also exhibiting isotropic physical properties is produced by including greater than 0.25 weight percent scandium and processing by a combination of low temperature hot working, recrystallization, optional cold working, and artificial aging. The alloy materials are particularly useful as aircraft and spacecraft components such as fuel tanks.

Abstract: A plasma arc welding torch wherein a first plasma gas is directed through the body of the welding torch and out of the body across the tip of a welding electrode disposed at the forward end of the body. A second plasma gas is disposed for flow through a longitudinal bore in the electrode. The second plasm gas enters one end of the electrode and exits the electrode at the tip thereof for coacting with the electric welding arc to produce the desired weld. A shield gas is directed through the torch body for circulating around the head of the torch adjacent the electrode tip.