外 文 翻 译毕业设计题目： 双搅拌轴搅拌摩擦焊机设计 原文1： AN OUTSIDER LOOKS AT FRICTION STIR WELDING 译文1： 常人眼中的摩擦搅拌焊接技术 (原文1) AN OUTSIDER LOOKS AT FRICTION STIR WELDING BACKGROUND4.1 Solid State Welding, Overview 2-4 FSW, the subject matter of this document, is the newest addition to friction welding (FRW), a solid state welding process. Solid state welding, as the term implies, is the formation of joints in the solid state, without fusion. Solid state welding includes processes such as cold welding, explosion welding, ultrasonic welding, roll welding, forge welding, coextrusion welding and FRW. Conventional FRW in its simplest form involves two axially aligned parts, one rotating and the other stationary. The stationary part is advanced to make contact with the other, at which point an axial force is applied and maintained to generate the frictional heat required to affect welding at the abutting surfaces and form a solid-state joint. The joint is achieved by upset forging at the elevated temperatures generated by friction. There are two FRW techniques. The first is direct / continuos drive FRW, where constant energy is provided by a source for the desired duration. The second is inertia drive FRW, where a rotating flywheel provides the required energy. A variant of the conventional techniques, radial friction welding, is used for hollow sections, such as tube and pipe. Here, a solid ring is rotated and compressed around the abutting beveled ends of the stationary pipes / tubes to be welded. A support mandrel is located at the bore, at the welding position, to prevent the collapse of the pipe / tube ends. Another variant is friction surfacing, where metal layers are deposited on a substrate. Here, a rotary consumable is brought into contact with a moving substrate to affect metal transfer from the consumable to the substrate. 4.2 Friction Stir (FS) Technology 5, 6 FSW is a member of the FS technology family. The other members of that family are FS processing for superplasticity, FS casting modification (also referred to as FTMP or friction thermomechanical processing), FS microforming, FS powder processing, FS channeling and FS processing for low temperature formability. 4.3 A Note on Aluminum Alloys Since the majority of work reviewed in this document pertains to aluminum alloys, it is important to discuss some of the heat treatment aspects of these alloys. A three-step sequence is used to heat treat 2xxx, 6xxx and 7xxx series and other heat treatable aluminum alloys, to higher strength levels. The first step is solution heat treatment and it consists of heating to some prescribed elevated temperature (around 900 F) and soaking there for a prescribed period of time. The second step is to cool the alloy fast enough (e.g., by quenching), so as to retain the elevated temperature microstructure. As will become clear shortly, cold working, forming or straightening of quenched wrought alloys should be performed as soon as possible after quenching. The third step is aging (AKA precipitation heat treatment). Aging involves soaking the alloy for a period of time at some temperature that is lower than that used for solution treatment. For the aluminum alloys of concern here, aging is performed in the room temperature to 375 F temperature range. Aging at room temperature is referred to as natural aging. Aging at temperatures above room temperature is referred to as artificial aging. Aging causes precipitation within the grains, with the attendant increase in strength and hardness, at the expense ductility. Other properties also change as a result of aging. 4.3.1 Natural Aging After quenching, the alloy is in the unstable -AQ temper. At room temperature, the alloy remains in that temper for a period that ranges from a few minuets to an hour or so, depending on the particular alloy. During that period, the solution treated microstructure remains as it was at the solution treatment temperature; i.e., remains unchanged. At the end of that period, the temper changes to the -W temper, also an unstable temper. This isaccompanied by changes in properties; e.g., the strength and hardness will increase and the ductility will decrease. As more precipitation occurs with time, the properties will progressively evolve; e.g., strength will progressively increase and ductility will progressively decrease with time. After a few days (or about 96 hr), 2xxx and 6xxx alloys reach a stable condition, referred to as the -T4 temper where no further property changes would take place. An additional increment of strength can be obtained in 2xxx alloys if the alloy is cold worked in the -AQ temper or during the early stages of the -W temper, and then naturally aged, for about 96 hr, to a stable condition referred to as the -T3 temper.