7174 sale of imported aluminum tubes / high-precision aluminum tube aluminum Al: margin; silicon Si: 0.25; copper Cu: 0.10; Mg Mg: 2.2 ~ 2.8; Zinc Zn: 0.10; Mn Mn: 0.10; chromium Cr: 0.15 ~ 0.35; iron Fe: 0.4 0. Tensile strength (σb): 170 ~ 305MPa Conditions yield strength σ0.2 (MPa) ≥65 modulus of elasticity (E): 69.3 ~ 70.7Gpa annealing temperature: 345 ℃. Aluminum is the industry's most widely used non-ferrous structural materials, have been widely used in aviation, aerospace, automotive, machinery, shipbuilding and chemical industries. With the rapid development of science and technology and industrial economy, the demand for aluminum alloy welded structure is increasing, so that the welding of aluminum along with in-depth research. Aluminum is widely used to promote the development of aluminum welding technology, welding technology development and also expand the applications of aluminum, aluminum welding technology is becoming one of the hot research. Aluminum elements are most abundant in the earth's crust metallic element content higher than 7%. Al atomic number 13, atomic weight of 26.98, atomic volume (cc / mol): 10.0, face-centered cubic structure, melting point 660 ℃, the density of 2.702, the crust content (ppm): 82000. Heat treatment of aluminum alloy castings is the choice of a heat treatment specifications, control the heating rate rise at a certain temperature for a certain time and corresponding to a certain speed of the cooling was changing its organizational alloy, and its main purpose is to improve the mechanical properties of the alloy, and enhance resistance corrosion, improve the processing type can obtain dimensional stability. Features aluminum heat treatment is well known for high carbon steels, after quenching to obtain high hardness immediately, while the plastic is very low. Aging at different temperatures, precipitation of different critical nucleus size, quantity, composition, and gathered speed phase of growing up, if the temperature is too low, due to the proliferation of difficulty, G · P area difficult to form, after aging strength, low hardness, when the effect When the temperature is too high, the proliferation of easy to make, big supersaturated solid solution of the critical nucleus size precipitates after aging strength, low hardness, which produce over-aging. Thus, various alloys have optimum aging temperature. Aluminum regression phenomenon through natural aging after quenching aluminum (such as aluminum - copper) reheated to 200 ~ 250 ℃, and then quickly cooled to room temperature, the alloy strength decreases, re-softened, performance back to just quenched state; if left at room temperature, then quenched with new alloys, as still normal natural aging, a phenomenon known as regression phenomenon. Explanation of regression phenomenon is naturally aging the alloy at room temperature, the formation of G · P zone size is small, when heated to a higher temperature, these small G · P zone is no longer stable and re-dissolved in solid solution, The Alloy rapid cooling to room temperature, then quenched alloy has returned to a new state, you can still re-natural aging. In theory, limit the number of regression is not treated, but in fact, it is difficult to deal with when you return precipitates completely reconstituted, was caused by the aging process after partial precipitation, so that the effect of successive aging strengthening weakened. While in the course of repeated heating, solid solution crystal grains there is a growing trend, this performance disadvantage. Therefore, regression is used only for repair aircraft alloy rivets, you can take advantage of this phenomenon, at any time riveting, while aluminum is no other value.