The 7075 alloy is the most typical aviation super duralumin. It is not only an "ancient" AL-Zn-Mg-Cu alloy, but also a "vigorous" young alloy. It is said to be "ancient" because it is the first to be finalized The super duralumin, which was finalized in 1944, was used to manufacture aircraft in the United States, Japan, and the former Soviet Union. It is only 74 "years old" and is still in the "middle-aged" stage. It is called "young" because it is still The main material of the key structure of aerospace vehicles, it seems that only when composite materials can be mass-produced industrially and the price is reduced to be competitive with super-duralumin, super-duralumin will withdraw from the stage of history and give way to composite materials.
After more than 70 years of development, 7075 alloys have formed a rather large family. Now commonly used alloys include 7075/7175/7475 alloys. Due to unsatisfactory performance, 7275 alloys have become a very useful alloy, while 7375 alloys have been completely eliminated. Never use it again.
The 7175 alloy is cleaner than the 7075 alloy, and the 7475 alloy is cleaner, that is, their impurity content is lower than the other. For example, the silicon content of the 7475 alloy is only 25% of that of the 7075 alloy, which is 0.30 percentage points smaller than that of the 7075 alloy, so 7475 The alloy has higher toughness and better comprehensive performance.
7075 alloy is an aluminum-zinc-magnesium-copper series high-strength deformable aluminum alloy that can be strengthened by heat treatment. It is the veteran of super duralumin, but it is not a big brother, because there are still stronger ones, and it can be used to process all semi-finished products. , used to manufacture a variety of structural parts, especially aerospace structural parts, is the most widely used high-strength aluminum alloy today, as large as the C919 large aircraft front fuselage long stringer, passenger observation window frame forgings, medium aircraft Body bends and girders, keel beam webs, floor transition beams, middle and rear fuselage girders, passenger observation window frame forgings, cargo door frames, nose front pressure frame flanges, door frames, etc.; small to mobile phone casings. It has a variety of heat treatment states: T6, T73, T76, T77. T6 state materials have the highest mechanical strength properties, but the fracture toughness is low, sensitive to stress corrosion, and because the toughness decreases with the decrease of temperature, therefore, T6 state materials are not suitable for manufacturing low temperature structural parts and workpieces; T73 material strength It is the lowest, but has quite high fracture toughness, good stress cracking resistance and exfoliation corrosion resistance; the strength of T76 material is higher than that of T73 material, and its resistance to stress corrosion cracking is higher than that of T6 material. The static strength performance of the 7075 alloy is higher than that of the 2024 and 2124 alloys, and the fatigue performance is comparable to them. O-state and W-state materials have good room temperature formability.
7075 alloy can be resistance welded, and the long-term working temperature of the workpiece is ≤125°C. Incomplete annealing specification for materials or workpieces is 290°C~320°C, heat preservation for 2h~4h, and then air cooling out of the furnace; complete annealing specification (390~430)°C/(0.5~1.5)h, with a cooling rate not greater than 30°C/h Cool to ≤200°C, then air cool.
The solution treatment temperature of the
7075 alloy plate is 460°C~490°C, and the treatment temperature of the aluminum plate should be close to the lower limit, and the number of repeated treatments should not be more than 2 times, so as to prevent the alloy elements from diffusing through the aluminum clad layer and reducing the corrosion resistance of the material ; The heating temperature of extrusion material is 460℃~471℃. After heat preservation, quench in room temperature water or warm water or other suitable cooling medium, and the transfer time should be <15s.
