Hot Deformation Behavior Of The Al-Zn-Mg-Cu-Zr Alloys During Compression At Elevated Temperature

Al-Zn-Mg-Cu-Zr alloys have a combination of high strength and fracture toughness, as well as resistance to stress corrosion cracking that renders them very useful in the aircraft and aerospace industry applications. As China's aerospace, aviation, weapons and equipment, especially in space industry has been developed very rapidly in recent years, higher requirements for properties of materials are demanded. In this present, the hot deformation behaviors of two different Al-Zn-Mg-Cu-Zr aluminum alloys (7150 alloy and 7056 alloy) were studied by means of compression deformation tests on Gleeble 1500 machine at strain rates ranged between 0.01s^-110s^-1 and deformation temperature 300℃⁴50℃,and associated structural changes were studied by observations of metallographic and TEM. The results are shown as following:1. The true stress - true strain curves of 7150 and 7056 aluminum alloys both appear steady-state deformation features apparently. At low strain rate, the true stress increases with true strain rapidly and enters a steady state after reached peak flow. At high strain rate, the true stress decreases sharply after the peak, then the curves enter steady-state deformation stage.2. Maximum stress for 7150 and 7056 aluminum alloy both can be represented by a Zener-Hollomon parameter in the hyperbolic-sine-type equation with the hot deformation activation energy Q of 226.6988KJ/mol and 244.6442KJ/mol.3. The microstructure of 7150 and 7056 aluminum alloy after hot compression deformation transform from dynamic recovery to dynamic recrystallization as decreasing the value of parameter Z.4. The number and distribution of dislocation change with deformation condition. Decreasing of Z value, that is increasing deformation temperature or decreasing strain rate, leads to a large number of dislocations neutralize and the density of dislocation decrease. During compression process, the dynamic precipitation of precipitates increase as increasing of parameter Z, which results in the level of flow stress under low deformation temperature and high deformation rate much higher than under high deformation temperature and low deformation rate.5. The grain size of 7150 aluminum alloy after compression is less than which of 7056 aluminum alloy under the same conditions.The precipitations of 7150 alloy are much more that of 7056 alloy, but the precipitations size are finer than 7056 alloy.All of these maybe result in the flow stress level of 7150 alloy beyond 7056 alloy.