Hot Compression Temperature And Quench Sensitivity Of 7050 Aluminum Alloy Microstructure

Aluminum alloy7050has been widely used in aerospace industry due to its high properties of strength and toughness. However,7050alloy has poor plasticity at room temperature with high alloyed elements, so its large plastic deformation is usually realized under high temperature condition. Not only the shape and size, but also the microstructure will change greatly during hot deformation. The genetic characteristics of the microstructures will have important influence on the subsequent heat treatment and its final performance. Multi-pass plane-strain hot compression of7050aluminum alloy was carried out on Gleeble-1500thermal simulator in order to simulate its cooling behavior during rolling. The microstructure was analyzed by means of optical microscopy, scanning electron microscopy and transmission electron microscopy while the properties were investigated by means of hardness testing, electrical conductivity. The microstructure evolution, deformation behavior and the effects of finishing hot-compression temperature on quenching sensitivity were investigated. The main conclusions are as follows:(1) The effects of finishing hot-compression temperature on deformation behavior of7050aluminum alloy were determined. The flow stress increased gradually with the increasing pass number when the finishing hot-compression temperature was300℃. With increasing temperature, the flow stress of the same pass decreased gradually. The flow stress decreased gradually with increasing pass number at finishing hot-compression temperature of430℃.(2) The effects of finishing hot-compression temperature on the second phase in7050aluminum alloy were obtained. With increasing pass number, the coarse residual phases were broken into fine particles showing linear distribution. The number of coarse phases decreased gradually with the increasing finishing hot-compression temperature, after both hot deformation and solution treatment. The increasing temperature of hot deformation was helpful to improve the effect of solution. With decreasing temperature, the number of MgZn2which precipitated from matrix increased gradually.(3) The effects of finishing hot-compression temperature on recrystallization during solution treatment. When finishing temperature of hot-compression was300℃, there was a large number of minimize sub-grains and high density of dislocation in the microstructure after hot-deformation with high stored energy. The stored energy decreased gradually with the increasing finishing temperature. While the size of sub-grains increased and the density of dislocation decreased gradually. So the recrystallized microstructure in the sample after solution treatment decreased gradually with increasing finishing temperature.(4) The effects of finishing hot-compression temperature on quenching sensitivity of7050aluminum alloy were obtained. Plenty of equilibrium phases η precipitated on Al3Zr during the air-cooling after solution treatment, which consumed massive Zn、Mg alloying elements and reduced the superstauration of the alloy. The strengthening phase η precipitated from matrix with lower driving force during aging process. The performance loss of the alloy decreased gradually with the reducing recrystallized microstructure in the sample. The quenching sensitivity decreased gradually with the increasing temperature of hot-deformation.