Abstract
By changing the temperature and time of two step aging, three aging conditions of 7050 aluminum alloy, namely: under aging, peak aging and over aging were obtained. After aging, some of the materials were cold rolled to a reduction in thickness of 20%. The plane strain compression test in S direction to different amount of reduction in thickness in a channel die with T or L direction constrained was performed at room temperature. The formation of shear bands and the true stress -true strain curves were studied. In plane strain compressed specimens with either T or L direction constrained, macroscopic shear bands were visible on the constrained plane surface of the specimen. The shear bands formed along planes of maximum shear stress which make an angle 45 degree to the S and the non-constrained plane. The shear bands are more clear when T plane is the constrained plane. The maximum shear strain observed in a shear band is 2. It was noticed that the strength of specimens constrained in L direction were higher than that of their counterpart specimens constrained in T direction. For under aged specimen, the shear bands was sharply localized. Specimen will shear rupture along shear bands with a sudden drop of the stress. Similar but wider shear bands were observed in peak and over aged specimens. The width of over aged specimens was the largest. No rupture were observed in over aged specimens even when the true compression strain went up to 0.6 when the test ended. For under aged specimen with T direction constrained, the true strain of rupture is 0.32. For cold rolled specimen, the formation of shear bands occured at a smaller strain and the true strain of rupture is 0.27. When constrained in L direction, the rupture strain, 0.29 for underaged and 0.125 for underaged and cold rolled specimens was smaller than those in T direction. In contrast to the underaged case, for over aged specimens the stain of shear band formation was larger when constrained in L direction than in T direction. A model based on the dislocation- precipitate interaction was proposed to explain these observations. The effect of precipitates upon the formation of shear bands observed in the study was mainly macroscopic slip. No matter the plane strain compression by T direction constrained or L direction constrained, the angles between the macroscopic shear bands and compress plane are all about 45° which is the same with maximum shear plane. It is suggested that the effect upon the formation of shear bands were mainly subjected to the precipitates and maximum shear plane, and slight for the orientation in the individual grain or the texture.