摘要
The effect of transition elements on grain refinement of 7475 aluminum alloy sheets produced by warm rolling was investigated. The alloy which contains zirconium instead of chromium showed ultra fine structures with stable subgrains after warm rolling at 350 ℃, followed by solution heat treatment at 480 ℃. The average subgrain diameter was approximately 3 pan. It became clear that zirconium in solution has the effect of stabilizing subgrains due to precipitation of fine Al3Zr compounds during warm rolling. On the other hand, chromium-bearing compounds precipitate before warm rolling and they grow up to relatively large size during warm rolling. The warm rolled sheets with fine subgrains have unique properties compared with conventional 7475 aluminum alloy sheets produced by cold rolling. The warm roiled sheets solution heat treated had subgrain structures through the thickness with a high proportion of low-angle boundary less than 15°. The strength of the warm rolled sheets in T6 condition was about 10% higher than that of conventional 7475 aluminum alloy sheets. As the most remarkable point in the warm rolled sheets, the high Lankford （r） value of 3.5 was measured in the orientation of 45° to rolling direction, with the average r-value of 2.2. The high r-value would be derived from well developed r-fiber textures, especially with the strong {011 }（211） brass component. The warm rolled sheets also had high resistance to SCC. From Kikuchi lines analysis and TEM images, it was found that PFZs were hardly formed along the low- angle boundaries of the warm rolled sheets in T6 condition. This would be a factor to lead to the improvement of resistance to SCC because of reducing the difference in electrochemical property between the grain boundary area and the grain interior.
研究了温轧下过渡元素对7475铝合金板材晶粒细化的影响。经350°C温轧、480°C固溶热处理后,用Zr代替Cr的7475铝合金具有稳定亚晶超细组织;平均亚晶直径接近3μm。结果表明,溶液中的Zr能稳定亚晶是因为温轧中析出了细小的Al3Zr粒子;另一方面,含Cr粒子化合物在温轧之前析出,并且在温轧过程中会变粗大。与传统冷轧7475铝合金板材相比,温轧细化亚晶板材具有独特的性能。固溶处理后的温轧板材,在厚度截面的亚晶组织具有高比例小于15°的小角度晶界;温轧T6态合金板材的强度高于传统7475铝合金板材强度10%。温轧铝合金板材最显著的特点是,在与轧制方向呈45°时高Lankford(r)值为3.5,而其平均Lankford(r)值为2.2。高Lankford(r)值有利于组织演变为β-fiber织构,特别是强{011}?211?黄铜部分。同时,温轧板材也具有高的抗应力腐蚀开裂性能(SCC)。根据Kikuchi线和透射电镜分析,温轧T6板材形成的小角度晶界导致无沉淀析出带(PFZs)难以形成,这是导致抗应力腐蚀开裂性能提高的重要因素,其原因是晶界和晶内的电化学性能存在差异。
