Evolution of texture and microstructure in a thermomechanically processed Al-Li-Cu-Mg alloy
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I.
INTRODUCTION
THE Al-Li alloys, because of their low density and high modulus, are becoming attractive for applications in the aerospace industries.[1,2,3] A desired characteristic of these materials for such applications is uniformity of mechanical properties in all directions. In practice, however, these materials are prone to develop marked anisotropy of mechanical properties after processing.[4] This has been attributed to either the preferred orientation of grains, i.e., texture,[5] or to morphological features such as precipitates (notably d),[6] elongated grain boundaries, and incomplete recrystallization.[7] Among these, texture appears to play the dominant role in yield strength anisotropy,[5] while the remaining factors influence anisotropy of toughness and fatigue properties.[7] The evolution of texture in Al-Li alloys has been studied by several workers.[8,9,10] Vasudevan et al.[8] investigated the effect of composition on the development of texture in hotrolled binary Al-Li alloys. They observed primary Goss and secondary Cube components at low Li levels and well-developed b fibre in alloys with high Li content. Engler et al.[9] have studied the specific roles of Li, Zr, and Cu in AlLi base alloys in influencing texture evolution during hot rolling. It was reported that hot rolling of Zr containing alloys led to a strong Bs texture component, while CR of all the alloys resulted in the usual Talyor type b fibre components. Texture evolution in a 8090 Al-Li alloy was exA.K. SINGH, G.G. SAHA, and A.A. GOKHALE, Scientists, are with the Defence Metallurgical Research Laboratory, Hyderabad—500058, India. R.K. RAY, Professor, is with the Department of Materials and Metallurgical Engineering, Indian Institute of Technology, Kanpur— 208016, India. Manuscript submitted May 9, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
tensively studied by Bull and Lloyd[10] as a function of hot rolling and CR, hot cross rolling, and postrolling solution treatments. The aforementioned studies on texture evolution in AlLi alloys were not supported by detailed microstructural observations. The textural information, in most cases, was presented in the form of pole figures and was therefore only qualitative in nature. In the present work, the evolution of texture in a quaternary Al-Li-Cu-Mg alloy (similar to 8090) has been studied, in conjunction with extensive microstructural characterization, in hot-rolled, cold-rolled, and heattreated conditions. The textures were measured using both the pole figure and the orientation distribution function (ODF) methods. The processing here consisted of hot cross rolling followed by straight CR, ST (and further CR, etc.), which was quite different from the schedule used by Bull and Lloyd.[10] The aim of the present work was to evaluate the effect of the processing schedule on microstructural and textural development with special reference to the possible reduction of the texture severity in this alloy. Finally, the results obtained in the present work were compared with those of Bull a
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