Mechanical Properties and High Temperature Deformation Behavior of Al -Cu- Mg Alloys Microalloyed

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One of the prime research objectives in the area of structural materials for aircraft and space applications is to develop light weight alloys exhibiting high strength, reasonable ductility, high fracture toughness and good corrosion resistance properties. In this respect, Al alloys, especially the precipitation strengthened wrought 2xxx, 6xxx and 7xxx series of alloys have been investigated extensively. Though the mechanisms of strengthening and toughening of these age hardenable alloys are now fairly well understood, there exists a great demand for the development of alloys exhibiting still higher strength to weight ratio. Microalloying alloys with elements such as Sn, In, Cd, Ag, Si, etc. is one of the strategies being explored to achieve this goal. While the influence of alloying elements on the structure and properties of commercial aluminum alloys is well documented, detailed investigations on the effect of trace additions of elements like Sn, In, Cd, Ag, in heat treatable 2xxx series of aluminum alloys are still very few. The effect of systematic variation of trace amounts of Sn on the microstructure, mechanical properties and high temperature deformation behavior of these wrought Al alloys has not yet been explored. Processing of these microalloyed wrought alloys by a sequence of casting, intermediate heat-treatments, hot deformation and final heat treatment would lead to the development of alloys with required microstructure and mechanical properties suitable for structural applications. The general lack of information in the literature in the above area gives rise to several issues worth investigating. The present thesis work was undertaken with the following objectives: - To process Al-5.9%Cu-0.5%Mg (by weight) alloys microalloyed with Sn of varying D To study the precipitation kinetics, evaluate the kinetic parameters and thereby generate the kinetic rate equation for the investigated alloys. D To study the effect of Sn addition on the high temperature deformation behavior of the investigated alloy system. D To generate constitutive equation for modeling the high temperature flow characteristics and predicting peak flow stress of the alloys with varying Sn contents and at different deformation conditions. D To generate a model and thereby predict the flow stress as a function of strain, strain rate and temperature of all the investigated alloys at different deformation conditions by Artificial Neural Network and Multiple Linear Regressions analysis techniques. D To generate processing maps for the investigated alloy system. Six different alloys with varying Sn contents were prepared by casting route. Optical and scanning electron microscope studies revealed dendritic structures for the alloys in the as-cast condition. Two types of second phases were observed at the grain boundary regions of the alloy matrix, both in as-cast as well as in cast and homogenized conditions. One of the second phases (AlDCuDSiDFeDMn phase) existed with script morphology. The other phase was identified as CuAl2 (q-phase). The grain size of the ascast alloys was not influenced by Sn content. But the hardness of the alloys was dependent on the Sn content in the alloy. The maximum hardness of both as-cast and solutionized alloys could be observed in the alloy with 0.06 wt.% of Sn. For the cast and homogenized alloys, the yield strength and ulti...
Supervisor: P.S. Robi and A. Srinivasan