The tensile deformation behavior of AA 3004 aluminum alloy
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AA 3004 aluminum alloy for can body stock exhibits interesting serrated flow in the stress-strain curves at room temperature. The serrated-flow phenomena are associated with dynamic strain aging and yield a negative strain-rate dependence of the flow stress. The occurrence of the serrated flow resulting from a negative dependence of the flow stress is well known to limit the formability of many alloys. In order to obtain an in-depth understanding of the serrated flow of the alloy, the characteristics of the serrations were examined as well as the dependence of flow stress on the strain rate and deformation temperature. A description of the effect of deformation temperature and strain-rate sensitivity on the mechanical behavior is discussed.
I.
INTRODUCTION
W I T H I N a certain regime of temperature and strain rate, serrations in the flow stress occur during deformation of alloys containing interstitial or substitutional solutes. The development of these serrations is generally referred to as the Portevin-Le Chatelier (PL) effect. The phenomenon of the PL effect is common to various alloy systems, l~-~2~The occurrence of the effect is ascribed to dynamic interactions between diffusing solute atoms and mobile dislocations. It is now well established that the serrated flow associated with dynamic strain aging results in a negative strain-rate dependence of the flow stress. Thus, negative strain-rate sensitivity is a common feature in a variety of materials, provided test conditions are chosen such that serrated yielding occurs. The phenomenon of negative strain-rate sensitivity results in limiting formability, an increase in the inhomogeneity of deformation, and irregular surface markings. I~3.~4j Many aluminum alloys are known to be particularly susceptible to negative strain-rate sensitivity, t~5-zz] AA 3004 aluminum alloy is of considerable economic importance in making two-piece beverage cans. In 1990, approximately 90 billion 12-ounce aluminum two-piece cans were produced in the United StatesJ 23] These aluminum cans use a body stock made of AA 3004-H19, and the present intention is to reduce the thickness of the body-stock gage to 0.25 m m from 0.32 mm. This remarkable decrease in gage demands higher-strength alloys with adequate forming performance. Therefore, a better understanding of the mechanical behavior of the A1-Mn-Mg alloys is imperative for the improvement of alloy strength and formability. Most of the investigations to date, however, have concentrated on the effect of thermomechanical treatment on microstructure and earing behavior. Little attention has been paid to the serrated flow in the stress-strain curves of AA 3004 aluminum alloy. Therefore, this research was undertaken to examine the characteristics of serrated flow in AA 3004 aluminum alloy in terms of the plastic onset D. PARK, G r a d u a t e S t u d e n t , D e p a r t m e n t of M a t e r i a l s Engineering, and Research Assistant, Light Metals Research Labs, and J.G. MORRIS, Professor of Metallurgical Engineering, and Director, Ligh
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