Effect of Composition and Distribution of Phases after Aging on Stamp Ability for Aluminum Alloy D16 (AA2014) Sheets
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The relevance of this research is connected to the increasing requirements for accuracy in stamped parts produced from aged aluminum alloys, and can also be applied for making layered composites. Indexed requirements can be provided by controlling the structure of sheet blanks, particularly by the phase composition and distribution behavior. Results of experimental research into the effect of aging modes on composition, dispersion behavior, and stamping number of sheet samples of the D16 aluminum alloy (AA2014) are presented. Heat treatment includes quenching from a temperature of 500°С into water of room temperature and further aging: natural aging for 7 days and artificial aging at temperatures of 50, 100, 150, and 200°С with a duration at each temperature of 15, 30, 60, 120, and 240 min. A method of estimating the quantity of the characteristics of dispersion phases is proposed for the microstructural picture. Stamp ability is evaluated using the stamping number, which is the ration between yield stress and tensile strength. It is found that increasing aging temperature and durance leads to the growth of the stamping number, which shows a low ability for sheet-stamping operations of alloy. Aging at 50°С did not lead to the sedimentation of dispersion phases for either optical metallography or scan electron microscopy. The inhomogeneity of phase dispersion inside the grain grows at the initial stages of aging, when durance is less than 1 h and temperature is 100, 150 and 200°С. Further increasing durance to 4 h leads to inhomogeneity decreasing. There is no correlation between the uniformity of phase dispersion and the stamping number. The chemical composition of phases plays the main role in stamping number, outside of phase-dispersion uniformity. The phase-composition changes depend on the mode of heat treatment: at an annealed and naturally aged state, the θ and S phase is sediment. After aging at a temperature lower 150°С after a short durance of less than 1 h, the θ, S and T phases are revealed; the θ phase appears after aging at temperatures higher than 150°C and long durance reaching 4 h.
Keywordsaluminum alloy structure stamping number aging phase composition phase dispersion
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