EFFECT OF DISPERSED PHASE COMPOSITION AND DISTRIBUTION AFTER AGING ON FORMABILITY OF D16 ALUMINIUM ALLOY SHEETS

The relevance of this paper is connected with rising accuracy requirements to stamped parts made of aged aluminium alloys applied also for layered composite making. These requirements can be met by controlling the sheet blank structure, and particularly its phase composition. The paper provides experimental results obtained when studying the effect of aging modes on the composition, dispersed phase distribution pattern and formability of sheet samples made of D16 (AA2024) aluminium alloy. Heat treatment consisted in quenching from a temperature of 500 °С into room temperature water and further aging: natural aging during 7 days, artificial aging at temperatures of 50, 100, 150 and 200 °С and holding at each temperature during 15, 30, 60, 120 and 240 minutes. The quantitative method is proposed to evaluate the dispersed phase distribution pattern by microstructure pictures. Formability was evaluated using the stamping number, i.e. a proof/ultimate factor. It was found that the stamping number rises as the aging temperature and holding time are increased, which shows the lower alloy applicability for sheet stamping operations. No dispersed phase was formed when aged at t = 50 °С in both optical metallography and scan electron microscopy cases. The non-uniformity of dispersed phase distribution inside a grain rises at initial aging stages with a holding time less than 1 hour at 100, 150 and 200 °С and decreases with a further increase in the holding time up to 4 hours. No correlation was observed between the uniformity of phase distribution and the stamping number. The chemical composition of phases has a greater effect on the formability and changes depending on a heat treatment mode: annealing and natural aging primarily lead to the θ and S phase precipitation; aging at temperatures below 150 °С with a holding time less than 1 hour lead to the θ, S and T phase precipitation; θ phase appears after aging at temperatures over 150 °C with long holding times.

aluminium alloy, structure, stamping number, aging, dispersed inclusions, phase composition

1. Kablov E.N., Antipov V.V., Senatorova O.G. Sloistye alyumostekloplastiki SIAL-1441 i sotrudnichestvo s AIRBUS i TU DELFT [Layer aluminium glass plastics SIAL-1441 and collaboration with AIRBUS and TU DELFT]. Tsvetnye metally. 2013. No. 9 (849). P. 50—53.

2. Kotik H.G., Perez Ipiña J.E. Short-beam shear fatigue behavior of fiber metal laminate (Glare). Int. J. Fatigue. 2017. Vol. 95. Р. 236—242.

3. Grechnikov F.V., Antipov V.V., Erisov Ya.A., Grechnikova A.F. Povyshenie tekhnologichnosti alyumostekloplastikov putem formirovaniya v listakh iz splava V95 effectivnoi kristallograficheskoi tekstury [Aluminium-glass plastic technological ability increasing via formation in alloy V95 sheets of effective crystallographic texture]. Izvestiya vuzov. Tsvetnaya metallurgiya. 2014. No. 6. P. 38—43.

4. Postnov A.V., Postnov V.I., Kazakov I.A. Osobennosti tekhnologii formovaniya profil’nykh konstruktsii iz metallopolimernykh kompozitsionnykh materialov [Features of profile constructions forming from metal-polymer composite materials]. Izvestiya Samarskogo nauchnogo tsentra RAN. 2009. Vol. 11. No. 3 (2). P. 499—508.

5. Bikakis G.S.E., Savaidis A. FEM simulation of simply supported GLARE plates under lateral indentation loading and unloading. Theor. Appl. Fracture Mech. 2016. Vol. 83. P. 2—10.

6. Biswas A., Siegel D.J., Seidman D.N. Compositional evolution of Q-phase precipitates in an aluminum alloy. Acta Mater. 2014. No. 75. P. 322—336.

7. Cheng S., Zhao Y.H., Zhu Y.T., Ma E. Optimizing the strength and ductility of fine structured 2024 Al alloy by nano-precipitation. Acta Mater. 2007. No. 55. P. 5822— 5832

8. Zhong H., Rometsch P.A., Cao L., Estrin Yu. The influence of Mg/Si ratio and Cu content on the stretch formability of 6xxx aluminium alloys. Mater. Sci. Eng. A. 2016. No. 651. P. 688—697.

9. Xu X., Zhao Yu., Ma B., Zhang J., Zhang M. Rapid grain refinement of 2024 Al alloy through recrystallization induced by electropulsing. Mater. Sci. Eng. A. 2014. No. 612. P. 223—226.

10. Rudskoi A.I., Kolbasnikov N.G., Ringinen D.A. Poluchenie submikronnoi i nanokristallicheskoi struktury metallov metodami goryachei i teploi deformatsii [Receiving of submicron and nanocrystalline structure by hot and warm deformation methods]. Nauchno-tekhnicheskie vedomosti Sankt-Peterburgskogo gosudarstvennogo politekhnicheskogo universiteta. 2011. No. 123. P. 191—205.

11. Kolbasnikov N.G., Kondrat’ev S.Yu. Struktura. Entropiya. Fazovye prevrashcheniya i svoistva metallov [Structure. Entropy. Phase transformation and properties of metals]. Sankt-Peterburg: Sankt-Peterburgskii gos. politekhnicheskii universitet, 2006.

12. Yi G., Littrell K.C., Poplawsky J.D., Cullen D.A., Sundberg E., Free M.L. Characterization of the effects of different tempers and aging temperatures on the precipitation behavior of Al—Mg (5.25 at.%)—Mn alloys. Mater. Design. 2017. Vol. 118. P. 22—35.

13. Mal’tsev M.V. Metallografiya promyshlennykh tsvetnykh metallov i splavov [Metallography of non-ferrous metals and alloys]. Moscow: Metallurgiya, 1970.

14. Kolachev B.A., Livanov V.A., Elagin V.I. Metallovedenie i termicheskaya obrabotka tsvethykh metallov i splavov [Metal science and heat treatment of non-ferrous metals and alloys]. Moscow: Metallurgiya, 2001.

15. Cochard A., Zhu K., Joulié S., Douin J., Huez J., Robbiola L., Sciau P., Brunet M. Natural aging on Al—Cu—Mg structural hardening alloys — investigation of two historical duralumins for aeronautics. Mater. Sci. Eng. A. 2017. Vol. 690. P. 259—269.

16. Abúndez A., Pereyra I., Campillo B., Serna S., Alcudia E., Molina A., Blanco A., Mayén J. Improvement of ultimate tensile strength by artificial ageing and retrogression treatment of aluminium alloy 6061. Mater. Sci. Eng. A. 2016. Vol. 668. P. 201—207

17. Lia X.M., Starink M.J. Identification and analysis of intermetallic phases in overaged Zr-containing and Cr-containing Al—Zn—Mg—Cu alloys. J. Alloys Compd. 2011. Vol. 509. No. 2. P. 471—476.

18. Lu Ya., Wang J., Li X., Chen Y., Zhou D., Zhou G., Xu W. Effect of pre-deformation on the microstructures and properties of 2219 aluminum alloy during aging treatment. J. Alloys Compd. 2017. Vol. 699. P. 1140—1145.

19. Strobel K., Lay M.D.H., Easton M.A., Sweet L., Zhu S., Parson N.C., Hill A.J. Effects of quench rate and natural ageing on the age hardening behaviour of aluminium alloy AA6060. Mater. Charact. 2016. Vol. 111. P. 43—52.

20. Hannard F., Pardoen T., Maire E., Bourlot C. Le, Mokso R., Simar A. Characterization and micromechanical modelling of microstructural heterogeneity effects on ductile fracture of 6xxx aluminium alloys. Acta Mater. 2016. Vol. 103. P. 558—572.

21. Song Y.F., Ding X.F., Xiao L.R., Zhao X.J., Cai Z.Y., Guo L., Li Y.W., Zheng Z.Z. Effects of two-stage aging on the dimensional stability of Al—Cu—Mg alloy. J. Alloys Compd. 2017. Vol. 701. P. 508—514.