National University of Science and Technology MISiS, Moscow, Russia¹ ; Baykov Institute of Metallurgy and Materials Science, Moscow, Russia²:

T. K. Akopyan, Senior Researcher at the Department of Metal Forming¹, Research Fellow at Laboratory No. 30², Candidate of Technical Sciences, e-mail: aktorgom@gmail.com

National University of Science and Technology MISiS, Moscow, Russia:

N. V. Letyagin, Lead Project Engineer at the Department of Metal Forming, Candidate of Technical Sciences

Baykov Institute of Metallurgy and Materials Science, Moscow, Russia:
A. G. Padalko, Head of Laboratory No. 30, Doctor of Chemical Sciences
M. S. Pyrov, Research Engineer at Laboratory No. 30

This paper looks at the effect of high external pressure that is applied during barothermal processing of aluminium alloy Al – 7 Si – 3.5 Cu – 0.1 Sn of the А319 type microalloyed with tin. Through differential barothermal analysis conducted at the pressure of 100 MPa, it was found that the phase transition temperatures of the alloy rose from 8 to 11 ^oC. Through scanning electron microscopy, it was established that, after heat treatment at the temperature of 505 ^oC and barothermal processing at the pressure of 100 MPa/505 ^oC/3 h, as the result of thermally activated processes of fragmentation and spheroidization, some microstructural elements – namely, eutectic crystals of the proeutectoid constituents (Si and α(Al(MnFe)Si)) – acquire a more compact morphology, close to the spherical one, with the average particle diameter of 5 to 10 μm. Uniaxial tensile testing of alloy specimens subjected to barothermal processing followed by strengthening T6 heat treatment (for maximum strength), revealed a high level of mechanical properties: ultimate strength – 408 MPa, yield strength — 334 MPa, elongation — 3.1%, compared with the standard level typical of this group of alloys that are not microalloyed with tin. Analysis of the fracture surface in specimens after uniaxial tensile testing revealed standard tiny pits with second-phase particles at the bottom of the pits. The presence of a trace eutectic constituent in the studied concentration range does not lead to brittle intercrystalline fracture. Nor the presence of excessive porosity typical of castings that were not subjected to hot isostatic pressing caused the fracture. By means of scanning electron microscopy, the authors examined the fine structure of the alloy after a full heat treatment cycle, which included HIP followed by T6 heat treatment. It was found that the decomposition products – lamellar precipitates of the metastable θ'-phase, which are ~(50–70) nm long and 3–5 nm thick plates – acquire a disperse structure, with the distribution density being high. Due to the resultant combination of properties, the new group of Al – Si – Cu – Sn alloys can potentially be used for making critical parts, including new generation internal combustion engines.
This research was funded under Governmental Assignment 075-00715-22-00(DBA, DSC, HIP). The structural study was conducted with the help of the equipment of the Shared Knowledge Centre Materials Science and Metallurgy, purchased using the funding provided by the Ministry of Science and Higher Education of the Russian Federation (GK 075-15-2021-696).

1. Polmear I. J. Light alloys: from traditional alloys to nanocrystals. Butterworth-Heinemann. Oxford, 2006. 421 p.
2. Li Z., Limodin N., Tandjaoui A., Quaegebeur P., Witz J.-F. et al. In-situ 3D characterization of tensile damage mechanisms in A319 aluminium alloy using X-ray tomography and digital volume correlation. Materials Science and Engineering: A. 2020. Vol. 794. 139920.

3. Rincon E., Lopez H. F., Manchac H. Temperature effects on the tensile properties of cast and heat treated aluminum alloy A319. Materials Science and Engineering: A. 2009. Vol. 519. pp. 128–140.
4. Mo D.-F., He G.-Q., Hu Z.-F., Liu X.-S., Zhang W.-H. Effect of microstructural features on fatigue behavior in A319-T6 aluminum alloy. Materials Science and Engineering: A. 2010. Vol. 527, Iss. 15. pp. 3420–3426.
5. Akopyan T. K., Belov N. A., Letyagin N. V., Milovich F. O., Lukyanchuk A. A. et al. Influence of indium trace addition on the microstructure and precipitation hardening response in Al – Si – Cu casting aluminum alloy. Materials Science and Engineering: A. 2022. Vol. 831. 142329.
6. Akopyan T. K., Belov N. A., Lukyanchuk A. A., Letyagin N. V., Milovich F. O. et al. Characterization of structure and hardness at aging of the A319 type aluminum alloy with Sn trace addition. Journal of Alloys and Compounds. 2022. Vol. 921. 166109.
7. Shurkin P. K., Akopyan T. K., Letyagin N. V. Effect of indium microaddition on the structure and strengthening of binary Al – Cu alloys. Physics of Metals and Metallography. 2021. Vol. 122. pp. 807–813.
8. Houria I. M., Nadot Y., Fathallah R., Roy M., Maijer D. M. Influence of casting defect and SDAS on the multiaxial fatigue behaviour of A356-T6 alloy including mean stress effect. International Journal of Fatigue. 2015. Vol. 80. pp. 90–102.
9. Ceschini L., Morri A., Toschi S., Seifeddine S. Room and high temperature fatigue behaviour of the A354 and C355 (Al – Si – Cu – Mg) alloys: role of microstructure and heat treatment. Materials Science and Engineering: A. 2016. Vol. 653. pp. 129–138.
10. Wang Q. G., Davidson C. J. Solidification and precipitation behaviour of Al – Si – Mg casting alloys. Journal of Materials Science. 2001. Vol. 36. pp. 739–750.
11. Han S.-W., Kumai S., Sato A. Effects of solidification structure on short fatigue crack growth in Al – 7% Si – 0.4% Mg alloy castings. Materials Science and Engineering: A. 2002. Vol. 332. pp. 56–63.
12. Mansurov Yu. N., Aksenov A. A., Reva V. P. Influence of the chill-mold casting process on the structure and properties of aluminum alloys with eutectic constituents. Tsvetnye Metally. 2018. No. 5. pp. 77–81.
13. Wang Q. G., Apelian D., Lados D. A. Fatigue behavior of A356-T6 aluminum cast alloys. Part I. Effect of casting defects. Journal of Light Metals. 2001. Vol. 1. pp. 73–84.
14. Bufe`re J.-Y., Savelli S., Jouneau P. H., Maire E., Fougeres R. Experimental study of porosity and its relation to fatigue mechanisms of model Al – Si7 – Mg0.3 cast Al alloy. Materials Science and Engineering: A. 2001. Vol. 316, Iss. 1-2. pp. 115–126.
15. Hafenstein S., Werner E. Pressure dependence of age-hardenability of aluminum cast alloys and coarsening of precipitates during hot isostatic pressing. Materials Science and Engineering: A. 2019. Vol. 757. pp. 62–69.
16. Cai C., He S., Li L., Teng Q., Song B. et al. In-situ TiB/Ti – 6 Al – 4 V composites with a tailored architecture produced by hot isostatic pressing: microstructure evolution, enhanced tensile properties and strengthening mechanisms. Composites. Part B. Engineering. 2019. Vol. 164. pp. 546–558.
17. Yu H., Li F., Wang Z., Zeng X. Fatigue performances of selective laser melted Ti – 6 Al – 4 V alloy: influence of surface finishing, hot isostatic pressing and heat treatments. International Journal of Fatigue. 2019. Vol. 120. pp. 175–183.
18. Cai C., Song B., Xue P., Wei Q., Wu J.-m. et al. Effect of hot isostatic pressing procedure on performance of Ti6Al4V: surface qualities, microstructure and mechanical properties. Journal of Alloys and Compounds. 2016. Vol. 686. pp. 55–63.
19. Kreitcberg A., Brailovski V., Turenne S. Effect of heat treatment and hot isostatic pressing on the microstructure and mechanical properties of Inconel 625 alloy processed by laser powder bed fusion. Materials Science and Engineering: A. 2017. Vol. 689. pp. 1–10.
20. Takata N., Kodaira H., Sekizawa K., Suzuki A., Kobashi M. Change in microstructure of selectively laser melted AlSi10Mg alloy with heat treatments. Materials Science and Engineering: A. 2017. Vol. 704. pp. 218–228.
21. Fousova M., Dvorský D., Michalcova A., Vojtech D. Changes in the microstructure and mechanical properties of additively manufactured AlSi10Mg alloy after exposure to elevated temperatures. Materials Characterization. 2018. Vol. 137. pp. 119–126.
22. Li X. P., Wanga X. J., Saunders M., Suvorova A., Zhang L. C. et al. A selective laser melting and solution heat treatment refined Al – 12 Si alloy with a controllable ultrafine eutectic microstructure and 25% tensile ductility. Acta Materialia. 2015. Vol. 95. pp. 74–82.
23. Prashanth K. G., Scudino S., Klauss H. J., Surreddi K. B., Lober L. et al. Microstructure and mechanical properties of Al – 12 Si produced by selective laser melting: effect of heat treatment. Materials Science and Engineering: A. 2014. Vol. 590. pp. 153–160.
24. Ma P., Prashanth K. G., Scudino S., Jia Y., Wang H. et al. Influence of annealing on mechanical properties of Al – 20 Si processed by selective laser melting. Metals. 2014. Vol. 4. pp. 28–36.
25. Kimura T., Nakamoto T. Thermal and mechanical properties of commercial-purity aluminum fabricated using selective laser melting. Materials Transactions. 2017. Vol. 58, Iss. 5. pp. 799–805.
26. Kempen K., Thijs L., Van Humbeeck J., Kruth J. P. Mechanical properties of AlSi10Mg produced by selective laser melting. Physics Procedia. 2012. Vol. 39. pp. 439–446.
27. Zhai Y., Huang B., Mao X., Zheng M. Effect of hot isostatic pressing on microstructure and mechanical properties of CLAM steel produced by selective laser melting. Journal of Nuclear Materials. 2019. Vol. 515. pp. 111–121.
28. Yu H., Li F., Wang Z., Zeng X. Fatigue performances of selective laser melted Ti – 6 Al – 4 V alloy: influence of surface finishing, hot isostatic pressing and heat treatments. International Journal of Fatigue. 2019. Vol. 120. pp. 175–183.
29. Hirata T., Kimura T., Nakamoto T. Effects of hot isostatic pressing and internal porosity on the performance of selective laser melted AlSi10Mg alloys. Materials Science & Engineering: A. 2020. Vol. 772. 138713.
30. Wang Y., Shi J. Effect of hot isostatic pressing on nanoparticles reinforced AlSi10Mg produced by selective laser melting. Materials Science & Engineering: A. 2020. Vol. 788. 139570.
31. Spierings A. B., Dawson K., Dumitraschkewitz P., Pogatscher S., Wegener K. Microstructure characterization of SLM-processed Al – Mg – Sc – Zr alloy in the heat treated and HIPed condition. Additive Manufacturing. 2018. Vol. 20. pp. 173–181.
32. Padalko A. G., Talanova G. V., Ponomareva E. Yu., Talyat-Kelpsh V. V., Shvorneva L. I. et al. Phase transformations at high pressures and temperatures and the structure of hypoeutectic 1 Ni – 99 Al alloy. Metally. 2012. No. 5. pp. 46–53.
33. Dedyaeva E. V., Akopyan T. K., Padalko A. G., Talanova G. V., Shvorneva L. I. et al. Understanding the effect of the baric component on the phase transformations and structure of Al – 12 at % Si alloy. Neorganicheskie materialy. 2014. Vol. 50. pp. 719–725.
34. Hwang J. Y., Doty H. W., Kaufman M. J. The effects of Mn additions on the microstructure and mechanical properties of Al – Si – Cu casting alloys. Materials Science & Engineering: A. 2008. Vol. 488, Iss. 1-2. pp. 496–504.
35. Glazoff M., Khvan A., Zolotorevsky V., Belov N., Dinsdale A. Casting Aluminum Alloys. 2^nd edition, Butterworth-Heinemann. Oxford, 2018. 544 p.
36. Akopyan T. K., Belov N. A., Padalko A. G., Letyagin N. V., Avksentyeva N. N. Analysis of the effect of hydrostatic pressure on the nonvariant eutectic transformation in Al – Si, Al – Cu, and Al – Cu – Si systems. Physics of Metals and Metallography. 2019. Vol. 120. pp. 593–599.
37. Padalko A. G., Pyrov M. S. Thermal and barothermal treatment, microstructure, and properties of an Al – 8 Si – 3.5 Cu – 0.2 Mn alloy. Russian Metallurgy (Metally). 2020. No. 9. pp. 1002–1009.
38. Bourgeois L., Dwyer C., Weyland M., Nie J., Muddle B. C. Structure and energetics of the coherent interface between the θ' precipitate phase and aluminium in Al – Cu. Acta Materialia. 2011. Vol. 59, Iss. 18. pp. 7043–7050.
39. Bourgeois L., Dwyer C., Weyland M., Nie J. F., Muddle B. C. The magic thicknesses of θ' precipitates in Sn-microalloyed Al – Cu. Acta Materialia. 2012. Vol. 60. pp. 633–644.