High temperature phase stabilized microstructure in Mg–Zn–Sn alloys with Y and Sb additions
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Mg–Zn–Sn alloys exhibit poor structural stability at elevated temperatures that restricts utilization of these alloys. Small additions of alloying elements forming high temperature phases (HTP) were used to improve the structural stability of the Mg–Zn–Sn alloy. The main goal of this work was to investigate the microstructure evolution of the Mg–Zn–Sn-alloy with additions of Y and Sb during a wide scope of heat treatments, and to elucidate peculiarities of an HTP-stabilized microstructure. In order to clarify the substructure features and phase precipitation after each step of the heat treatment, XRD, TEM, SEM and EDS analyses were applied. It was found that in the dendrite structure formed during solidification, HTP-particles are concentrated in the inter-dendrite regions. Solution treatment of the as-cast structure at 440 °C for 96 h lead to the formation of α-Mg grains of 50–80 μm in diameter with a characteristic substructure. The presence of HTP-particles prevented dislocation recovery and movement of dislocation walls during solution treatment, and by this way restricted annihilation of grain boundaries between dendrites of close orientation, and lead to the formation of a substructure with sub-grains of 20–30 μm. The sub-grain boundaries are pinned by HTP-particles and are strengthened by the MgZn2 and Mg2Sn binary precipitates during aging. Precipitate depleted zones formed near grain- and sub-grain boundaries during aging were bordered by a “crust” of enlarged binary particles. Such pinned sub-grain microstructure provides a high structural stability of the alloys at elevated temperatures.
KeywordsSolution Treatment Precipitation Hardening High Temperature Phase HFC134A Solution Treated Alloy
The study was partially supported by the Fund for the Promotion of Research at the Technion. The foundation is acknowledged for its support.
- 1.Cohen S, Goren-Muginstein GR, Abraham S, Dehm G, Bamberger M (2003) Phase formation, precipitation and strengthening mechanisms in Mg–Zn–Sn and Mg–Zn–Sn–Ca alloys. In: Proceedings of the TMS annual meeting, San Diego, CA, 2 March 2003, p. 301Google Scholar
- 3.Rashkova B, Keckes J, Levi G, Gorny A, Bamberger M, Dehm G (2006) Microstructure Evolution and Phase Formation in Novel Mg–Zn-Based Alloys, Magnesium. In: Kainer KU (ed) Proceedings of the 7th International conference on magnesium alloys and their applications. DGM, Dresden, Germany, 6–9 November 2006, p 486Google Scholar
- 8.Gorny A, Goren-Muginstein GR, Katsman A, Dehm G, Rashkova B, Bamberger M (2006) The influence of Y additions on precipitation sequence in Mg–Zn–Sn based alloy. In: Proceedings of the TMS annual meeting, San Antonio, Texas, USA, 12–16 March 2006, pp 387Google Scholar
- 9.Porter DA, Easterling KE (2004) Phase transformations in metals and alloys. CRC Press, Taylor&Francis Group, Boca Raton, FL, p 514Google Scholar