Abstract
The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α1-Mg phases, α2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure (α-Mg+MgZn2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1Cr alloy was treated at 585 °C for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.
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Xiao-feng Huang Male, born in 1971, Ph.D, Associate professor. His research interests mainly focus on magnesium alloys and semi-solid forming. To date, he has published over 70 papers.
This work was financially supported by the National Natural Science Foundations of China (51464032).
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Huang, Xf., Ma, Yj., Zhang, Qq. et al. Effects of trace Cr on as-cast microstructure and microstructural evolution of semi-solid isothermal heat treatment ZC61 magnesium alloy. China Foundry 16, 53–62 (2019). https://doi.org/10.1007/s41230-019-8112-z
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DOI: https://doi.org/10.1007/s41230-019-8112-z
Key words
- ZC61 magnesium alloy
- Cr content
- semi-solid isothermal heat treatment
- non-dendritic microstructure
- microstructural evolution