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1 Journal of Achievements in Materials and Manufacturing Engineering

1 2013

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Cooling curve and microchemical phase analysis of rapidly quenched magnesium AM60B and AE44 alloys

Gesing A.J., Sokołowski J. H., Marchwica P.C., Blawert C., Jekl J., Kozdras M., Kasprzak M., Wood J.

Journal of Achievements in Materials and Manufacturing Engineering

2013

Vol. 58, nr 2

59--73

Purpose: Development of the understanding of the effect of the solidification rate with the alloy microstructures for the structural AM60B and the creep resistant AE44 Mg casting alloys. Design/methodology/approach: Tubular macro test samples of magnesium alloys AM60B and AE44 were melted and quenched at maximum instantaneous cooling rates ranging from -5°C/s to -500°C/s in the Universal Metallurgical Simulator and Analyzer (UMSA) Technology Platform while recording the temperature-time traces. Such rapid cooling rates are typical in water-cooled dies used in high pressure die casting (HPDC). Characteristic reactions on these curves corresponding to the formation of individual phases during solidification were quantified based on cooling curve analysis combined with metallographic and micro-chemical analysis, with the aid of literature data. Findings: The results indicate that these phases, their size and location in the microstructure, their chemistry and their relative proportions all change in response to the increase in the cooling rate. The results are drastically different for the two alloy systems studied. Solidification of AM60B alloy yields small, equiaxed α-Mg rosettes whose size is mostly independent of the cooling rate. These rosettes nucleate heterogeneously on Al8Mn5 phases that are first to form, and are surrounded by the eutectic structure of Mg and Mg17Al12. In contrast, the AE44 has very large α-Mg grains at all cooling rates. These grains are filled with Al11RE3 platelets or dendrites. Results suggest that the Al11Re3 phase is completely ineffective in heterogeneous nucleation of α-Mg grains. Originality/value: In this research the authors significantly extended the thermal analysis methodology. The specific results obtained on the structural and creep-resistant Mg casting alloys are of significant value to the development of automotive light metal structures and power train components as well as further development of solidification codes for the commercial HPDC process.