Evolution of the Microstructure and Microsegregation in Subrapidly Solidified Mg-6Al-4Zn-1.2Sn Magnesium Alloy

The evolution of the microstructure and microsegregation in a new type of Mg-6Al-4Zn-1.2Sn (wt%) cast magnesium alloy solidified at cooling rates from 4.5 x 10(1) degrees C s(-1)to 2.3 x 10(3) degrees C s(-1)is investigated. The results indicate that the secondary dendrite arm spacing and the average grain sizes decrease from 14.3 to 2.9 mu m and from 187 to 78 mu m, respectively, as the cooling rate increases from 4.5 x 10(1) degrees C s(-1)to 2.3 x 10(3) degrees C s(-1). The relationship between the secondary dendrite arm spacing (lambda(2)) and cooling rate (R) is fitted as lambda(2) = 69.7 x R-0.42. When the alloy solidifies in the range of cooling rates, a new quasi-crystalline I phase is formed due to faster solidification. The microsegregation ratios of Al, Zn, and Sn elements decrease significantly with the increase in cooling rate. Compared with the specimen solidified at 4.5 x 10(1) degrees C s(-1), the microsegregation ratios of Al, Zn, and Sn of that solidified at a cooling rate of 2.3 x 10(3) degrees C s(-1)decrease by 37.4%, 45.7%, and 31.6%, respectively.

Automated summary

The evolution of microstructure and microsegregation in a new Mg-6Al-4Zn-1.2Sn cast magnesium alloy solidified at different cooling rates was investigated. The results showed that the secondary dendrite arm spacing and grain sizes decreased with increasing cooling rate, forming a new quasi-crystalline I phase and significantly reducing the microsegregation ratios of Al, Zn, and Sn elements.