Assessment of the effect of cooling rate on dendrite coherency point and hot tearing susceptibility of AZ magnesium alloys using thermal analysis

Abstract

ABSTRACTDendrite coherency point (DCP) is an important parameter for examining the solidification structure and castability of alloys. In this research, the DCP of AZ magnesium alloys (AZ31, AZ61 and AZ91) is measured in the range of 0.22 °Cs−1 to 8.13 °Cs−1 cooling rates using the two-thermocouple thermal analysis technique. The results show that when cooling rate increased, temperature interval of coherency (TN – TDCP) and coherency time (tDCP) are decreased; and it can postpone dendrite coherency. Also, by increasing the cooling rate, solid fraction at dendrite coherency increases initially and then decreases at higher cooling rates. To estimate the hot tearing susceptibility, Clyne and Davies’ criterion is used. Hot tearing susceptibility calculations exhibit initially reduce by increasing the cooling rate and then it increases at higher cooling rates. These results were explained based on the solidification principles.