Evaluation of hot cracking in AZ91E and AE42 magnesium alloys

In this study, the hot cracking susceptibility of AZ91E and AE42 magnesium alloys was assessed using the moving torch Varestraint test method. Plates of 3 mm thickness were sliced from AZ91E and AE42 ingots and subsequently tested. Quantitative cracking data in terms of maximum crack length was used for evaluating the cracking susceptibility. Scanning electron microscopy (SEM) was carried out and the results suggest that AE42 showed a higher resistance to hot cracking in comparison to the AZ91E alloy. This was attributed to the difference in microstructure between the two alloys. In the fusion zone and heat affected zone of AE42, the brittle needle-like Al 11RE 3 phase was seen to decompose to the more ductile particle-like Al 2RE phase, thereby increasing the alloy's resistance to hot cracking. In contrast, SEM fractography revealed that brittle Al 6Mn and Mg 17Al 12 intermetallic particles segregated to grain boundaries and triggered hot cracking in AZ91E. © 2012 Canadian Institute of Mining, Metallurgy and Petroleum.