Hot cracking of binary Mg–Al alloy castings

Hot cracking of binary Mg–Al alloys in permanent mold casting was studied. The alloys contained from 0.25 to 8 wt.% Al. The hot cracking susceptibility was evaluated using constrained rod casting in a steel mold, in which cracking was induced by enlarging the ends of the rods to keep them from contracting freely during solidification. The hot cracking susceptibility was evaluated based on both the widths and locations of cracks in the resultant castings. The curve of the crack susceptibility versus the Al content showed a peak near 1 wt.% Al. The onset of hot cracking during casting was detected by connecting a load cell to a rod solidifying in a similar steel mold and recording the temperature at the end of the rod where cracking occurred. A cracking susceptibility coefficient based on the time at the onset of cracking was found to correlate well with the crack susceptibility curve.