HAZ liquation cracking susceptibilities of LD_2 and 6061 aluminum alloys are investigated using hot tensile test with Gleeble-1500 and varestraint test. The experimental results are consistent with that of production. HAZ liquation cracking susceptibility of the LD_2 alloy is higher than that of the 6061 alloy. The results of AES and EPMA show that when the two alloys are heated fast, the solutes Si and Mg are segregated at the grain boundary, however, the segregation of Si in the LD_2 alloy is more serious. There are many high Si containing, high Si and high Mg containing phases as well as high Si, high Mg and high Cu containing phase in the LD_2 alloy. The liquation temperature of alloy and the solidification temperature of liquid film along grain boundary are lowered due to the constitutional liquation of these phases during welding. Therefore, HAZ liqation cracking susceptibility of the LD_2 alloy is higher than that of the 6061 alloy.
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