Hot ductility behavior and HAZ hot cracking susceptibility of 7475-T7351 aluminum alloy

The elevated temperature mechanical properties and hot crack susceptibility of the aluminum alloys, 7475-T7351 and 7005-T1 were evaluated using a Gleeble hot-ductility test. The 7475 alloy exhibited lower hot ductility and strength, significantly poorer ductility recovery on cooling from the nil-strength temperature, considerably wider brittle temperature range (BTR) and crack susceptible region (CSR), and thus greater susceptibility to heat-affected zone (HAZ) hot cracking, as compared to the 7005 alloy. Longitudinal samples of 7475 had a lower crack susceptibility than short-transverse 7475 samples. The results showed good agreement with those of the spot-Varestraint tests. Scanning electron microscopy (SEM) revealed that the ductility loss was accompanied by fracture transition from ductile transgranular mode to brittle intergranular mode. The HAZ hot cracking in alloy 7475 due to the loss of ductility was primarily caused by liquation of low-melting-point grain boundary segregates or eutectics that contained high amounts of Mg, Cu, and Zn.