A 3D FEM model of Al-7Zn-3Mg wrought aluminum alloy slab ingot with 450 mm×1 620 mm was established.Both thermal and stress fields of a slab billet were obtained via simulating casting conditions without wiper and with various wiper inserting positions

and the Clyne-Davies hot cracking model was used to calculate and evaluate the HCS（hot cracking susceptibility）of the ingots.The results reveal that the wiper has a little effect on both macrosegregation and HCSwhen it is placed at a height near the bottom of the solidifying end.The macrosegregation and HCSare increased greatly with the wiper setting position increases.When the wiper is inserted near the bottom of the sump

the macrosegregation and HCSof the billet are increased significantly.In order to suppress macrosegregation and hot cracking

it is suggested to insert the wiper at about 10 cm below the bottom of the sump.In contrast

the thermal stress of the ingot is decreased with the wiper setting position increases.In addition

the effect of an innovative stepwise wiper has also been analyzed.The results show that the new wiper can decrease the thermal stress by 4.5 MPa of the ingot than the conventional flat one and without negative effect on both macrosegregation and hot cracking tendency.