Abstract:Al-6Zn-2.5Mg-1.8Cu alloy ingots were prepared by squeeze casting under different specific pressures, and the fresh ingot with best mechanical properties was solid hot extruded. With the increase of the specific pressure from 0 to 250 MPa, the dendrites became round and small. Because the applied pressure increased the solid solubility of alloying elements, the number of MgZn₂ phases decreased. When the specific pressure increased from 250 MPa to 350 MPa, the grain size increased. After solid hot extrusion, the α(Al) grains were refined obviously and the MgZn₂ phases were uniformly dispersed in the microstructure. After solid hot extrusion, the ultimate tensile strength was 605.67 MPa and the elongation was 8.1%, which were improved about 32.22% and 15.71%, respectively, compared with those of the metal mold casting alloy. The fracture modes of the billet prepared by the metal mold casting and by squeeze casting were intergranular and quasi-cleavage fractures, respectively, whereas, that of the solid hot extrusion was mainly dimple fracture. The refined crystalline strengthening was the main reason to improve the strength and elongation of alloy.

Key words: AlZn alloy; squeeze casting; solid hot extrusion; dynamic recrystallization; microstructure; mechanical properties