The improved microstructures and properties of 7075 alloys produced by a water-cooling centrifugal casting method

A centrifugal water-cooling casting method was used to cast a 7075 alloy with the aim of refining the grain and inclusion size and improving mechanical properties in the wrought condition. Conventional ingot casting methods were also used and investigated for comparison with the centrifugal casting method. The results show that by the centrifugal casting method, a small equiaxed grain size, 17 microns, is obtained in as-cast condition. Only 50 min are required for material homogenization. After rolling to obtain sheet, a grain size of 15 x 8 x 6 microns and an inclusion size of 2 to 3 microns are achieved. Fine-grained centrifugal-cast 7075 alloy exhibits higher strength than the ingot-cast one in the early stages of aging but poorer in the latter stages. However, its ductility and combination of strength and ductility is superior to the ingot-cast ones at all aging times. The reduction in strength in the latter aging stages for the fine-grained structure arises from its higher volume fraction of soft precipitate free zones. The improved ductility is attributed to the higher fraction of transgranular fracture, higher transgranular fracture strain, and intergranular fracture strain. (Author)