THIXOFORGING OF ALUMINUM-ALLOYS

A new process for the forming of metal alloys into net or near-net shapes by forging-type operations was investigated. The process, denoted as thixoforging, uses a partially solidified, vigorously agitated rheocast metal as initial charge material. It was shown that intermittent operation of the slurry producer coupled with direct transfer of the semi-solid charge to the lower die of the forging press permits production of sound heat-treatable components that are free of entrapped oxides and which have excellent static and dynamic properties. Commercial 2024 aluminum-base alloy was used in the investigation. The solution heat treatment response of rheocast ingots and the structure and properties of thixoforged parts of the alloy were compared with conventionally solidified ingots and with forgings made from a completely liquid initial charge respectively. It was found that the initial spheroidal rheocast structure contains less non-equilibrium second phase and solutionizes more rapidly than the plate-like dendritic structure. The disk-shaped parts 0.12 m in diameter and 0.025-0.04 m high produced from both rheocast and liquid charge materials respond to heat treatment and possess properties comparable with those of the wrought alloy. For example, the tensile properties of the thixoforged parts in the T-6 condition were as follows: yield strength, approximately 35 kgf mm-2; ultimate tensile strength, 46.4 kgf mm-2; elongation, 11.2%. These values are slightly lower than those measured on squeeze-cast parts made in this study. The fatigue properties of the thixoforged parts, however, were slightly superior. © 1979.