It is economically advantageous to cast wrought aluminum alloys directly into near-net-shape components.The objective of the present work is to take advantage of the rheoforming with 7075 alloy to improve the competitiveness of this emerging technology in the manufacture of wrought aluminum alloy.High quality semi-solid slurry was produced,in which primary α(Al) presents in diameter of 62 μm and shape factor of 0.78 and features no eutectics entrapped.Higher forming pressure results in small grain size,improved shape factor and higher density.Especially,rheoforming can effectively reduce the occurrence of hot tearing.The average yield strength and elongation of the rheoformed samples in the T6 condition are 483 MPa and 8%,respectively.
The isothermal coarsening behavior of primary solid particles in A356 aluminum alloy semi-solid slurry produced by angular oscillation (AO) technique was investigated.The comparison between the calculation and experimental results shows good quantitative agreement with Lifshitz-Slyozov-Wagner theory.The results show that the variation in shape factor and solid fraction is not significant,the average particle size increases with increasing holding time at the expense of the particle density.Ostwald repining is most likely the predominant growth mechanism in the AO-treated semi-solid slurry during rheocasting.The differences of coarsening occurred in rheocasting and partial re-melting process were also discussed.
The experimental and analytical approaches were taken to investigate the non-dendritic microstructure formation and evolution of AlSi9Cu3 alloy during rheocasting.The results show that the globular primary α(Al) particles free of entrapped eutectic form after rheocasting for 3 s,and could be morphologically stabilized during subsequent growth.The fine and globular particles underwent a coarsening process under quiescently continuous cooling in which the particle density decreases,the solid fraction increases,the average particle size increases with the increase of solidification time at a rate that closely followed the classical Ostwald ripening.
