Liquid Penetration Phenomenon of Gas Atomized Powders during Semi-solid Rolling

Under an H2 atmosphere, the green strips were prepared from Al-5.8Zn-1.63Mg-2.22Cu-0.12Zr(wt%) powder by the semi-solid rolling process. The effects of different holding time at 610 °C (i.e. liquid phase fraction is fs 53 %) on the microstructure evolution, especially the liquid penetration phenomenon of the strips were investigated. Results show that a higher degree of liquid penetration will accelerate the disappearance of the primary particle boundaries in the plane of contact, and a more obvious change of powder primary boundaries will occur. With increasing of holding time from 10 min to 30 min at 610 °C, the amount of η (MgZn2) phase decreases and more particles Al2Cu precipitate at grain boundaries. The optimum holding time for Al-5.8Zn-1.63Mg-2.22Cu-0.12Zr (wt%) powder semi-solid rolled at 610 °C is suggested to be between 20 min to 30 min. The present experimental analysis indicates that the strips with high mechanical properties can be produced by optimizing semi-solid powder rolling process.