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Two cast noncombustible Mg–9Al–1Zn–1Ca alloys (composition in mass%) with coarse and fine initial microstructures were hot forged by compression at temperatures of 523–603 K and a true strain rate of 1–10−2 s−1. The compressive stress–strain curves for the two alloys were similar and typical of metals undergoing dynamic recrystallization (DRX). The alloy with the coarse initial microstructure suffered from edge crack formation during hot forging, while the alloy with the fine initial microstructure exhibited smooth peripheral surfaces after hot forging at temperatures of 573 K and above. The reduction of grain size by DRX was similar in the two hot-forged alloys, but the recrystallized volume fraction was lower in the alloy with the coarse initial microstructure. Insoluble second phases (seemingly Al2Ca) provide additional DRX sites, and thus it is expected that the finer initial cast microstructure will improve the microstructure in the resulting hot-forged Mg parts.

A hypereutectic Al-Si-Cu-Mg alloy billet was fabricated by a semi-solid forming method that combined a simple mechanical stirring treatment with the vertical semi-continuous casting process. Higher rotational speeds and higher casting temperatures during stirring yielded a finer as-cast structure and more uniform distribution of primary silicon particles in the matrix. However, these stirring conditions also led to transverse cracks on the billet surface. A mechanical vibration treatment using smaller amplitudes and lower frequencies during casting improved the cracked surface considerably, resulting in a structure comparable to that of the billet stirred at the same time.

In order to obtain a superior thixotropic property even in a high strength 7075 aluminum alloy, a billet of an Al-5.5%Zn-2.5%Mg-1.5%Cu alloy with a nondendritic fine-grained structure has been tried to produce by combining a simple mechanical stirring with the vertical semi-continuous casting process. We succeeded to get a good quality billet on the basis of the trials that had been carried out under the various stirring conditions, especially focussing on the position of a stirring rotor, the shape of a rotor and the volume of a stirring chamber. When the temperature within a stirring chamber was nearly constant just below the liquidus temperature and dropped drastically near the liquid-solid interface during casting, a long sound billet with relatively smooth surface could be produced. And the billet had not only a uniformly fine-grained structure with the average grain size of ∼30 μ m, but also little macroscopic segregation of the solute elements along the radius at the various positions of the billet.