Semi-solid metal processing method and a process for casting alloy billets suitable for that processing method

A method of processing semi-solid metals comprising the steps of:

• (a) casting a melt of a hypo-eutectic aluminum alloy having a composition at or above maximum solubility limits into a billet-forming mold, the melt being at a temperature as it is cast into said mold which exceeds the liquidus line temperature of the alloy, but is not higher by more than 30.degree. C. of the liquidus line temperature;
• (b) cooling said melt to solidify said alloy within said billet-forming mold at a cooling rate of at least 1.0.degree. C./sec in a solidification zone so as to form a billet;
• (c) heating said billet to a temperature above the eutectic point of said alloy;
• (d) selecting a holding time and a temperature such that the billet has a liquid-phase content of between 20% and 80% and that primary crystals thereof are spheroidized, to form a semi-solid billet;
• (e) supplying the semi-solid billet from step (d) to a shaping mold;
• and
• (f) forming the billet from step (e) into a shape under pressure.

A method of processing semi-solid metals comprising the steps of:

• (a) casting a melt of (i) a magnesium alloy containing 0.005 to 1% Sr or 0.05 to 0.3% Ca or 0.01 to 1.5% Si and 0.005 to 1% Sr or (ii) an aluminum alloy containing 0.001 to 0.01% B and 0.005 to 0.30% Ti or 0.001 to 0.1% B, 0.005 to 0.30% Ti and 4 to 6% Si, and having a composition within maximum solubility limits, into a billet-forming mold, the melt being at a temperature as it is cast into said billet-forming mold which exceeds the liquidus line temperature of the alloy, but is not higher by more than 30.degree. C. of the liquidus line temperature;
• (b) cooling said melt to solidify said alloy within said billet-forming mold at a cooling rate of at least 1.0.degree. C./sec in a solidification zone to form a billet;
• (c) heating said billet within said billet-forming mold from the solubility line temperature to the solidus line temperature of the alloy at a rate of at least 0.5.degree. C./minute;
• (d) further heating the billet from step (c) to a temperature exceeding the solidus line temperature of the alloy;
• (e) maintaining the billet from step (d) at the temperature in step (d) for 5 to 60 minutes, thereby spheroidizing primary crystals thereof;
• (f) further heating said billet from step (e) to a molding temperature below the liquidus line temperature of the alloy to form a semi-solid billet;
• (g) feeding the semi-solid billet from step (f) into a shaping mold;
• and
• (h) forming the billet into a shape under pressure.