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The impact toughness of a hypereutectic Al–23mass% Si alloy was improved by rotary-die equal-channel angular pressing (RD-ECAP). The alloy was successfully processed by RD-ECAP at high temperatures of 673K and 623K. The absorbed energy as measured by Charpy impact tests significantly increased with increasing the number of RD-ECAP passes, and finally reached 13.0kJ/m² after 32 passes. This value is 18 times higher than that of the as-cast Al–23mass% Si alloy and 41% higher than that of the as-cast eutectic Al–11mass% Si alloy. The grain or grain fragment size is about 150nm. In addition, most of the large primary silicon particles (over 50μm) were broken in the first 4 passes, and the primary silicon particle sizes decreased with increasing the pressing passes. These results indicate that the multipass RD-ECAP is effective in improving impact toughness through refining grains and changing the …