Achieving ultra-fine grains in AZ61 Mg alloy by friction stir processing

In order to obtain fine-microstructure magnesium alloys with superior mechanical properties, AZ61 alloy is processed by friction stir processing combined with rapid heat sinking in this study. Ultrafine-grain microstructure with average size less than 300 nm was observed in the resultant AZ61 alloy. The mean microhardness of the ultrafine-grain region reached 120 similar to 130 HV, twice that of the AZ61 substrate. All these results demonstrate clearly that under a cooling rate high enough, ultrafine-grain Structure in AZ61 alloy with superior mechanical properties can be produced by one pass friction stir processing via dynamic recrystallization.