Grain Size Refinements of Mg Alloys (AZ61, AZ91, ZK60) by HDDR Treatment

Abstract

The present paper describes the grain size refinements of Mg alloys (AZ61, AZ91, ZK60) by HDDR treatment. As a result of the HDDR treatment at 350°C under a hydrogen pressure of 7 MPa for 24 h, following by evacuation at 350°C for 3 h, the grain size of AZ61 alloys was reduced from 10∼20 μm to 100∼200 nm. At the hydrogenation stage for the AZ91 alloys, the disproportionation reaction occurred with forming MgH₂, Mg₂Al₃ and Al phases. At the following desorption stage, the three phases were recombined and the Mg-Al-Zn solid-solution alloy was reformed. After the HDDR treatment, the grain size of AZ91 alloys was reduced to 100∼200 nm. For the ZK60 alloy without Al, the grain size was reduced from 2∼20 μm to about 300 nm by the HDDR treatment.