Grain Refinements of Al–Mg Alloy by Hydrogen Heat-Treatments

Abstract

The present paper describes the grain size refinements of an Al–7.8 mass%Mg alloy by hydrogen heat-treatment of so-called Hydrogenation–Disproportionation–Desorption–Recombination (HDDR) process. Upon hydrogenation of the alloys, a disproportionation reaction occurred in forming of MgH₂ embedded in Al matrix phases. In the subsequent hydrogen-desorption of the alloys, MgH₂ was decomposed and was resolved into Al matrix phase, in resulting in the original solid solution of the alloys. This means that the HDDR phenomena take place in the Al–7.8 mass%Mg alloy. It is rather surprising that the grain size of the alloy turned into a several 10 nm after HDDR treatments such as heat-treatment at 350°C under hydrogen pressure of 7.5 MPa for 72 h, in following by the hydrogen desorption treatment at 350°C for 4 h in vacuum. This could be the first report that HDDR treatments are effective in producing the fine grain size of the order of nm in Al-based alloys.