Preparation Of Ultrafine Grain Magnesium Alloy By Accumulation Roll Bonding And Microstructure Refinement Mechanism

In this paper, the hot compression behavior of AZ91 and AZ31 magnesiumalloy at the temperature of 200-500 ℃ and the strain rate of 0.001-10 s^-1 wereinvestigated. It was shown that as the strain continuously increased, hotdeformation of AZ91 and AZ31 alloy resulted in dynamic recrystallization.Nevertheless, since the peak flow stress and the cracking susceptibility increasedwith the strain rate and reduction in deformation temperature, the feasibleprocess regime was restricted to a narrow range, for example, at the temperatureof 350 ℃ and the strain rate of 0.01 s^-1 as an optimum operation for a perfectmicrostruce of AZ91 and AZ31 alloy. Their activation energy for hotdeformation is 80.1 kJ·mol^-1 and 60.8 kJ·mol^-1, repectively. The microstructureevoluation and grain refinement mechanism of AZ91 and AZ31 alloy imposedby hot compression and accumulative roll bonding was also examined usingGleeble isothermal compression test and actual rolling operation in lab scale. Itwas discovered that during the multiple accumulative roll bonding of AZ91 andAZ31 alloy performed at 350 ℃ and 0.01 s^-1, the microstructure was mainlyrefined in the earliest operation and increasingly uniformed under the remnantdeformations. The mechanism for the grain refinement is accumulation ofdynamic recrystallization caused by each deformation. Ultimately, thehomogeneously grained AZ31 magnesium alloy plate with 2 mm in thicknessand 3 μm of grain size in average was successfully produced by three-runaccumulative roll bonding of a cast.